Rich at low RPM and lean at high RPM?

Two-Part question : Started getting a check engine light that comes and goes. Durametric has negative values for rkat and greater than one for upper RPMs. Rich at low RPM and lean at upper RPMs? Overall running well. Vacuum leaks are common but negative rkat argues against that. I have been using the car more for daily driving and have experienced rough idle when starting engine if it is warm, for instance if it has been driven 5 minutes or more. Have to pay attention to keep it lit as if it were too rich, borderline flooded with random misfires that clear if I can get the car moving and into the higher RPM ranges. Is there a temperature sensor that doesn't recognize a warm engine and is over fueling to try to start what it thinks is a cold motor? Used oil analysis shows no fuel dilution. 996, 6-speed, 3.4, 2000 New mass air flow sensor New 996.2 fuel injectors Ethanol-Free gas No misfires otherwise.

[Image-only post; no author-written text. Original image references:] https://cimg1.ibsrv.net/gimg/rennlist.com-vbulletin/2000x1802/markup_1000006716_e9ca4163cadd6a9ede85c9c241edac3b59de3e46.jpg

If you are seeing the check engine light, what codes are you reading?

Good question. P1126 and p1133 are the faults. Occasionally I'll get a sensor behind bank 1 fault but I think that's an O2 sensor that compares after cat to before cat to see if the cats are functioning. I don't believe it affects fuel trims. Those are controlled by the O2 sensors ahead of the cats.

So these codes correspond to: Mixture adaptation lower load range Bank1 Mixture adaptation lower load range bank 2 These are commonly seen as errors that occur simultaneously. Looking back there are several threads mentioning mass air flow sensor issues. I have replaced the sensor previously as part of a maintenance strategy because the previous sensor was age unknown. At that time the previous sensor seem to be working well and the new sensor had no significant change. Since then I installed a second new mass airflow sensor in case the first was faulty, again, no change and the car runs well. Therefore I do not think this is mass air flow sensor related.

Have you changed the o-rings when replacing the injectors?

Quotes source post: 19925436

Good question. Made me think for a minute. Yes, new o-rings. Seems like if there was an o-ring problem it would likely not be on all of the injectors anyway so probably wouldn't be the same on both banks. I would think bad o-rings would lead to air leak and lean condition at low load/ RPMs, is that right?

Putting aside the adaptation values for a moment, what are the lambda sensors reporting at low vs high rpm? If the DME can't hold AFR's to target you'll want to drop driving the car for now. I'm no Durametric expert, but it sounds like the injectors are clogged before the spray holes, limiting their flow rate at high flow but not at low flow. New injectors are always suspect to me until tested, I've caught two batches of new injectors that didn't flow up top like they were supposed to, and that led to high-rpm lean running as reported by the lambda sensor.

Where did you buy your injectors? Do you still have their boxes?

Good point. Would clogged injectors run rich explaining p1126 and p1033? Seems like it would be the other way around.

Is 1.3% added in range 2 a lot? There is no range 2 fault code. Definitely don't want to be too lean. Mostly it feels like it's just a little fuel starved over 5500 RPM. I don't keep it mashed.

I can only relate it to when I used to ride Moto. Seems like it needs more juice. I put a new fuel filter in it to exclude blockages and make sure the flow was getting through.

Quotes source post: 19926531

You can never exclude injectors having a blockage unless you test them. Sad state of post-pandemic pandemic car parts in my experience.

How�s your AOS? Checked it with a manometer lately?

If MAF is new, and injectors as well, maybe (a) put two new pre-cat o2 sensors and (b) add a bottle with PEA and go for some spirited runs. It should solve the problem. Clear the codes and report then. The theory behind my proposal is that the o2 sensors say that the mixture is lean or rich. Maybe these require a simple replacement. I wouldnt bet on clogged new injectors.

Quotes source post: 19927164

Yes, I agree. Oxygen sensors are a big part of the equation. I installed new pre-cat O2 sensors, real deal, not generic, from FCP Euro. I'm wondering if it's two problems, Rich at low RPM could be several things. How does the fuel pressure regulator affect low RPM range fuel air mixture adjustments?

Quotes source post: 19927667

If you have new o2 sensors and new injectors and no air leaks, then it is a problem of the injectors. Have you checked for air leaks with a smoke tester? What injectors are you using? Same ones as the ones removed, or a different part number? My rest would be a two steps procedure: 1. Switch precat O2 sensors and see if the problem moves to the other bank. 2. Move the injectors of bank 1 to bank 2 and see if the problem moves.

Additionally looking at the original post please note that - if I recall well - RKAT values make sense during idle. When accelerating you should pay attention to FRAU and FRAO.

Well, just to clear things up, yes, I am most interested in the idle mixtures /trims since those are what give me the error codes. Those are low range /low RPM and it appears I am running rich. The DME is subtracting fuel, which you can see because the Rkat values are negative and that shows that the DME thinks it's rich. in addition d if the car is warm it can be difficult to start it because it bogs. It feels like and sounds like it is borderline flooded. I can keep it lit with aggressive throttle and it will clear . The readings are the same on both sides, both banks, so switching the O2 sensors won't change things. It is not an air leak because that would be the opposite problem. Also, I smoke tested it and didn't see any problems.

Quotes source post: 19928045

Which injectors did you install? Part number?

Don't think it's likely to be the injectors because I changed out the old ones for these Porsche injectors. The previous ones were working and but the 996.2 injectors are an upgrade. They are good injectors and were installed briefly in a track car that ran strong before I installed them in my car.

Pretty consistent fuel trim. I'm getting these with the engine off. Does it make a difference if the motor isn't running? My impression was these are stored values that represent trim over a period of time.

Quotes source post: 19944765

Yes these are the values your car is running. The adaptations. I am wondering about the part number of your injectors because maybe (since these were on a track car) they have a higher flow than the original 996.2 injectors. Anyway, imho, these are on acceptable limits, so no problem.

Yes, the injectors were installed as a maintenance project and upgrade, although it seemed to make the car run stronger they did not make significant changes in fuel trim adaptations.

Why do you keep saying your fuel trims are rich at idle ?? On the values you have posted the RKAT's show around than 1% , which is very good the limit is ~6%....

Quotes source post: 19945032

Because it is minus 1%...

Quotes source post: 19945057

It will never be at 0%.......I wouldn't worry or try to repair anything unless it is over half way to the limit.....ie. over +/- 3% .........It's just doing it's job........

Quotes source post: 19945363

Awesome. Thanks so much. Maybe a tad off and it really helps to know you think it's very reasonable. Man it's running great but I have no reference for these cars. I assumed that, although minor, it might be significant since I'm getting a CEL for lower load range in both banks and I came to the conclusion it was something that would affect both sides more or less equally. How should I address these error codes?

Quotes source post: 19946051

Can you try with PIWIS? Are these errors in your car recent or old?

They have been consistent for some time now. They clear with durametric but slowly drift back. Disconnecting the battery for an overnight with a reset by jumping positive to negative cables for a generous amount of time to drain any capacitors with the battery out and full 60 to 90 second throttle adaptation gets Rkat to zero. Then it starts a little rough for a few run cycles, getting better each time, presumably as adaptation is achieved. The error codes stay off for a few weeks and eventually return. The check engine light will come on, but after a time it resolves randomly so maybe it is only a borderline error fault. It will usually return within a few weeks and seems more likely to happen during light City driving, (sometimes other people and cars just get in the way), less likely to happen during more enthusiastic sessions. Maybe that's my imagination.

Always check the fuel trims BEFORE clearing any fault codes...... I don't know if you are doing this or are clearing fault codes and then running the engine and getting values, but clearing the fault codes will re-set fuel trims to default setting ( not always it depends on the fault code as to what will be reset to default settings) Fuel Trims are "learned values" than can take some time to learn AND if you have an "intermittent event" that causes the fuel trims to go to the limit it will then set the fault code.. Common mistake is to clear the fault code before fully evaluating the values to determine the root cause of the fault code..... I'll hold off on any more Technical procedural info so as not to complicate the issue at hand....but there is a conflict as to the fault code saying the fuel trim limit has been reached but the fuel trim value is fine....

Yes, this is true. Good questions. I do not clear codes before I check trim adaptations and have continued to monitor the values as they change. Anytime there is a significant intervention/modification I will reset to see if there is a change and then monitor over multiple drive cycles. The adaptations can be cleared and reset to RKAT=0 and FRA=1 . After that they then progressively drift to become stable at these values after multiple run cycles over a period of weeks. Eventually it throws a code. The error codes seem to stay fixed once they appear even if the CEL light goes off. If these values are within limits, ( much less than 6), for low range, and I assume they are referring to RKAT values, I'd be interested in what the CEL and error codes are indicating.

OK, So, you are driving around for weeks then the CEL comes on , but you don't test for codes or values right away.....Then by the time you check the fuel trim values they are around 1% right ? A couple of points :: The codes P1126 P1133 can mean either rich or lean......it means the RKAT has reached a limit... You need to pay close attention to the details of the description and additional info from the codes description on the PIWIS ...It will either say "lean limit reached" or "rich limit reached" and it may even say "Above or Below Limit "....This detail is important to know .. Also if you highlight one of the codes and press F12 it will go to "freeze frame data" ...This is a snapshot of speed,load, temperature, RPM, number of faults counter ect. at the time the fault occurred and can be very valuable... So if you have not got this data I suggest you drive again unit the fault occurs and get this data.....then we will go from there.....but speaking simply from decades of experience , when the "rich limit is reached" it is a vacuum leak is 99% the cause and when the "lean limit is reached" a bad MAF sensor is 99% the cause... BTW : you did buy a Bosch MAF right ? not a knock off brand......

Quotes source post: 19946817

Interesting. Yes Bosch, not knock off. Two different ones since they can be suspect. Might have to do a piwis to find out because durametric doesn't tell me whether it's rich or lean limit exceeded. I assumed it's rich since the RKAT value is negative meaning The computer is trying to decrease fuel to reach Target values. Is there a way for durametric to indicate rich or lean limit? The numbers that r posted are what show s the same day the check engine light goes on and without any reset. Engine off , in the garage as soon as I get home and grab the durametric .They will basically stay the same with RKAT below zero indefinitely unless I do a reset and clear codes with the durametric. I have used the original maf and two new ones. Total of three different ones. I will reevaluate but to my knowledge they are real deal from FCP. Also smoke tested twice because there was a cracked oil fill tube that came with the car years ago. At that time the RKAT did suggest air leak that resolved with fixing the oil fill tube air leak. Could it be an air leak if the RKAT is pulling fuel?

Quotes source post: 19947926

Does your Durametric have "freeze frame data " ? ( the data collected at the instant the code is set...) I don't trust anything but PIWIS when it comes to fuel trims and codes pertaining to mixtures ......The fuel trim strategy on Porsche is different from any other manufacturer I can't get past your tester saying the RKAT is only 1% but you are setting codes for RKAT exceeding limits on both banks.... As a test/experiment you can create a large vacuum leak with engine running and watch the RKAT for a few minutes to see how far it changes before the code is set ....

Fun! Will do. Might be a day or two.

Quotes source post: 19927667

have ya checked your FPR?

Quotes source post: 19948836

Good question. I kind of dropped that topic since it wasn't raising any eyebrows when I mentioned it. I also searched it and didn't find much. So, I have no idea how a fuel pressure regulator works but I have been thinking about it. Here's what I gather. Correct me if I'm barking up the wrong tree. They have a diaphragm that is actuated by a vacuum line. Their purpose is to increase flow when intake manifold vacuum increases because the engine is under load. If the diaphragm fails and gets a hole or tear, which can happen eventually, two things might happen. First, fuel can pass through the diaphragm into the vacuum line and then into the intake at the other end of the vacuum line. Unplugging the vacuum line at the fuel pressure regulator with the engine running would result in fuel leaking out of the fuel pressure regulator port. I have unplugged the vacuum line at the fuel pressure regulator and didn't get any leak or change in idle but maybe I should try that again. Second, if they are intended to increase flow at cold start would it make cold starts more difficult, a problem I don't have when cold but occasionally when warm? In fact, when I have that problem with a warm engine it reminds me of a partially flooded/ loaded up motor that clears if I can let it sit briefly, then get it running and moving for a minute or two before it normalizes. Is that symptomatic of fuel pressure regulator fault? How do you test? Does the fuel pressure regulator increase fuel flow at the injectors/ fuel rails at startup? Do they get replaced as preventative maintenance at specified intervals?

FPR is the other way around, it decreases pressure at high vacuum and is highest pressure with no vacuum. There should be a spec for fuel pressure at idle and a different spec at idle with the vac line disconnected. Checking those 2 pressures will confirm the FPR is working properly.

Quotes source post: 19950232

Oh, yes, of course. Makes sense. So decrease fueling when closed or partially closed throttle when there is high vacuum and allow full fuel when the throttle is open. Maybe this would give me a rich mixture at low RPM and lean mixture at higher range RPM. Have to check fuel pressures when I get back from spring break skiing after next week. Still don't know why I would have a check engine light with only mild changes in RKAT.

thanks guys. I replaced the fuel pressure regulator to eliminate that variable and replace a 25-year-old part/vulnerability. There was a small amount of fuel in the fpr vacuum line so does that mean there may have been a perforation?

Quotes source post: 20183463

The fpr has a connector part that connects to the vacuum line. If that part has petrol or smell of petrol, the fpr is bad.

Quotes source post: 20183474

Yes, it had a few drops of fuel in the vacuum line which should be dry. Not sure how that would make the car run rich however I think this can be a cause of engine fires. It's not expensive so replacing it made sense.

For those who wonder, Fpr lives down here.

Quotes source post: 19950232

In other words a faulty fuel pressure regulator might allow too much fuel at idle/ low RPM?

Quotes source post: 20184147

If fuel on the vacuum line, it will burn as well, making the mixture more rich. Vacuum is the engine sucking air in. If you are lucky like me (in a VW golf in the past), you can also see flames at the exhaust...

Better than flames in the carburetor like occasionally in my old Volkswagen squareback. Real thrill to be on an LA. Freeway with that. Pictures of the fuel pressure regulator for anyone wondering. push lines aside to see the location on the right in the engine bay. And, there it is, with corresponding vacuum line.

Quotes source post: 20184955

Are there 2 fprs or just one? One on each bank I mean

Yes, the pressure regulator is likely your cause of erratic Fuel Trims... With Liquid Fuel on the Top side of the diaphragm it will restrict the function of the Diaphragm ( which is to lower Fuel Pressure at Idle).. That is why while driving sometimes and stopping for Red-Lights.. you would set a Code for Rich Rkat...then by the time you got home and hooked up the Durametric... the Diaphragm had had time to finally lower the Fuel Pressure/Fuel Trim/Rkat... A simple fuel pressure Test with and without vaccum line connected would have found this...

Quotes source posts: 20185194, 20185222

Just one that I know of. As pictured above. Glad I replaced it. There was a bit of fuel in the vacuum line and that shouldn't be there. I think it can be associated with engine bay fires. The fuel trim numbers haven't changed at all when checked after driving. I'll watch a few more drives. It still can occasionally have trouble on warm start up, bogging until it gets moving. Never a problem on cold starts and it clears within a minute if it gets up to speed. Did anyone else have that symptom?

Quotes source post: 20196072

After a repair it is always a good idea to clear the error codes and subsequently reset the values... Do that as it may relate to start up. And check for vacuum leaks

Quotes source post: 20196290

Yes, good strategy. I clear codes and reset the trims periodically as things get changed to evaluate for improvements. The ecu then adjusts and revises fuel trims over multiple drive cycles. It seems like 5 to 10 runs before the effects are fully expressed and coming to a steady state so takes some time to know if the car isn't run daily. As for leaks, in a recent PCA video Jake and Vinh say that vacuum leak such as a crack in the oil full tube will result in a rich condition which is the opposite of what I understood. Is that true ? Seems like an air leak would cause a lean mixture, especially at low RPM.

They say it will run rich with a vacuum leak at the oil tube. Is that right? 38 minute mark. You Tube

Saying that a vacuum leak will cause rich mixtures is not technically correct... The closed loop system is designed to run at 14.7 AFR/Stoich/Lambda 1 for the best operation of the Catalytic Convertor...( Emissions) When you have a smallish vacuum leak the AFR will go up ( above 14.7 to 15+) ie Lean,, the Oxygen Sensor detects this and the DME will increase Injection Time/Richen Fuel Trim to bring it back to 14.7 AFR/Stoich/Lambda 1...............so not really running Rich, same AFR as before the vacuum leak .. If it is a big vacuum leak..the System can't even correct for it and for sure will run lean.. But ...If you have an injector that is partially stopped up running lean, The Oxygen Sensor will see this and the DME will increase Injection Time on all 3 injectors on that Bank untill it reaches a 14.7 AFR "average" which means 1 cylinder will be leaner than 14.7 AFR , and 2 cylinders will be Richer than 14.7 AFR... And Vise-Versa if an injector is leaking fuel ....

Ok. Thanks for your clarification. So RKAT will be positive to compensate for air leak/lean condition with oil filler tube vacuum leak. That was confusing. I'm not looking for an air leak in my case because I've got negative RKAT trims. My injectors are being turned down, fuel is being pulled because my motor is running rich and needs less fuel. In addition I've smoke tested. I replaced my injectors with 996.2 units. It looks easy if you remove your engine but kind of fussy with the engine in the car. This made only minimal improvement subjectively and did not affect my fuel trims so this makes injector problems unlikely in my case.

Quotes source post: 20301353

Yep

Good. That makes more sense. I don't know what they were thinking in that video. I'm wondering if a bad coolant temperature sensor could contribute to running rich. If it isn't working properly and the ecu thinks the motor is cold will it add fuel and run rich? Coolant sensors are cheap and mine is likely original so getting a bit old at this point.

Quotes source post: 20302240

Sometimes smart people will say things that are not "technically correct " just to get Lay people to understand a tricky concept of how one particular something works... Yes a vacuum leak on one bank will cause the Fuel Trim on that bank to go "rich" but the engine is not running rich, it is merely compensating for the lean condition.....just a tricky word symatics. Your RKAT is showing it is adding Fuel on Bank 2 ONLY, meaning there is a vacuum leak/lean condition on Bank 2 .... A Coolant Temp Sensor would effect both Banks....

Actually, I apologize, they are quite similar. This is with engine off so it is a stored value but I don't think that matters. Correct me if that's not true. RKAT on both sides is negative indicating injectors are pulling fuel to compensate for slightly rich fuel mixture. This may not be enough to trigger a code. 1. Should it be concerning for cylinder washing? 2. Could it be related to a faulty temp sensor and result in bogging when starting a warm engine? Sometimes it causes a few misfires until the car gets moving...

[Image-only post; no author-written text. Original image references:] https://cimg5.ibsrv.net/gimg/rennlist.com-vbulletin/2000x1575/markup_1000009582_0ab925024554cc63a0d0f8612571020c3abab12f.jpg

@Otto Bonn I get that 'bogging down' or rough low idle when starting a warm engine. Have done since buying it. A couple of blips of the throttle and it settles. Watching this thread now...

I think you are trying NOT to find your problem , or are too casual at running down the issue....or have fixed the problem and don't realize it.. It's not possible to have good RKAT values and also have Codes P1133 P1126 ..... Are you still getting Codes P1133 P1126 ??? If so, you need to check Fuel Trims as soon as the CEL appears..... There is also "Freeze Frame Data" that can help with certain cases as it shows the time, speed, engine RPM , load, ect when the fault occurs... To access Freeze Frame Data, just highlight the Code then hit F12

Quotes source post: 20302889

Thanks for helping me think it through. It's true I'm guilty of being crazy busy most of the time, but still trying to work things out. I have learned a ton along the way but it's a tiny fraction of what you and some of the others here know. Here is the recent durametric from the CEL after replacing the fuel pressure regulator, clearing codes and fuel trims. It's a little bit cryptic but always the same codes and similar trims stabilizing near these values now that my oil filler tube air leak is fixed, MAF is replaced x 3, injectors are upgraded, fuel filter is new, and FPR is replaced. My interpretation is lower load range means low RPMs. Is that correct? How much can a coolant temperature sensor effect these symptoms? Probably not? I'll have to look at capturing data with F12, that's new to me and could be helpful.

Do you also have the $75 PIWIS ?.............. I don't like using Durametric for Fuel Trim Diagnosis...... Your Tester shows % for FRA but not for RKAT ... I think the Durametric shows "Lambda 1" for RKAT ....you need to verify this if your going to use Durametric ... Have you tested the Fuel Pressure ? Those 996.2 injectors may be your issue...they flow about 10% more than the 996.1 injectors ( may be within range if you run E10 Fuel)

Yes, correct, it's durametric. Although changing injectors seemed to improve things it was only subjective and the fuel trims were not affected. Still good maintenance to have them done. I've been running ethanol free tier 1 fuel exclusively for some time and wanted to exclude that as a factor. It's not clear why there is a CEL for trims that you consider minimally deviant from targets of RKAT =0. Maybe these are false CELs but they sure are consistent. There is also the question as to why there is frequent bogging and stumbling with restarting a warm or hot engine. I'm going to do the coolant sensor just to spend $30 and cross it off, not really seeing many posts about that helping but part of a systematic refresh of old components.

I agree, the fuel supply needs a look and will get evaluated next. Maybe a trial of E10 gas but one thing at a time and it seems like the system should adapt either way. Overall the car does quite well and we have a ton of fun driving it. Sunday was spectacular and my son pretty much begged to get out for a drive. Well, sounded good to me and wanted to check fitment of my E88s with new lips so my wife sent us on our way...

[Image-only post; no author-written text. Original image references:] https://cimg7.ibsrv.net/gimg/rennlist.com-vbulletin/1180x1425/markup_1000009738_bb6b7e32f663747f1f456e8aacdae2a63b01a97e.jpg

Well see here is the thing...I'm good at Diagnosis of Fuel Trim as that was my Forte for 40 years, but I'm better with PIWIS as that is what Porsche uses and I know Exactly what to expect from it .....Durametric not so much... On the 99 model Porsche/PIWIS uses TRA for near idle Trim and the limit is +/- 0.36ms....on later models Porsche/PIWIS uses RKAT % and the limit is +/- 6%....but on the 2000 model I'm not sure what Durametric is using... It looks like it maybe Lambda....If it is Lambda then 1.31 = 31% You can check/test this by clearing the fault memory to reset to 0 , then run the engine and induce a large enough vacuum leak to keep increasing the RKAT value ( while watching the Durametric) untill you get the CEL/fault code... Using E10 will lean the mixture.......using "996.2 injectors" along with "ethanol-free" may just put you out of the DME adjustment window !!! And yes it doesn't hurt to know what the fuel pressure is ... P.S. :: and the hart to start/hic-up when warm may be fuel pressure dropping to fast hot due to a leaking check valve

https://rennlist.com/forums/996-foru...-to-start.html This thread mentioned a faulty coolant sensor thought to be causing warm startup problems.

Quotes source post: 20304189

Probability %..... Of Coolant Temp Sensor failure 1% Of fuel pressure check valve failure 90 % You do what you feel is best ..... P.S. :: and don't forget the Purge Valve also has a high probability of failure that can cause hot starting issues ..

Quotes source post: 20304222

Does that coolant temp sensor also drive the water temp gauge? If it does wouldn't that tell you if the sensor was playing up? or are there different sensors...

Quotes source post: 20304227

Well, there are actually two Sensors built into one "housing" ....One Sensor the dash gauge,..and a completely separate Sensor for the engine coolant to DME...but they are both in the same Housing with separate wiring ...

Yeah, seems unlikely to be coolant sensor, I agree. Got the fuel level down close to empty after my drive. Having a look in the tank has been on my list for a while and Aaron the prof says it's so easy to pull the fuel pump that he's done it on the side of the road when necessary. Armed with false confidence I got a wild hair before dinner and had at it. Dusty like a mummy's sarcophagus, don't think anyone's been down this way in a while. Maybe not ever. Giving it a quick toothbrush wash before possibly dropping debris and tools into the abyss when it gets open.

The lean condition at higher RPMs has made me suspicious that there may be a rupture of an in tank fuel line. Can't see jack so I took random photos. Reviewing it afterwards. Is that the check valve?

There were five or six shots like this and they seemed like they were pretty much useless. And it's not the time to pull the whole octopus right yet, just not quite that psyched at the moment. Encouraged to get this far but elected to close her up to contain fumes. Last photo. Well, will you look at that? Different angle. Looks like a split, not that I didn't walk past it at first.

[Image-only post; no author-written text. Original image references:] https://cimg1.ibsrv.net/gimg/rennlist.com-vbulletin/2000x1258/markup_1000009806_1__005a2b7632e74c6d27617068a4600b4d7842f298.jpg

Excellent work, Otto!

It's clear that this could be contribute to high RPM fuel starvation. Now it's not so clear if there is a single problem or multiple problems. So either: 1. Ruptured fuel line effects both high RPM as might be expected and low RPM ranges somehow in a way I don't immediately understand. 2. A second problem results in low RPM Rich fuel mixture condition with ruptured fuel line affecting the higher RPM ranges.

The elegant simplicity of this fuel pump octopus is overwhelming. It's going to take some work to digest exactly what's going on here. Quite the tangle.

Clearly a not so uncommon problem. Poached this. It appears to represent the pump, venturi's, etc. Oftentimes the entire pump gets replaced because of failures in the tubing not the pump. New version of pump and tubing on the left, old version on the right.

This is useful. https://www.6speedonline.com/forums/...ictures-4.html Red to fuel injectors, blue from return, yellow and orange to and from Venturi siphons in the c4 tank. So basically it's the black return to the fuel pump that is split, decreasing returns to the fuel pump and the branches to the Venturi siphons. Looks like it is split in this example picture also.

The soft black rubber fuel line can be replaced with gates submersible fuel line but those fail. The new fuel pumps don't use black rubber. They are now all translucent white. PTFE lines are recommended. Is that what these are? Or just nylon? What diameter and lengths are needed for replacements? Discuss... Cheers

Amazon sells the accordian hoses in all sizes. Measure the diameter and order the length u need. I did this for a failed rubber line in my gt3 set up. Its a common issue as these cars r getting older and sit with ethanol mixed fuel.

I stupidly changed that with ordinary fuel hose which lasted 3 days. Then I used the submersible fuel hose. Still working 4 years later. Although I originally used Oetiker clamps which kept sliding off... ask Brad as I pulled out the pump at the track in Palmer after he rescued me with his trailer. Then the Oetiker clamps came loose again at Lime Rock. I replaced them with fuel injection clamps and no more problems.

Quotes source post: 20305801

Cool, thanks. Did you replace the rubber line as well as the other accordian lines? Looks like some threads claim they are all likely to develop micro fractures with time.

Here's a nice thread from the turbo guys. https://rennlist.com/forums/996-turb...etimeso-2.html Measurements of the individual runs are listed. Looks like 5/16 OD tubing, (is that 8mm?) I can't read what else it says. Is it easy to bench test a check valve?

Quotes source post: 20306172

I only replaced the rubber line but all can be done. The hose is cheap. From memory 8mm(5/16) sounds correct.