Porsche 1999 911 Cabriolet 996 Bank 1 Misfire

Hi All, Looking for some advice on a cylinder 1-2 misfire (All of bank 1). It misfires all the time (warm and cold) from idle to about 3000rpm. I've ruled out these possible issues... Spark plugs, injection coils, variocam solenoid, cleaned out my throttle body. These are the codes I get P0300, P0301, P0302, P0303. I'm not seeing any issues on bank2. My thoughts are that it has to be something common with bank1 for all the cylinders to be misfiring. My next test I think should be an air leak upstream from my throttle body. Is this common? Any ideas? Check out my TRA and FRA readings. Do these look normal?

New user, one post. Hmmmm... P0300 - general misfire code P0301 - misfire cylinder one P0302 - misfire cylinder two P0303 - misfire cylinder three All on Bank One How old and mileage are on the spark plugs and coil packs? If you clear the codes do they come right back? Check the plenum connections on Bank 1, make sure they are tight and connected correctly. Any recent work on the intake or plenums? AOS replacement?

I think it's interesting because my car has the same issues. I was hoping for some answers here, but there are a dozen threads on this topic and it seems like dozens of possibilities. You'll be seeing my inquiries maybe later today. The good news about this thread is that it looks like the poster has a durametric.

You write ". My next test I think should be an air leak upstream from my throttle body. " If you meant "testing for an airleak upstream" I think you can save yourself the effort since an airleak upstream of the TB would NOT confine its effect to bank 1. Look into cam deviation of bank 1 (and compare it to the number for bank 2) instead. If the deviation of bank1 is greater than +/- 6� (=specified OK/NOK limit) and Bank 2 is less, then I'd say you're pointed in the direction of a timing error due to a skipped timing chain by 1 tooth or worn cam chain pads (not sure what deviation either cause would yield as cam deviation).

Its a common issue with 996s Lots of threads on this In order 1. coil packs 2. sparkies 3. vacuum leak 4. vario cam bracket cracked or lose 5. bad gas (could be #1) 6. Stuck valve. Rare, but serval guys have posted after going through this long list chasing misfires valves were to blame. Again rare. 7. Long shot but my Indy shops swears oil can have an effect on misfires. Its a big shop, highly respected. From SUV Porsche to running a large fleet of 996 race cars he swears by 0W40. Said higher weight oil can have a negative effect. Never heard this anywhere else so I hesitate to post it but thats a direct quote. Start with the easy stuff. Like a bottle of seafoam or tectron. Be sure to clear codes!

Let me share a slightly different perspective with the exact same misfire codes I experienced last year on my 01 car. Started chasing the p0300, p0301, p0303 codes. Plugs, coils less than 250 miles on them, tested for vacuum leaks throughout the system- all tested perfect. Had my variocam deviations pulled, all within spec. Switched all 6 plugs/coils from opposing banks to completely rule them out. No luck all misfires remained consistent showing a cylinder 1 and cylinder 3 issue. These misfires occurred mainly when under load 75% throttle input, beginning at roughly 4,800 rpm. Don’t know if yours are load or rpm dependent? Finally after ruling out many of the basic items above, I decided why not pull the oil filter, see if something internal could be occurring. Sure enough I find ferrous copper bits in the filter and some in the sump after pulling that. Got it to my local shop to go in all the way. After full engine disassembly, we found a rod bearing was spun. (Had no knock to indicate this, which was more bizarre to me). Also surprised I was experiencing this since my vehicle isn’t tracked, and I’m religious with my engine warm up (2) time a season oil changes. Ended up doing a rebuild, got the bottom end in great order, magnafluxed crank, arp rod bolts, all new main and rod bearings, vario cam pads/ chains, sensors, chain guides, chain tensioners, lifters, fuel injectors, oil cooler etc the list goes on and on. Cylinders showed no signs of bore scoring, on my 3.4 car. Oddly my 01 car was fitted with the earlier pistons with the ferrostan coating and the dual row ims. Engine is original to the car which I can confirm. DT40 oil only from rebuild on. This is a worst case kind of scenario above, Don’t know if you’ve pulled your oil filter but it would hurt to have a quick look just to rule out anything more serious like my issue above. Double check that your AOS is also in good working order, and consider a future upgrade to the UAOS to eliminate the headache of AOS failure. Keep us posted. I hope you get this resolved.

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Ferrous copper?

I find it quite remarkable that your TRA for both bank 1 and bank 2 are at a perfect 0.00 !!!??? This is NEVER going to happen, unless you had just previously cleared the fault codes. Try running the engine some more to get TRA readings, they will also tell you if you have vacuum/air leak on a particular bank.

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Skip, FWIW, after replacing all four O2 sensors and MAF, these were my TRA readings on my '99 C2. I don't remember if I had recently cleared any codes though.

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Yours is a little more believable with -0.02 on bank 2.Anytime I see 0.00 it is a suspect value. If you want to see if the fuel trim is working just take the oil cap off while running and watch the changes...lol.. I bet yours is not 0.00 on bank 1 right now...

Can you post O2 sensor voltage values as well. Typically 0.00 is an indication of failure of something else unless those trim values were just cleared. ps. That 1.26 FRA on bank 2 is most likely a vacuum leak.

As someone with a similar problem and a Durametric this is a good thread to be jumping on. I know this has all been discussed before, but it's good to have the conversation again. Thanks for the insights. I don't know what TRA is, but I found this thread. https://rennlist.com/forums/996-foru...at-values.html Thank you Porschetech3 for all your shared knowledge!

The codes come back pretty much immediately. Coil packs have about 10k miles (I've swapped them with around with bank 2 and no change). Spark plugs are brand new. No recent work on anything intake related. Vacuum hoses are all in bad shape though. I'm thinking of doing a smoke test next. Any suggestions on how to do this?

SoCal911t— Nice catch haha. Ferrous metals wouldve made sense there (if I was possibly chasing a failed ims bearing). Let’s edit ** found tons of copper shrapnel and copper bits in the filter housing and sump and confirmed it was bits of rod bearing material. Mains were also not in great shape either.

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You Tube Hopefully this can help a bit

PROBLEM SOLVED. Hey guys, thanks for all your help! I found the issue to be a leaking intake tube during my smoke test. It's strange the a leaking intake would only cause misfires in bank 1. Apparently Porsche states that leaks in certain points can affect only bank 1 or bank 2. Solution: The leak ended up being on a tube connecting to my air oil separator. I ended up doing the smoke test to detect a leak, seeing a leak coming from somewhere in the driver's side rear engine. After removing my alternator and entire intake manifold I could see the cracked tube. It was here that I realized I could have accessed this tube from the bottom without removing anything (Dang I need a car lift . Anyway I attached a picture showing the leak and also a diagram to show the part that I need to replace. Also linked below is another thread with a very similar problem/fix https://www.renntech.org/topic/39522...r-engine-work/

Good Analysis! Congrats on the result and thanks for reporting back to the thread.

Congrats on finding that leak !!! That thing looks like it has been there for ages, now test the Crankcase Vent System with a Manometer to make sure the AOS is ok...