My CEL does not flash, it comes on and stays on. When this happens there is no change in the engine performance. The only way I know the CEL came on is the warning chime and the light of course. I've ordered a new fuel pump and well change that out. I was hoping to do the fuel filter, but I'm told the filter is part of the fuel tank. I do not plan to spend $2500 for a new tank to get a new filter. If someone knows something different, please advise.

Also, when the dealership had the car, they did a leak down test and it passed, all cylinders were within spec.

I talked with a Porsche mechanic at the track last weekend. After describing the issue, he said it was probably the flywheel, but also advised to change the fuel filter due to the mileage on the car. He also claimed that the filter was on the bottom of the pump.

 

Here's the latest update on this problem. I've replaced the fuel pump. The pump does have a small filter attached to it. Anyway, the wife drove the car to the doctor's office and the CEL came on. Same problem as before. Cleared the code and drove it some additional miles, so far no problem.

Any ideas?

 

Fuel pump did not fix the problem.

I have now replaced the crankshaft position sensor. Drove the car into town. On the way back I mentioned to my wife that the problem seems to be fixed. No sooner had I completed the comment, the CEL came on. I think the car is listening.

While at one of my last track weekends, I was talking to a Porsche mechanic from an independent shop. After he listened to my story, he simply said it was the flywheel. That the flywheel is just slightly moving causing the CEL. He claims he's seen this before and replacing the flywheel fixed the problem. Unfortunately, I don't have the tools and know how on tackling this problem. The independent and the dealership quoted the same cost; about 4K. I figure while the flywheel is being replaced, might as well do the clutch and RMS/IMS bearings.

 

Just out of curiosity, did you replace the CPS with Porsche OEM, OE, or just aftermarket? On older Porsches there can be issues from general aftermarket sensor; the same thing has been observed on BMWs that I'm familiar with. I can only imagine that more modern cars would be more susceptible to not-quite-OEM spec sensor inputs.

The other thing to think through is the whole system involved in ignition. You've pretty much ruled out spark (with new coils, twice), and started in on fuel. Is your car direct injected, or is there a fuel pressure regulator in the system somewhere? If port injected, have you checked your fuel pressure?

The last major component in ignition is air: how your MAF? If that's sending weird signals then what the DME reads as an output via the O2 sensors may cause an issue. I don't really know, obviously, since I don't think that @harveyf question has really been answered, about what exactly is causing the misfire error to be reported. Is there an EGR system on these cars that could be contributing? That's also something that would be getting turned down or shut off as the engine gets warm.

I really don't think that you need a new engine. For all of the great engineering and close tolerances in these things, they're pretty straightforward pieces of machinery. Perhaps I missed it, but do you have a PIWIS type reader? I don't, so maybe this is not actually a useful suggestion, but my impression has always been that PIWIS was pretty good about giving more information than just the error codes. I don't know if the dealer shared any of that with you when the car was with them.

Good luck with all this

 

The guess/theory is sound. Only other thing you could do is look at some live data to see if anything is strange but to also see if there is a pattern as to when the missfire is happening. I'm not sure if Porsche provides freeze frame data when the it those a CEL. Only other thing I could suggest is taking a look with a borescope through the hole of the removed crank position sensor to see if anything is wrong while someone slowly bars the engine over. It may not help you fix the problem but it could help confirm where the problem is.

The people on YouTube I see diagnose these problems usually ending up using something like a PicoScope. That is an expensive tool that requires a lot of know how to correctly use and interpret.

From my knowledge it is the crank speed. Those hall effect sensors are mighty accurate and pick up tiny fluctuations in crank speed. Computer does computer things and detects anomalies. That will count as a misfire in the misfire count in the live data. A misfire is not enough to throw a misfire code, you need more. I'm not sure what Porsche's exact code set criteria is for that.

I think your point about using an OEM sensor is a very valid one.

 

My reading indicates that mis-fire codes are based on the firing pulse digital signature of the flywheel teeth, as read by the CPS and interpreted by the ECU. If the flexible part of the flywheel was starting to fail, I guess I could see that the digital signature was being degraded enough to throw a code. Porsche does describes it as a "learned" digital signature. I would be tempted to do a cold reboot on the ECU (disconnect battery for a while). I have not been following the thread but a new CPS would be the cheap ruleout and a new flywheel would be the expensive route. Before I jumped into that process, I think it would be worth it to get the car to a dealeship for a workup. Heck, none can be more than 24 hours away in Texas The right guy with the right equipment should be able to give you a good diagnosis.

 

Just to throw this out there, one user had issues with a misfiire on all cylinders due to a replacement engine belt. He had a non-OEM and it threw all sorts of misfire codes. After going through the same thing as you (plugs, wires, etc) he replaced it with an OEM from the Porsche dealer, and it all went away. I think that was on a 981, but you never know?

Did you recently replace the belt? Possibly with a non-OEM?