Can bad gas cause CEL and multiple misfires plus mechanical noise?

I had my '02 C2 at the track last Saturday where it performed flawlessly all day. The drive home is about an hour from the track and the car behaved normally along the way. I was running very low on fuel about 10 miles from home so I stopped to fill up with 92 octane at a 76 station. About 10 miles and 15 minutes of run time later I was stopped at a light and idling normally. When I took off the engine stumbled - the first time that's ever happened with this car. It recovered, but moments later it stumbled repeatedly and threw a CEL. I got the car off the road and shut down in a parking lot within 30 seconds at most. By then it felt like at least a couple of cylinders were down and it was making quite a bit of mechanical racket that didn't sound healthy. I fired it up briefly the next day to confirm that it was still in the same state, and to get it moved into a better position to be towed. It was still making significant amounts of mechanical noise which seemed to have a consistent pattern to it, as opposed to just cat converters randomly rattling from a shaking engine. I had it flat bedded to an indy shop who pulled the CEL codes which showed that all were related to misfires. No leaks or obvious external issues. We drained the oil and there was no intermix or metal shavings. The current engine is a rebuild with approximately 8K miles on it and an upgraded IMS and RMS. The indy hasn't had a chance to dig into it further yet and that's all the info I have at this point. So, my fingers are crossed that bad gas may be the culprit for the sudden onset of misfires and the resultant unsettling mechanical noises. Other possibilities are that a day of exuberant track driving may have loosened something up that happened to let go later on the drive home. I asked the shop to check for mechanical over-revs but haven't heard back on that yet. I understand that the cam chain gears are pressed on to the intermediate shaft and there is no keyway to lock them in place, so slippage is possible under the right (extreme) load conditions which would throw off cam timing and cause similar symptoms. Still, you'd think if something like that happened it would be while being hammered at the track, not when easing away from a light. Thanks in advance for any thoughts or advice on this.

It very well could have. I had a similar issue on an M3. Buddy of mine also filled up at that same station on the same day and got similar issues. I put in some BG44k and ran the tank empty and put in Shell and never a problem after. Fingers crossed for ya

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If any cam drive/driven sprocket moved around chances are the engine would be locked up. Thus with the additional engine running time -- which if things had been serious might have made them even more so -- and the absence of any scary things in the oil/filter and with no error codes other than related to misfires, bad gas has to be one of the prime suspects. Or the tank might have had something bad in it already -- maybe a bit of water -- and the low fuel level stirred this up coupled with filling the tank and the pump ingested some and sent it to the engine. The hard running might have put some plugs over the edge, or even loosened some valve/combustion chamber deposits which could have fouled a plug or two or even interfered with some valves closing fully. Sincerely, Macster.

Thanks for the input Macster and Tim. The repair shop won't be getting into my car until Friday. I'll report back with the findings once I have them.

Good luck and keep us posted!

Update: Report came back from indy today. 90% leakdown in cylinder #1. They slid a little camera/scope into the cylinder to look around and found that there is a small chunk of metal embedded in the cylinder head adjacent to one of the valves. It's supposedly a little larger than a spark plug electrode, but the spark plug from that cylinder was intact. It remains to be seen what the source is but clearly something internal broke free. I'll head over there Monday to take a closer look and discuss options. Anybody have an inside line on great deals for an X50 3.6L motor as a replacement?

Correction: Possibly looking for X51 3.6L engine as a replacement. (X50 was option code for the Turbo version)

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That's bad news to say the least. Not what I would have expected. So many times misfires are just nothing serious nothing worse than bad gas or bad coils, but there are exceptions and unfortunately this appears to be one of them. It would be very interesting to know what that small chunk of metal is and where it came from. That is a failure mode that is AFAIK rare, that I've not come across. (The usual source of foreign objects (so to speak) in the engine is a chunk of cylinder wall material breaks away or a valve comes apart after a (usually) a misshift with a subsequent very high overrev event.) For a replacement engine check with the several online Porsche parts suppliers/resellers. Sometimes they have an overstock of engines and one can be had at a discount though the likelihood of this diminshes as the car model ages. As this happens the stock of replacement engines drops and replacemente engine prices go up. But check. Best of luck. Sincerely, Macster.

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Im really sorry to hear this... This sucks... Glad to see you are sticking with the car though! Call Flat 6 innovations. Jake Raby. I have had at-lengths conversations with jake and I have to tell you these guys I feel know the engines better than Porsche. They also have kick-*** from the ground up builds....

Thanks Macster and Kyle. Flat 6 is one of the options under consideration at the moment. They also appear to be by far the most expensive option. The rational part of my brain is having difficulty justifying a repair cost that is sneaking up on the replacement value of the car. That being said, I didn't buy this car as an investment or with the thought that I'd get my money back out of it. I bought it because I love to drive and this car pegs the fun meter. I'll post updates once I get a little further into this, both in terms of failure diagnosis of the existing engine, and details regarding the experience of getting it back on the road again with a motor that is robust enough to be well suited for both street and DE track driving.

Who did the rebuild and how long ago? No matter the time, 8k is not a lot of miles for a failure.

Rebuild was done in early '09 and had about 3K on it when I bought the car Nov 2011. I've never seen anything but positive comments about both the shop in SoCal and the person that built this motor and I've talked with him since the failure occurred. Seems like a good guy with a first rate background. I don't want to say anything here that may undeservedly tarnish a good reputation, especially since the motor has not yet been torn down to determine the cause of failure. If it turns out there were obvious shortcuts or shoddy parts used that would clearly compromise longevity then I will absolutely name names.

Any results on what exactly caused the failure of the "new" rebuilt engine from this car? Very curious.

I think the cause of your failure will be in this statement. Is there a warranty on the engine? What were the upgrades? If no warranty, there are several low to mid mileage 3.6's from salvage cars for sale. Even some of the recent flooded cars will have repairable engines. These may be options if yours is a CEF total loss. I assume by the avatar, you replaced the car. but could you update if possible. Surely you have an answer by now? This information is useful to others. Feel bad for you, sorry. Found the other thread but still dont know what you did.

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You have a good attitude about your engine misfortune, hope the rebuild or replacement motor fixes your problem, and if there was a fault found in the last rebuild, that a suitable remedy is found. GL