Engine vibration and misfire - can't figure out issue

[Steve L.]

My EVO Supercharged 2003 C2 Coupe with 6 speed started having problems about a month ago and it has been a nightmare trying to get this resolved. The engine is currently reporting a P0305 misfire on cylinder 5 code however in the past it has also reported P0304 misfire on cylinder 4 and only one time it reported P1371 - Valve life control, checksum error although this code has not returned. Sometimes the car operates normally other times I feel a slight to moderate vibration and then the check engine light starts blinking. The vibration only seems to occur when the engine is at idle or under minor load with no acceleration and usually low speeds or highway cruising. The repair shop has replaced all plugs, the Mass airflow sensor, and installed a new air filter. The say it is not loosing compression, they have checked and swapped the coils and spark plug wires to see if the problem happens on other cylinders and it is always on cylinder 4 and 5. Since we changed the mass airflow sensor it is only reporting cylinder 5. The repair shop does not feel the problem is the valves because the problem happens under low load on the engine.

Can any one offer any suggestions on where to go with this. Thanks for any help in advance.

[Scouser]

Steve,

I hate to say it, but guys over hear who have had cracked cylinder liners experience similar problems. The car seems to run fine except at idle or low revs where it shakes, missfires etc. But in their case, the cars overheated as a result of coolant vapour escaping into the combustion chamber via the crack (and nobody seems to know exctly how the crack appears). Does your car overheat?

But before I'd panic I would have them replace the HT & plug leads set, and replace the coil pack in the bad cylinder.

Not sure what the SC does in the way of electrics/timing etc but could it be that?

Anyway best of luck with it m8.

[geza]

Bad injector perhaps - any tests on these items?

[Ubermensch]

I'm not a huge fan of compression tests, when leak-down tests are much more informative. I'd suggest you have the shop perform the leakdown and this will help identify and defects in the block, rings, or valves.

Also, compare the plugs in the cylinder that reports a misfire and see if it's running lean or rich relative to the other cylinders.

Shawn

[nick49]

I hope I'm wrong but your description makes me think of coolant leaking into a cylinder. It would cause a misfire code, and with a small leak, the rough running would be most noticed at very low rpms. CEL will flash if it detects coolant in the combustion chamber or exhaust tract. These symtoms sound familiar with the slipped or cracked sleeve issue I just went thru with my '99. Knowing what I do about the M96 motor design and how failure is occuring often in areas of the cylinders and intermediate shafts, I would be afraid to stress one beyond normal aspiration. The TT and GT3 use a different design that yields itself to much higher loads and stresses found in competition. Good Luck

[Steve L.]

The car is not overheating at all. I have a feeling the problem is more appearant on a warm engine rather than a cold one but I am still trying to figure that out. Also I think the shop has done a leakdown test but I need to confirm. The terminology is slightly over my head when they are speaking to me. I know they have done a smoke test and something called a ozone test I believe. I will call them today and try and get my answers straight. They are trying to form a plan before we proceed.

One suggestion that had me spooked involved drilling a hole in the head and mesuring the hydrocarbons. That doesn't sound so great....

A few of you have mentioned various issues with the engine and expressed hope that this is not the problem. What is the recourse if this is the problem such as the cracked sleave or coolant leaking into the cylinder? Can this be fixed or is this a engine replacement issue?

[Scouser]

The car is not overheating at all. I have a feeling the problem is more appearant on a warm engine rather than a cold one but I am still trying to figure that out. Also I think the shop has done a leakdown test but I need to confirm. The terminology is slightly over my head when they are speaking to me. I know they have done a smoke test and something called a ozone test I believe. I will call them today and try and get my answers straight. They are trying to form a plan before we proceed.

One suggestion that had me spooked involved drilling a hole in the head and mesuring the hydrocarbons. That doesn't sound so great....

A few of you have mentioned various issues with the engine and expressed hope that this is not the problem. What is the recourse if this is the problem such as the cracked sleave or coolant leaking into the cylinder? Can this be fixed or is this a engine replacement issue?

Rebore and new cylinder liners. There's an excellent article on this in April's (last month) 911 & Porsche World mag. The magazine outlines a company in the UK called Autofarm who have a solution for this which essentially is an engine rebuild. But the mechanism of using silsleeve inserts is well known in the Motorsport part of the industry. You should take your car to a decent independent and they can tell you more about it.

Cost over here for a silsleev insert rebore is about £4000 therabouts. A full rebuild is double that.

I truly hope youcan get this sorted without need this recourse.

I do however agree and so do several very good independents here in the UK, that the NA 996 engine has too many problems to expect to get long term use with an SC fitted.

[Ubermensch]

One suggestion that had me spooked involved drilling a hole in the head and mesuring the hydrocarbons. That doesn't sound so great....

Hopefully you misunderstood and they want to drill and tap a hole in your exhaust to measure the A/F ratio on a wideband sensor to understand the mix ratio. I've never heard of drilling a hole in the head of an engine to measure fuel or exhaust gas ratios....

[bnewport]

I have a similar problem on my 99 996 tip. My problem is that at 6k+ RPMs at steady throttle then I get a CEL. The dealer ended up replacing the lifters and carriers and DME but the problem still occurs.

Two weeks ago my tip failed, they said a bearing on the front pump seized and then a seal blew. Fluid dripping all over the place. So, 10k for a new tip and I mentioned the misfires again. The mechanic think it may have been the tranny doing now.

The dealer and PCNA went over the engine last year but all they came up with was lifters and DME to no avail. The last suggestion before the tranny issue was an unbalanced drive shaft.