Petersa9

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.

Petersa9

finally found similar post: https://rennlist.com/forums/997-foru...s-4-5-6-a.html

No answer to his specific issue....

Macster

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.

Ahsai

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.

DBJoe996

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/

Arne Klinge

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

1. cleared error codes with durametric
2. restarted, got misfire on P0301, and P0491-2
3. cleared with durametric
4. swapped with my maf
5. restarted, got misfire on P0301, and P0491-2
6. opted to replace all coils and spark plugs
7. 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.

Petersa9

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.

Petersa9

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

Petersa9

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.

Petersa9

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?

Imo000

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

DBJoe996

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!

Petersa9

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

Sneaky Pete

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

DBJoe996

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.