P300 Misfire...P301/P302/P303

Alright, so I have a MY03 C4S 54k miles. Got these CEL for misfire. Spark plugs were only 10k old, but went ahead and replaced all coil packs and spark plugs. Old coil packs were in rough shape. Cracked and some rusty.... Anyways, I cleared all CEL and everything looked good, until this afternoon when the car threw the same CEL. Only 25 miles after replacement. Coil packs and plugs are brand new....what are the chances that 3 coil packs failed on the same cylinder...not likely. I have seen posts saying it could be a bad MAF, scored cylinder walls, bad intake lifter, gremlins.... What would you recommend here? Take it to a shop to diagnose or is there anything else I can check? For example run a voltage test on the MAF if possible? Any advice would be great, I'm no expert here.

finally found similar post: https://rennlist.com/forums/997-foru...s-4-5-6-a.html No answer to his specific issue....

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Taking the car to a (good) shop would be high on my list of things to do. If the misfires are not addressed by new plugs and coils and you are sure the right plugs were used (and by right I mean the specific plugs called for and not just some plugs a reference chart listed as the right plugs to use) and the plugs installed correctly (which means *no* anti-seize among other things) and the coils are installed correctly you are dealing with something deeper. Could be a MAF but a MAF is pretty expensive a part to throw at the symptoms. Do you hear valve chatter concurrent with the misfires? If so this can be the intake lifters. They can get "dirty" and not work properly, at least in those cars that have VarioCam Plus (variable intake valve timing and low/high lift). I seem to recall one or two cases of impossible to track down misfires that were found to be due to a failing dual mass flywheel. An even more expensive part to throw at the symptoms. I vaguely recall there can a failure (at least a problem) with the fuel system of the car that can cause misfires. The C4S has that infamous dual basin fuel tank -- like the 996 Turbo -- and each basin has a siphon jet to pull fuel out the basin. The fuel tank is a bit of snake pit of hoses/fuel lines and if a hose develops a leak this can result in the fuel delivery to the engine being affected and misfires are a possible result. If the system gets worse the engine runs out of fuel at about half tank as the siphon jets no longer siphon fuel. Are you sure you read all the codes? Are there any pending codes? If the VarioCam solenoid/actuator acts up the DME will adjust fueling on the affected bank to try to get the O2 sensor readings it expects. In some cases the DME can adjust the fueling so far as to cause the engine to misfire. If this is happening you can see this -- so to speak -- by monitoring fuel trims using an OBD2 code reader/data viewer tool. There is also a possible problem with the DME. This is quite rare though and before messing with this I would exhaust/eliminate other explanations. Lot of possibilities. Unfortunately just possibilities. Some professional investigation is needed unless you opt to toss say a MAF at the behavior and happen to get lucky.

I would suggest taking it to a shop because single bank misfires is usually challenging to diagnose if coils and plugs have already been eliminated. You can use a generic scanner to read the MAF and fuel trims to see if anything jumps out. If you have Durametric, you can check for other readings such as cam deviations. A good Porsche shop should have the Porsche scanner that can run tests to eliminate or confirm the variocam+ operation and sticky valves. They can also check cam timing and any air leak on bank 1.

You might find this interesting...same codes and some diagnostic information. Two things stand out - Variocam on that bank, and the O2 sensors on that bank. The O2 sensor(s) kind of make sense for your codes on a particular bank because that would affect all cylinders on that bank. Likewise with the Variocam activator on that bank. I think a full scan and diagnostic readout from Durametric or PWSII would help you locate the problem. It might be as simple as a bad O2 sensor. http://www.renntech.org/forums/topic...-this-morning/

A friend of mine with a 997 Carrera S had these errors. here is the procedure we went through on fixing it. Initial error codes at first diagnostics. P0492 secondry-air sustem bank2 P0491 secondry-air system bank1 P0300, P0301, P0302, P0303, P0304, P0305, P0306: which are misfire on sylinders cleared error codes with durametric restarted, got misfire on P0301, and P0491-2 cleared with durametric swapped with my maf restarted, got misfire on P0301, and P0491-2 opted to replace all coils and spark plugs restarted, got no error messages, everything is fine So the lesson learned is that one faulty coil or spark plug might (over time) create additional error codes. None of the error codes has reappeared. And, always replace all coils, this also applies for spark plugs, not just replace one that you think is faulty.

All I get are the misfires on the one bank which leads me to believe its a device like an O2 sensor or fuel delivery. Once again, I am extremely new to the M96 and generally not a gear head. I'll make an appointment with Mraz in WI to review the problem. All ODBII codes were misfires. Nothing else. The CEL flashes for a second then goes solid until I reset it.

Thanks for the replies! I guess the PDX will have to wait this weekend.

Update: A local mechanic friend of mine took a look at it and was able to eliminate the O2 sensors. Unfortunately, he is not an import mechanic and far from a Porsche mechanic. He found that cylinder 1 consistently throws misfires. Cylinders 2 and 3 are more sporadic. His thoughts since its at idle is that is a valve issue. Does any of this lead you to a different line of thought? I may just have the Porche dealer take a look too.

I am moving ahead with replacing the AOS shortly since I have it in hand and this will help eliminate this line of thought. While I am in there does anyone have specific instructions on how to do a intake leak test?

Macster, keep the suggetion to one maybe two theories. Throwing everything imaginable doesn't help.

I think your thought process of having the Porsche dealer check it out is a good one. They can diagnose it much better and probably pinpoint the problem. Also, if proceeding on your own I would suggest investing in Durametric. It is not cheap but will help you diagnose and confirm what is happening to throw those codes. It is better than throwing $$ at replacement parts. With all that you have done so far, now I am leaning towards the Variocam solenoid/activator on that bank. Good luck!

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Does the Variocam actuator play a factor while the car is at idle? I thought the actuator only operated at 3000+ RPM's?

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If it were the cam actuator it should be throwing a 1341 code. So Mraz threw their hands up?

I thought you said you were driving the car thus running it up and down the RPM range when it threw the codes. No, I don't think the Variocam solenoid/actuator will come into play at only idle. But having said that, a sticking actuator can create havoc at idle because it doesn't return to start/idle mode and the valve overlap is not right. Also, if I remember correctly, the Variocam does start to come into play at a low RPM (like 1400 or so) and backs off at high RPM. There are some good posts on the Variocam operation. So if you clear the codes, start up and just let it idle, does it still throw the codes? Remember, all this advice is guessing. Recommend getting it to the dealer/indy/Durametric for narrowing down the source of the codes.

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Didn't take it to Mraz, my buddy is an owner of Richlen Auto. Trying to find someone who doesn't bill by the book. They charged me for a full clutch service when they already had it out. Yes, sorry for the confusion. I will resurrect this post once I get a Porsche mechanic to give me some recommendations.

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That's exactly why I made my comment a while back about them. When I had my '67 911 I went to Dean at Fabson Fabson Engineering AG W63 N133 Washington Avenue Cedarburg, WI 53012 [phone removed] Or try Chris Schuh's shop http://www.csmotorsports.net/ Good luck!

I had a completly non operating variocam (fried driver in the ECU) and missfire was never a problem.

I connected a USCAN reader and was able to pull some interesting live data in regards to fuel trims. As I mentioned previously I am no mechanic, but I did spot a few things which caused my concern. The first image here shows long term fuel trim on bank 1 at 2.3% and bank 2 of 8.6% at 670rpm. Shorterm values moved around and usually remained consistent between the two. CEL Not blinking. Misfires not occuring during this frame. Second photo shows LT FTRM1 and LT FTRM2 the same, but notice now the short term ST FTRM1/2 went to 0% at 670 RPM. This data was collected while the CEL light was blinking, indicating that there were active misfires. Next post will include the same data captures while the car is at 2500 RPM. If the STFT immediately decreases and moves to acceptable levels and the LTFT slowly starts to come back down, I may have a vacuum leak, right? I also assume acceptable FT short or long should be near 0% in a healthy engine or at least be consistent between the two banks, right?

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I'm thinking you are on to something. Time for a smoke test?

Alright, a vacuum leak doesn't appear to be the issue. Both ST and LT fuel trims stayed consistent holding at 2500 RPMs. I assume this means I likely don't have a vacuum leak?

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Dunno...where is Ashai when you need em?

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Is there a can of smoke to buy or should I roll a fatty? Will this work or should I make a custom smoke machine? http://www.amazon.com/CRC-Liquid-Detector-Tester-Aerosol/dp/B001B3BL0S http://www.amazon.com/CRC-Liquid-Detector-Tester-Aerosol/dp/B001B3BL0S

IMHO, nothing jumps out of your FT's. Anything within +/- 10% is not bad. To verify if it's a vacuum leak, you can use a smoke machine or you can spray carb cleaner onto the suspicious areas and note any engine rev chance. I don't recommend the latter as it can get dangerous spraying highly flammable liquid onto a running hot engine. You can also check the RKAT value of Durametric, which is the LONG term idle fuel trim. Other than those, there's really not a whole lot you can go further. I'm sorry to say but you're completely under-equipped to diagnose this single bank misfires. Even for a shop, you need one with a Porsche scanner to run tests on the engine. The tests are quite involved and they test the variocam+ operation and try to deduce if some of the intake/exhaust valves are malfunctioning and if they are, the suggestion is to replace all of them on that bank. The other thing you can check is cam deviations but again you need Durametric. Sorry I'm not trying to be a downer but this is truly not an easy problem for DIYers.

[Image-only post; no author-written text. Original image references:] http://houstoncheapfireworks.com/products/large/Assorted-Smoke-*****-12-Pack-Smoke-Bombs-634922066668906250.jpg

Thanks everyone. I just bought a Mammoth smoke bomb to ignite in my airbox for the smoke test. Two appointments to review the problem this week and next. Getting two opinions.

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Not necessarily. A small vacuum/intake leak has a big impact at idle or just off idle, but a much smaller one at higher engine speeds. (Example: A leaking oil fill tube cap on my Boxster.) My info is when trims start banging on the 10% threshold that's a sign of a problem. I can add - hope I'm not going over my word limit! -- that I came across one Boxster owner with misfires on just one bank and he ultimately traced the cause of the misfires to a bad MAF. But a new MAF is an expensive part to throw at the symptoms. (In the case of my Boxster I threw a new MAF at the symptom - CEL + error codes -- and the CEL and error codes came back. Shortly after this I was looking at the car one evening with a co-worker and he heard the cap leaking with the rear trunk lid open.)

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You've squeezed in just under the limit!

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Any write up anywhere of diagnosing this with a Durametric?

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No, the procedures require the PST2.

Dup..deleted

Update: Mraz ran diagnostics on the Variocam and other systems and was unable to find anything out of place. All the timing and valves check out healthy. They are 75% sure the problem is with a vacuum leak through one of the cam solenoids. They took the seal off and noticed it moved too easily. He also mentioned another "spring," but I can't remember what it was for. Should have it replaced and re-assembled tomorrow by noon. I assume the solenoid seal is similar to that of a 996.1, but the 996.2 being on the inside of the valve cover. I replaced these seals on my last M96 only to find that the oil was leaking from the inside of through the solenoid wiring....

Well, it appears to finally be fixed. The culprit was the cam solenoid seal. Car drives much better, even noticed on start-up things are much smoother and at idle. Labor was 6 hours to disassemble and inspect the entire valve train and reassemble. A word to help other DIY'ers troubleshoot this issue. I had more misfires on cylinder 1 than 2 or 3. And Cylinder 2 had more misfires than cylinder 3. Watching these numbers could be strong indicator that the cam solenoid gasket is creating a vacuum leak since it is closest to cylinder 1. Going to run for a couple more days and get emissions test completed. Wish me luck!

This is the seal between the valve cover gasket and the solenoid?

Congrats. It also seems like you got a good mechanic. Good luck with the emissions.

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Here is the part. http://www.pelicanparts.com/cgi-bin/...0Valve%20Cover

Cool but i don't think it makes a difference that the seal is close to any of the cylinders. That part coincidence.

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The evidence backs it up, but I get it pressure being constant across all valves. I'm just an amateur conspiracy theorist. On another note, good thing I checked me oil, it was a quart low. Just checked it before taking it to the shop. I suspect when removing the valve cover there was some oil loss and they didn't top it off. Anyone know how much oil is lost by removing the valve cover? In any case, shouldn't checking the oil be the last check before turning it up? Disappointed to find this....

What pressure across all valves are you talking about?

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I understood him to mean that the pressure (or vacuum) would equalize in a chamber and not be different at cylinder #1 vs #2 or #3.

Diagnosis of Variocam solenoid seal leak : with engine running ,spray carb cleaner around seal. If it is a vacuum leak the engine speed should vary as the crankcase vacuum sucks in a combustible vapor. Alternatively slather grease over the seal to see if that temporarily seals the leak and causes idle smoothness to improve?

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That's a pretty good idea!

Praise indeed ! Sadly, I have spent so much time in that area of the engine I have very reluctantly become an expert in the myriad number of things that might go wrong. Diagnosing what really is defective is the trick I have yet to master. But it wasn't the transistor in the DME !Inside joke :-).Yes, I did check it!

Sometimes the simplest ideas are the best. However, I wonder the safety of spraying a combustible liquid near exhaust components?

AS long as the header and cat are not cherry red ,you are golden

Make sure that the new coil connections are on correctly. Pushed home I mean. I got a po305 (cylinder 5 misfire) from one of mine and a very quick CEL because I did not push the electrical connection fully home. It maybe something as simple as that and nothing wrong with your new coils. The new coils are wider than the old ones with new type screws. I find that the connection is slightly further away and harder to push home. It's very unlikely that 2 coils are bad.

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a small vacuum leak is not (sucked on ) as much when the throttle is open up as much as when the throttle is closed. Think of % wise. At speed maybe only 1% suction is created on the small leak, whereas at idle, vacuum is only able to suck via idle valve and the small leak. Now the small leak lets in 25% volume. I would say you have a very small vacuum leak that only shows up at idle. This vacuum leak is unmonitored by the MAFS. The O2 sensor lets the computer know and it compensates with more fuel in an effort to hit it's 14.4:1 'Stoichiometric' range. Eventually over compensating which can cause misfires. It costs you nothing to check out the lower rubber boot on your AOS from under the car. ( not the diaphram, you cannot see that, as that is inside the AOS) It maybe weeping oil and if it is, it can suck in air moreso at idle. Just a suggestion. Good luck.

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Hurdi thanks for the suggestions. This thread was resurrected. After replacing the solenoid bracket/seals the misfires went away and I passed emissions. She's been running great ever since. Prob 5k miles since repair.