Questioning the reliability of the 996 (starting problems) + Fuel Vent System(PICS)

So, I've owned the car for a couple months now and it has broken down not once but twice at the gas station. First time I had it flat bedded home. After some troubleshooting, i replaced the fuel pump, relay and fuel filter. She started right up. Recently I've cleaned the MAF, Throttle body, reset the ECU, changed the oil, replaced the spark plugs, cleaned air filter, replaced fuel pump, replaced my IMS bearing, flushed tranny fluid, replaced carbon control valve. Now, today the car started like any other day. I drove home for lunch and as i started it to leave it sort of struggled to reach operating idle. I thought nothing of it at the time. The the issue did stick in my mind prior to me reaching the gas station. After getting to the gas station, I filled the car up from just below a 1/4 tank. Went to start... Just cranking.... and cranking. No firing. Fail. Out of every car I've owned, I never had two breakdowns. No matter what the mileage on the engine or age of the car. I'm looking for some input on this particular problem. My thoughts are the ignition system since i just did decent maintenace to the fuel system. ALL input welcome. I need to be prepared so i can tackle this issue after work today in the gas station parking lot.

argh man that sucks... ! Did you manage to start it up at some point or you had to tow it again ? I feel your pain as I am struggling to debug my cold start problem. yesterday problem again, this morning, no problem... I bet tomorrow it will be there again.. I have this durametric tool that contains tons of values, unfortunately without a good manual I can't do much with it. Is there a place where the durametric values are explained ? or something to help troubleshouting with the durametric ?

I dont have a ECU reader like you. I'm going to attempt to revive this paper weight In a couple hours.

The durametric values should be available online. r1de23, sorry to hear about your troubles. My 996 has been very reliable. I do have the occasional start where the engine cranks a little longer, but not often. Good luck with the fix!

BTW: the fuses are good.

Sorry man Do be surprised to find its something that you have already replaced (fuel pump) but like your initial thought, it better be something else That said, IIRC ignition failure (ie electrical) throws a CEL Good luck, these cars can be great....

Anyone have an details on the ignition switch under the dash? Possible culprit?

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They are great when you can drive them.

Did you conclusively diagnose the first problem to be the fuel pump?

Same gas station?

Fuel filter? They should be replaced every 60K miles. You have a 99-01 right?

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+1 There are some photos on here at the end of one of the threads regarding ignition s/w When the ignition antenna ring on my 5 series BMW failed it caused all sorts of weird and wonderful problems.

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Different gas station.

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Replaced it already, the last time it broke down.

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I was actually shooting in the dark at the time (i knew little to nothing about the Porsche) I bench tested the fuel pump and it would not pump while submerged in fuel. So I "assume" it was the pump. The relay and fuel filter were replaced as well. My carbon control valve was howling after the fact, so i repalced that a few weeks after i "fixed" the first break down. Throw out some more ideas for me, so i can hopefully get this thing started at the gas station.

I don't think you fixed the problem the first time. I think an issue surfaced, you replaced a bunch of stuff using the method that if you start replacing things, eventually the faulty item will be addressed and the car will be fixed. This method seldom works on something as complex as a Porsche or any modern car full of electronics. You need diagnostic equipment and a service flow chart to check the various systems that contribute to whether a car will start and continue to run. I do this stuff for a living. Good Luck

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I've read many threads on the switch and it seems to cause the car to act funny in various ways when it starts to go bad.

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I 100% agree that i need the diagnostic equipment. Do you have this "service flow chart" that you speak of?

ride 23, read the recent ignition switch post. not sure if thats your problem but if your key doesnt turn easily or is stuck in the ignition this is an easy DIY fix. 9$ part yada yad yada

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I wish I did, I've love to help. Maybe someone here has a service manual and can help. I think the Boxsters and 996s are very reliable overall. We've had a boxster about 8 years and a 996 nearly 7 and only one time did the Boxster not start when the battey was on it's last legs and she called me for a jump. Other than that the reliability has been great.

Hope you can sort out your no start issue. If your Porsche is throwing a CEL, then by all means share your fault codes to enable a fix. I understand your frustration and hope it can be shortly remedied.

Yeah, no CEL light at all. I'm going to use an OBD2 reader from a friend to see if it will show anything. I doubt it, those OBD2's are so generic. I'll post an update after i figure it out.

What surprises me that you have no codes thrown. You've fixed a lot of the things I would have suspected..fuel pump being #1. Usually MAF would throw a code (i believe), but a bad MAF would give you those results. Maybe a quick clean? Maybe the connector is loose? Ignition module? Doesn't the 996 have 6 ignition modules..one on each plug? If so, I would suspect if 1 went bad, you would start, but get rough idle. So that doesn't sound likely. Does it even sound like it's trying to catch, or it's just a constant crank? If it's catches a bit...then I'd check your air intake tract (post MAF) to see if there is a vacuum leak somewhere. I had a Supra where the intercooler cracked...drove me nuts to find the problem. Fuel injectors? Possible, but again, I would be surprised if all of them died. One of then would give you a really horrible idle, and would definitely trigger a code. Fuel pump again? Maybe...did you ever stare at the voltage meter when started? Is it below 14.4V? I remote chance, but if you're spiking a lot (aka bad alternator), you could potentially fry the fuel pump (amongst other things). One more thing....how below 1/4 was it? Was the fuel pump completely submerged? I have read that low fuel too often can cause fuel pump failure (aka being submerged in fuel cools the pump), but I have never personally experienced it yet. Dunno man...this is all I can think of off the top of my head .

UPDATE: The car started after sitting for 4 hours. I had a feeling that would happen. The engine ran perfectly fine after. I have an idea now. Somehow, when my fuel tank gets low (below a 1/4) and i fill the tank it dies. That is why i've been dying at gas stations. I need to figure out the systems that could prevent the the fuel from reaching the engine. Maybe the cold gas introduced into a hot tank somehow creates some sort of vapor lock or something related. I have no clue. any ideas?

Just ran OBD2 codes: P0650 - MIL Control Circuit Malfunction P0410 - Secondary Air Injection system Malfunction P1411 - Manufacturer Controller Aux. Emission Controls Any thoughts?

I dont know how long those codes have been in the system, i cleared them and i will re-flash the ECU tomorrow. The last two codes dont seem related to my starting issue. Im not sure about the P0650. That first code sounds like a malfunction for my CEL indicator, am i wrong?

Wait... is your cel bulb on when you turn the key in the acc position..... you mention you dont see a cel light, but yet have error codes that the cel light should be on. Your bulb blown? That may explain the PO650 code.... Is the 2ndary Pump turning on?

Sorry to hear about your troubles but since nobody has asked, I will..... Did you get a thorough PPI on this car that you have only have a couple months??? Have you taken to an indy or the dealer to have the problem identified or are you just throwing money and parts at it hoping it will fix itself??? You could save yourself a lot of grief, frustration, and $$$.

I suggest you also try Renntech.org as well to broaden your audience. Loren provides excellent help there. If your CEL bulb was burnt or not functioning, that may be good news since all those codes (if they come back) will help you zoom in the culprits.

haha, well that explains why my CEL light was not on, the bulb was blown. Fixed. It actually never occurred to me that the CEL never came on when i turned the ignition on.

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There are only 3 variables, air, fuel, spark. If you've tried all 3 with no results, and aren't too attached, you may have a problem car, and you may want to cut your losses. Usually these cars will tell you what's wrong at the OBD port if it's a sensor or a plug or a coil issue. For what it's worth, I drive my 996 more than both of my other cars (MB+BMW), and it has been one of the most reliable cars I've ever owned with the sole exception of the coil packs. I'm on my 3rd set (all warrantied) Edit: I just saw your result (restart), there have been a few posts here about an issue with the venturis in the fuel tank causing a similar issue to the one you described, however it could very well be the level sender

i've been looking for 993's and 996's trying to evaluate the reliability and so forth. ...i've got hopes to make a purchase next year. Anyway, yeah. I don't own either, but i thought i'd write that I had very very similar symptoms with my Audi A6. It would die at 1/2 a tank. ...Then I changed the fuel pump and the car worked perfectly except it would die at a 1/4 tank. After about a year, a new problem had developed and the car wouldn't start after it was warmed up. It would crank and crank, unless I let it cool down an hour or so. This was very frustrating, since none of these issues caused CELs from what I remember. It was also annoying that I paid 3 local Audi mechanics to fix and they could either not diagnose or wanted to charge me a lot. Ultimately, I gave the car to my brother in St. Louis (I'm in Phoenix), and dropped it off at his very trustworthy mechanic. He diagnosed the 1/2 and 1/4 tank issue to a faulty fuel sender. The starting issue was the camshaft position sensor. He also warned me that with Audi's, mechanics often don't fit the fuel pump tight and that'll cause similar symptoms. I hope these suggestions can apply to your troubleshooting... Good luck. BTW, the A6 now runs perfectly with those two fixes, btw. It's been reliable for several months now.

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How does this comment help fix the problem anyway? First off, I will never bring my car to a dealer for anything (saves $$$). And, its not like I don't have a clue how a car works and im not just "throwing" parts at it. Initially I said I was shooting in the dark to begin with since I was not familiar with the Porsche during my first break down. Now, frustration on the other hand will never be eliminated because all mechanics get frustrated no matter what the job is. Its very easy to just hand a problem over to the Porsche dealer and it is miraculously fixed when you pick it up. But, I not going to lie that i was not terribly frustrated today at the gas pump.

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Fuel level sender? Elaborate....

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Thats funny your using an Audi as an example. I just told my wife today that i missed my damn Audi S4 because that thing always started every time.

anyone have a wiring diagram of the fuel level sender?

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I don't have the diagram, but I recommend visiting renntech and searching the 996 sections. I do have a page from the 996 workshop manual you may find interesting in the event that you did not perform the calibration procedure.

i disconnected the battery prior to replacing the level sensor, it says the it does not require recalibration. My gauge is not off, it is full when it is full, etc..

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Sounds like you are missing the point of my question and totally skirted the answer. You really think you are saving money??? Have fun.

intolerance of ignorance. How are you supposed to get help when you don't seem to get it? The help is here but shooting in the dark is a waste. So, I'll ask again. Why did you not answer my questions?

How about you explain why you think i am shooting in the dark regarding this issue?

Three things needed to run, compression, spark, fuel. We know you have compression, you need to check for spark and fuel when it won't start. Crank the motor half a dozen times for 5 seconds, rest for 10, etc. Now sniff the tail pipes, smell gas? If so, you are getting fuel, if not dig deeper and find a way to verify fuel is entering the combustion chambers. If you are getting fuel, verify that you are getting spark. This could be difficult to do in a conventional manner. Pull a coil and place a spare plug on the high tension lead, ground the threaded portion and have someone crank the motor. Look for a spark. I'm thinking this will get you going in the right direction. Good luck

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Because you didn't answer my first questions. A full PPI and taking it to an Indy would have either identified the problem or excluded the problem. Personally, if I just bought a car and a couple months later I was having problems I would talk to the selling dealer or the place that did the PPI and see how it was missed. You seem to have a disdain for shops. Why? As far as shooting in the dark and questioning the reliability on these cars you did........ replaced the fuel pump, relay and fuel filter, cleaned the MAF, Throttle body, reset the ECU, changed the oil, replaced the spark plugs, cleaned air filter, replaced fuel pump, replaced my IMS bearing, flushed tranny fluid, replaced carbon control valve. You tell me, but from what I can tell, that is throwing everything at a problem and hoping something sticks. Are the shops in your area that incompetent that they could have no looked at your call and diagnosed this problem?

I use to have the exact same problem a couple a years ago with my 964 1991. I was in Florida for a 2 weeks vacation so without any sign one day the engine crank and crank again with no success..... I waited for half and hour and the engine start with no problem... Same thing happened 3 or 4 days later I brought the car to the Porsche dealer and they replaced the gas pump relay...$100.00 That was a recurent problem with Porsche car at that time. Your problem is most probably the same Good luck Robert

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Bingo. That's the point I was after with the OP. We'd all love to see him get his issue resolved but it starts with taking the correct approach.

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BTW: The only thing i did that i thought would fix the problem without knowing for sure was the fuel pump. Everything else on that list is what i do regardless for tune-up purposes..

sure, we'll go with that. I really hope you find the source of the problem.

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What is the purpose of this forum? Is it a place where you all can sit here and talk about your dealership experiences? I thought it would be a group of DIYers and owners that want to learn about cars that help each other to fix problems..... apparently i was wrong.

Last post from me since you still don't get my asking........ You aren't wrong, you are exactly right what this forum is. But by asking you the questions I did we can get a better understanding of what is going on with your car. I never said it was about our dealer experience. You are still missing the point of my questions. Have a meeting to get into so I have to run. I sure hope it isn't pride getting in the way or your disdain for asking the help of indy or dealer that is going to keep you from fixing this.

Ride23....I wouldn't be that harsh....I have gotten so much DIY info off RL that it has saved me a wheel burrow of cash. These are fairly sophisticated cars to diagnose issues at times. The only way to it is to have the proper equipment in order to get zero'd in. I don't have the durametric, only a OBDII, but I can go to indy or a P-car dealer to get things diagnosed. Than I decide if I want to tackle it or not. What others are trying to say (I think) is just that. This route will cost $$ just for them to look at it but you save big when you know what the issue is and than DIY instead trying to assume things by thinking it is this or not and start replacing things that were good. Also I seem to remember the 996 had a recall regarding the gas tank sometime ago. Might want to check into that too. Hope this helps. If not.....good luck

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You weren't wrong. There are a lot of DIYers on the forum, and you will find a lot of help. We also will discuss dealership experiences if we have them, good or bad. Dell is a good guy, and very knowledgeable. He just asked some questions, in order to help you better. You didn't answer. Did you get a PPI? If so, you can go back to that guy and he should help you diagnose the problem properly. If not, then just say you didn't and we can go from there. You sound like a hands on guy. You need a durametric to diagnose problems, a dealer or indy will have them until you get your own. Without a proper diagnosis, you are shooting in the dark. It I were shooting in the dark, I would start by replacing the least expensive suspect (ignition switch) and work my way up. You can get the part at a VW or Audi dealer for less than at a Porsche dealer. Part # 4A0 905 849B. There is a recent thread with DIY instructions. Good luck with the repair.

+1 on durametric... its a Porsche specific tool that you need if you are a DIY type person. It will also help you learn about your car since you are new to it..... The other codes you have sounds like a failing cat..... I had the same code for about 6 months and eventually turned into cat specific cels.... then I replaced my cats and all was good again. The gas pump relay sounds like a good lead..... let us know how you make out.

David summed it up nicely for me. Thanks David Listen, if you don't want to answer the questions then that's your call. I was merely trying to understand what the situation is. By not answering and you obvious disappointment with the car right now my take was somebody that was thick headed when it came to the need to have a thorough PPI and to proud to ask an indy or dealer for help. Sure, we're here to help. But when you start throwing darts a a board through trial and error it just doesn't make sense when you say you are saving money. Anyway, let's start over........ There are plenty of guys here that WANT to help you out. Me for one will do whatever I can to help out as I was helped out tremendously in my early days of ownership. With that said, I have never been too proud to let somebody else fix a problem for me. I have a vast amount of knowledge working on these cars but also know when I am spinning my wheels. So, as we understand more about your car, the history, and what you are able to diagnose, we can go from there. Right now, everybody is just guessing since it seems you are holding something close to the chest. Understand, this is nothing more than one big support group. Introduce yourself, admit your an addict to the brand, be honest, and ask for help if you can't do it.

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I'd guess about 30% are DIY and knowledgeable the rest are well........ I guess you have noticed

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Let's start over for sure... I think we just ran into some misunderstanding with each other for a moment and ended up getting off topic.

Now, Let me post an update along with some history. Honestly, I was trying to avoid the nagging about bringing it to get a PPI prior to buying (which i see all the time on this forum). I did my own thorough inspection. As for the car's history. There is none, records were lost between dealers of course. I only have some word of mouth from dealerships and previous owners. So, I saw a opportunity and took it. As you all know I'm all about getting my hands dirty. The first thing major fix I've done to the car was the IMS retrofit. While steadily tuning up the car, I can right off the bat I can eliminate possible culprits to the problem. (the listing at the beginning of the post) Today, the car started right up. No CEL at all. Runs great. Except i noticed that howling noise that occurred months ago has re-emerged. It is coming from the vent behind the gas door. (see picture) Weeks ago, I followed the vent down to the carbon control valve. I figured the valve had failed and i replaced it. Now, it has come back. I am beginning to think that there is a link between the vent system and fuel system that has lead to my car break-downs at gas stations.

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i replaced the fuel pump relay.

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Recall Date: APR 10, 2000 Model Affected: 2000 PORSCHE 911 Summary: VEHICLE DESCRIPTION: PASSENGER VEHICLES. INCORRECT PROGRAMMING OF THE ELECTRONIC LOGIC UNIT CAN CAUSE AN INCORRECT FUEL LEVEL. Consequence: THE VEHICLE COULD RUN OUT OF FUEL CAUSING A LOSS OF POWER. Remedy: DEALERS WILL UPDATE THE SOFTWARE IN THE INSTRUMENT CLUSTER SO THAT THE FUEL LEVEL AND THE RANGE OF REMAINING FUEL ARE DETERMINED AND DISPLAYED CORRECTLY. Potential Units Affected: 2734 Notes: PORSCHE CARS N.A. INC. Read more: http://www.motortrend.com/cars/2000/...#ixzz0rmvsQjuA Read more: http://www.motortrend.com/cars/2000/...#ixzz0rmue8HS3 Look what i found, good call.

The only thing is i never ran out of fuel.

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Well said. To the OP, please continue to ask questions. Many of us here have real mechanical knowledge and support this forum as a way of educating ourselves about these wonderful cars. I, too, do not subscribe to the simply "drop the car off at the mechanic and let them figure it out" school. On to your problem. I think you're on the right track. An important clue is that your problems occurred at the gas station while filling the tank. Therefore, it might make sense to familiarize yourself with the vapor recovery system. May I suggest purchasing a full set of service manuals (you may be able to find a set for free download on the internet). These are really necessary if you what to maintain the car yourself and will provide you information on how to troubleshoot and test various systems in the car. On the bright side, these "little" issues provide a chance to get in there in learn about your Porsche. Good luck! Joe

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Well almost right?.....looks like a lot of us are scratching our heads with you!

I should have elaborated on the sender thing. I don't mean to give elementary advice to a seasoned mechanic, so pardon me if you find this post too simplistic, just take it for what it is or isn't worth: I noticed you replaced the fuel pump. When you reinstalled the sending unit, did you notice a marking on it? You would have to turn that marking to match a similar marking on the tank itself. I also thought that it was possible that in fact your original error was a faulty or miscalibrated sending unit which was informing the computer that the car was empty when in fact it was not. Since calibration is fairly simple if you have someone nearby who will hook up a pst, i thought it was worth giving you the procedure. Even fairly seasoned DIYers rarely get too deep into the fuel tanks on these cars, but I'll share some thoughts: 0. Invest in the durametric software, as a DIY guy you will find it invaluable in working on these cars 1. You replaced the fuel pump, but did you measure flow with the new pump and the tank down to 1/4? If it's not giving you enough pressure, it could be the tubes or venturis in the tank itself. It could be the fuel lines (including the return line if Mk1, bosch systems rely on return as well). It could be the filter. Nominal test values: Stationary engine 3.8 � 0.2 bar Engine idling 3.3 � 0.2 bar 2. If your fuel gauge/trip computer is reporting incorrectly empty or lower than actual, might be worth replacing and recalibrating the sending unit just to eliminate. Cheap. http://cgi.ebay.com/ebaymotors/ws/eB...1#ht_500wt_751 3. Just to eliminate possibilities in ignition, you should bridge the clutch interlock switch (and inspect that fuse) and the ignition switch should also be inspected and replaced if necessary. I really, highly recommend visiting the 996 section at renntech.org, downloading some manuals at http://www.cannell.co.uk/Manuals.htm , and searching renntech's forums. It is a much more technical forum, and you're more likely to see a similar issue there. Finally with regard to your intuition about a connection to the vent system, take a look at it, I've seen stranger things. The fuel filler neck and gas cap also should be inspected. Look at all the fuses and switches that prevent ignition. I have an MB that wouldn't start at a gas station last month. It was a faulty brake light switch, $8, just coincidental. You never know.

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I remember a recent post on one of the forums where replacing the breather cap for the gas tank solved similar problem. Couldn't find post but I remember it. (if this didn't happen 2x at gas fillup, I'd say ignition switch.)

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1. I think i will invest in a fuel pressure gauge to check the pressure. 2. I did notice the marker on the fuel level sender, I lined it up during install. The fuel filter has been replaced, the relay as well. 3. Also, I have jumped the clutch interlock switch already. That online manual is only partial, not even close to being complete. BTW: It is not a good time opening the fuel tank. Do you have a diagram of the fuel vent system?

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I called the dealer and asked them about the recall. Apparently it does not apply to my car so I'm good to go.

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Now that is good to hear. Just throwing a shot in the dark (imagine that ) but could this be a fuel pump issue? If there is any debris clogged it could mimic the same symptom. I had that issue in my RS America. Change the fuel pump and voila!

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"A shot in the dark", what does that mean? When i replaced the fuel pump a month or so ago there was not much sediment in the bottom of the tank and the small filter element on the old pump was barely covered. I doubt the new pump is clogged. Have any experience with the vent system for the fuel tank? I just thought of something else that may help solve the issue. My last time at the fuel pump when it broke down. I filled it up until the pump nozzle clicked and stopped flow, (like usual) i tried to top it off and the fuel squirted out at me a little bit. That usually never happens. Any ideas?

Good call on the pump since you check the filter element and any debris in the tank. If it isn't burned out you can reverse the pump to clear out any debris but since it is new and the tank is clean we can almost certainly rule that out. It does sound more and more like a venting issue, doesn't it? I have absolutely zero experience with that. However, the collective here has got to have somebody that has been in the vent system. Guys???

Hope this helps. link to RennTech 1 - EVAP canister purge valve 2 - EVAP canister 3 - Purge air 4 - Tank 5 - Pressure sensor 6 - Shutoff valve 7 - Operating purge valve 8 - To intake manifold 9 -Vacuum control valve

i need a shop manual so i can get tolerances/voltages/etc for specific sensors and valves...

Also, the breather port located behind my fuel door sucks in some serious air. any idea where that air goes? back to the evap canister? or fuel tank.

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How do you go to revert the fuel pump ? I mean I wonder how that work..where does the gas go ? I am struggling with a fuel thing myself and I suspect the computer would shut down the fuel pump in case there is too much 'negative pressure'/suction, in order to prevent any damage to the fuel pump. So the question is what is releasing the pressure in the tank, is that the "1 - EVAP canister purge valve" ? If yes I wonder where is is located ?

It just goes back into the tank

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the #1 is probably a check valve that goes to the intake manifold..

Doesn't 996's have a problem with the fuel venting properly? I remember reading threads on the pump stopping before the tank is full...

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You should be able to find the factory manuals on Ebay. The CD versions sell for around $15. If you want a paper copy, just print the PDF on the CD.

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I'll look into it. thanks.

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Mine fills properly, the gauge read full as well

sent you a pm

Another update after driving today... the car started and drove fine but as soon as i would let my foot off the gas pedal the howling noise would start and as soon as i stepped back on it the howling went away. I saw there is a positive intake manifold draw tapped from the EVAP canister, any ideas why it would make this noise behind the gas cap though? Where are my fuel vent specialists?

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anyone have any ideas where #1 is located at?

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This might help. Got it from a old thread on RL. http://www.pelicanparts.com/cgi-bin/...1999-05)%20%20 I did a google search and the RL post showed up. Hope this helps.

that looks like it goes into the right side of the throttle body? am i seeing that correctly? how do you know #30 is #1 in that other diagram?

I did a search for "EVAP canister purge valve". That is what came up. I'm not a mechanic by no means and it does appear to be at the throttle body per the diagram. I suggest doing a search here on RL with those key words. Not to be short Ryan.....but if I can find this stuff so can you.... Good luck!

Trust me I usually try a search prior to me posting. I cant find anything on the EVAP canister.. I posted in Renntech, maybe they have some ideas. I've seen other guys with the same problem as me though. I'll post updates.

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Good move. It's less active but the contributors are more technical

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does anyone know the functional purpose of the purge valve (#7)?

Here is another diagram ive been looking at......

Lets try this one..

Don't know but looks like I was off base......my apologies

More diagrams....

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I wonder if this valve you are talking about connects to #3 in this diagram?

You could be onto something, it is definately something with a issue of vacuum / pressure. Its as if your fuel system is starving itself when it reaches a certain point.

im think maybe the fuel tank becomes over pressurized which somehow starves the injectors...

Sounds like you are progressing.. The vacuum system is really a pain to understand ! My car is a C2, so to get access to the gas tank I need to remove the battery and all, but if you can, I'd suggest may be to remove completely the tube that is on top of the fuel pump, the one which is not the fuel line output of course. I assume that tube is only there to let the air in the tank ? At least this would make you pinpoint the problem for sure. Next time my car has a start problem I think I'll try that.

i need to figure out what the purpose of the bleeder valve behind the gas cap does.. there are numerous shutoff valves and control valves..

this makes no sense, seems like most people when they have an evap problem the CEL comes on. maybe its my gas cap?

Alright, I finally dove into the fuel vent system. the diagrams that i was given do not come close to what is on my car... MANY pictures to come...

Can't wait to see your finding, the fuel system is really obscure ! I wanted to let you know that my idle problem did not appear since I filled my tank with a Techron bottle. I don't want to Jinx it, but so far, I am good...

Here we go...

Sorry the pictures are out of order, this is another picture of the hose that leads from the valve housing that i disappears into the car. Where do you think it does? Here is the fuel line vent valve. The housing where the carbon control valve and shut-off valve are located. Drain line where the fuel overfill drains under the car.

What do you think that blue valve is? I blew into it and it doesnt do anything, my first thought was that is was a check valve of some wort. Carbon canister Three ports purge, air and tank Valve housing with valves removed Carbon Canister

I pulled the airbox and TB off to check and see if the orifice for Regeneration valve that sucks air from the carbon canister was clear. It was.... I hooked up the valve to 12v and the valve opened as advertised. Here is the purge line that runs to the carbon canister at the "purge" fitting.

I used my air compressor to clear the lines and figure out where they go.. Worked like a charm. I ran the part # for this funny valve looking thing and nothing came up. Here is the vent line valve, i wasnt sure how to check it, so i blew into both sides and the same amount of flow came through. I dont really get the purpose of this thing. If anyone has an idea let me know.

This is a picture under the battery tray. This line leads to the fuel line vent valve. Carbon control valve and shut-off valve. I also hooked up 12v to each and they worked as advertised.

That little fitting on the left side of the valve housing is the UNKNOWN air source im talking about I tried to label them so i wouldnt forget. This is the hose that i cant figure out where is comes from.

After clearing all tubes, inspecting all lines and testing all valves. here are my conclusions on the vent system. there is one line that i cannot figure out where it goes and i think it is the culprit with my howling noise from behind the gas door..

The unknown source labeled is the line that i can figure out where it goes..

Now, here are some notes that i wrote down as i was testing the system with the engine operating... If i open the gas cap and push in the flapper (as if i were to refuel the car) the engine starts to bog down and die. ( i did this to figure out when the carbon valve operates) The carbon valve is ALWAYS closed during operation of the engine The shut-off valve is ALWAYS open until i pull the valve out of the housing while the engine is operating and then it tries to close.

Conclusion, The howling noise from the vent behind the gas door leads to the carbon control valve. I think that the unknown air course that leads to the housing where the carbon valve and shutoff valve does not supply enough air through the tubing that leads back to the carbon canister. I believe that the engine is trying to suck enough air through the carbon canister and additional air ends up squeaking by the carbon control valve which ends up recirculating back to the intake manifold through the regeneration valve in the engine bay.

Note: When the engine was operating the regeneration valve was clicking on and off intermittently. Is this normal? As soon as i disconnected the harness from the valve the clicking stopped. I wonder why it would open and close like that.

nice job on the pics, some caption would be great I feel I understand what they are, but I'd be interested to read your comment.

ill add a caption in a little bit...

Another quick thought.... could someone remove the plug from their own regeneration valve while the engine is running and give me the voltage running to the valve? mine is ~ 10 volts. I want to make sure thats within spec.

Great pics. Looks like you are zeroing in on a conclusion!

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any idea where that unknown air source comes from?

BTW: This howling noise coming from behind the fuel door is very annoying. Feels like im driving around a glass coke bottle w/ the wind blowing over the top...

i think i scared everybody off with this "technical" stuff. lol.

I don't think anyone has done this work so far. Where is that valve you are talking about , the one where you want a voltage check ? phil

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We are better at cup holders..

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[Image-only post; no author-written text. Original image references:] https://rennlist.com/forums/graemlins/roflmao.gif

so those pics did scare everybody off any update on your vacuum problem ?

not yet. i havent had the opportunity to dig into anymore.. im seriously lost at this point... i wish there was some more experience between rennlist and renntech on the fuel vent system. i've read through tons on renntech and im still stumped.

This is the first time Im hearing about this howling problem? could it be an overpressure issue?

Im not sure, the air vent behind the gas door sucks in air and makes a howling noise while i drive. Maybe it has something to do with my car randomly not starting. The howling only seems to occur when the vacuum from intake/throttle body decreases.. but disappears when i step on the gas pedal. its very odd. it pulls are past the carbon control valve which is about 2 feet below the air vent behind the gas cap... the valve is operating fine... does anyone know when the carbon control valve operates? i know the valve opens when i actuate the switch in the filler neck.

Wow long thread. No time to read all posts but...... You say you cleaned the MAF but did you touch it with other than the spray? MAFs don't like being touched even if its a q-tip soaked with cleaning solution. I used a can of air to help get extra MAF cleaner fluid out on mine in case any of the weird recesses got debri washed into them or gunk wasn't displaced. Darn near used a full can so I imagine it got pretty clean.

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about 1/3 of the thread is off topic.. i never touched the MAF after cleaning it..

oh BTW: I've been filling my car in the garage off of gas cans so i can avoid the embarrassment of breaking down at the gas station AGAIN.. the car started right up after putting 5 gallons in, very odd...

UPDATE: Due to the fact that I've had less time lately, I've barely had the chance to trouble shoot the issue. Today, the idle was acting funny (like usual) and i remembered that people had unplugged the MAF to see if the idle would stabilize. So, I did and the motor completely went dead as if someone turned off the ignition key. This doesn't seem normal, any ideas?

humm you might want to try a new maf, me I once forgot to plug this thing back in went starting and the engine would start exactly as normal..In fact I only came to realize I had forgot to plug it back as the CEL light came up ! BUT I never heard of anybody trying to unplug it while the car was still running. confirm you unplugged it THEN try to restart it ? or if you unplugged it as it was already running. in the second case I would not be surprise the computer would be 'unhappy' and **** it all down.

What is the part number on the valve coming off the throttle body? It looks like a valve that I had fail on the audi. There should be a small screen in it. See if that screen has debris in it.

My car runs fine and I've unplugged the Maf Sensor while the car running. The car shut down straight away.

I waited until i drove the car and after i returned home i tried unplugging it again. The car almost died but recovered and idle the same as it did before. I think im going to rule out the MAF.

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The only # on it is 0 290 142 323. But it looks exactly like http://www.pelicanparts.com/cgi-bin/...0%281999-05%29

Well?? After 9 pages what is the latest?

This isn't good during the heat of summer with all those hot women needing you out there to day dream about and make cats calls to.....uh I really said that didn't I? Anyway good luck getting on the road.

haha, I dont have much of an update. As of right now i am scared to go to gas stations. I've been using red gas cans in my garage for now with no issues so far.

I ran a bottle of fuel system cleaner through my car as well. No changes.

Might be time to contact one of these places.... http://www.pcarshops.com/porscheshops/nebraska/ Let us know what it is when you find it...Good Luck!

MAF sensors do strange things. I agree with Phil that you should buy a new one and plug it in. You should be able to drive without the MAF. It will idle and run terribly under 3-4000 (which is why I would replace yours) but act normally at WOT. I've run an entire race weekend with a unhooked MAF without any consequences.....

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I'll pretend i didnt see that.

Does anything think my EVOMS v-flow CAI has anything to do with it? or my ECU upgrade?

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I guess you are perfectly fine with filling your car in the darkness of your garage with 5 gallon gas cans because you are embarrassed to fill it in public..not sayin' just sayin'

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it is quite peaceful filling the car in the garage...

I would check the tank vent valve operation, it is a two wire valve on the intake manifold that has a vent line to the neck area. If it is sticking at times it could possibly flood the car from the vent fumes while filling the car thus not allowing it to start, possibly an intermittent problem. It will cause the noise you are explaining as well. It's possible when you fill the tank with the 5 gallon cans in the garage they don't pressurize like at the gas pumps enough to cause the problem. Make sense ? Sound like your problem ? Other thoughts and things to check ..... The MAF as JR stated can cause weird problems, depending on miles on the car it might just be not so bad to just replace it so it doesn't cause any problems in the near future. Another would be to double check things from work recently done. - You mentioned doing an IMS I believe, how is the positon sensor ? Any chance it got moved or a wire pinched somewhere ? Just a few thoughts, take them for what they cost you, and let us know what solves the issue.

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are you talking about this vent valve?

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Yep

Can anyone by chance get the voltages leading to the valve while the engine is running? I'd like to compare..

Like I posted before there should be a small screen on the inlet side of that evap valve...it could be clogged. Remove the screen (most audi techs do) and try it out. I think that valve is the culprite, its common for those to go bad in audis. It would give intermittent starts with my big turbo B5. Replace that valve first....then if all else fails replace the MAF. http://www.ecstuning.com/Audi-B5_A4-...ission/ES6114/

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the unit is sealed shut....

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Replace that valve. Almost 100% thats the culprit. When you get the new valve cut the old one open...youll see the screen Im talking about.

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Will do, i will post an update after i order it in a couple weeks. Thanks.

Now I'm not one to say 'I told you so' but........

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Cool....that valve if clogged or partially clogged will give an insufficient pressure reading and wont open/close properly when it supposed to. If that doesnt work, try the MAF. I understand people are strapped for "play" money, so lets start with the cheapest part first and work our way to the MAF.

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yea i know. my play $$ funds are low.. plus i priced a MAF and it seemed to range $200-250 range.. ughh

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we cant say anything yet. the problem is still unsolved..

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I know but I got giddy...... The world awaits!

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i'd like for someone to give me the voltages they read to that valve while the engine is running so i can compare.

Some basics of the system .... 2000 Porsche 911 Carrera Cabriolet (996) F6-3.4L Vehicle Level Powertrain Management Emission Control Systems Evaporative Emissions System Testing and Inspection Evaporative System Monitoring Evaporative System Monitoring Evaporative System Monitoring General Description The fuel evaporative system monitoring permits detection of leaks with a diameter of 1-mm or larger in the fuel evaporative emission control system. Additionally, the monitoring system can detect a malfunction of the fuel tank pressure sensor (DST), canister close valve (AAV), or purge control valve (TEV). The system monitoring is performed by observing the fuel tank. A canister close valve (AAV) and a purge control valve (TEV) are used to open and close the system. Monitoring Conditions The leak test will be conducted when the vehicle is at an idle condition with zero vehicle speed. Plausibility Check DST The TEV is closed by a continuous reduction of its duty cycle. Afterwards the pressure is observed. If the pressure falls short of a threshold (vacuum) for a given period, an AAV malfunction is detected (AAV blocked) and monitoring is stopped. If the pressure is not steady, a DST malfunction is detected and monitoring is stopped. Measuring of Compensation Gradient If the pressure is steady and the AAV closed, the pressure increase caused by fuel evaporation is measured and stored after a certain period. If the pressure reaches a specific threshold, monitoring is stopped, because the fuel evaporation is excessive. If the pressure reaches a specific threshold (vacuum), a TEV malfunction is detected (TEV stuck open) and monitoring is stopped. AAV-Check The AAV is opened and TEV are opened by a constant increase in their duty cycle. If the pressure reaches a specific threshold (vacuum), an AAV malfunction is detected (AAV blocked) and monitoring is stopped. If the pressure does not reach this specific threshold and the TEV has reached a certain duty cycle, the AAV is closed after a time delay. Large Leak Detection If a large lean correction of the lambda controller is detected, monitoring is stopped. If monitoring were to be continued, idle instability will occur because of the high canister load. If the negative pressure build-up gradient is below a certain threshold, a large leak is detected and the diagnosis is complete. If the pressure reaches a certain threshold (ex. -8 hPa), the TEV is closed. If the pressure reaches a specific threshold (ex. -15hPa), a TEV malfunction is detected (TEV stuck open) and monitoring is stopped. Small Leak Detection -1.0mm The system is now considered sealed. The gradient of the negative pressure decay is converted into a volume flow (air streaming in through a leak). Afterwards a volume flow balance is realized. The leak volume flow is derived from the volume flow balance. If the leak volume flow reaches a certain threshold, a small leak is detected and the diagnosis is complete. Very Small Leak Detection (0.8mm) When the Small Leak Detection is finished the same procedure is repeated in a following idle period but with a different level of vacuum and a different (more stringent) threshold. A leak of app. 0.8mm can be detected.

Monitoring of Fuel Evaporation System - Fuel Evaporative System

Monitoring of Fuel Evaporative System - Plausibility Check of Fuel Tank Pressure Sensor

Diagnosis of the Fuel Tank Pressure Sensor

Thats not the voltages,sorry but I don't have a 2000 996 in the shop at the moment to measure, but it should be enough for you to confirm if it's bad or not. Although with the noise you are having and the problem, it's a pretty good guess. As said by others it's fairly common to see it go bad, and the usual complaint is of the noise.

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Finally, some technical data to work with... It seems to me that the TEV is also known as the regeneration valve.

Which do you think is the canister close valve (AAV)? The fuel line vent valve or the shut-off valve?

Any results from the testing ?

UPDATE: Hey, old thread.. but I DID figure out the solution to my problem with the fuel system. It was the Rejuvenation Valve located to the left of the throttle body. I can now refuel will no problems and my howling issues are gone.

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After 167 posts! Can I say it now? Post 82.....hint hint. Seriously though, I'm very glad you got it worked out.

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I was waiting for you to chime in! Atleast I don't refuel in my garage anymore!!