2004 C4S Misfire on Cylinder 4

I have an issue with my 996 2004 C4S. The CEL came on a while ago and I took it in. The car has 110K miles (171K km) on it - well broken in :-) Anyways, I replaced the coils and plugs which is really needed - the coils looked terrible. The car still didn't run well. The code came back for a misfire on cylinder 4. Well, my cousin, a certified mechanic, did a compression test for me and found cylinder 4 is at about 155 compression compared to 195 for the 5 and 6 cylinder. There was a ticking from the car. However, I have not seen any big amounts of white smoke as some people have noticed in their cars. My cousin said it could either be - 1) Valve issue 2) Valve lifter issue However, the service guy said it could be that or the whole cylinder needs replacing. From my readings on here, it sounds like the valve lifters are a common issue. Anyone heard of a whole cylinder going? The car still can function when cold. Thanks for any advice, Doug GTA area

What you need is a leakdown test. It will show you where the compression is leaking to and then go from there. At 155 psi, that cylinder still should fire just fine.

There is more than a 10% fluctuation between the cylinder 4 and others which is why there are issues. A leakdown test - can it tell the difference between a valve or valve lifter or possible cylinder lining issue?

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You want to be sure the compression test was done right. What follows is based on that. (That the cylinder is misfiring is not necessarily due to a bad cylinder. Sure you replaced the coils/plugs but the injector could be bad. A lifter could be bad too. That the noise is not present when the engine is cold and then when it is hot has my vote for a lifter but that's just my WAG and not a suggestion as to what to do next.) Anyhow, a leak down test can help id what's going on. Ideally the exhaust and intake manifolds want to be removed. The cylinder is pumped up and a listen is made at the exhaust ports and intake ports listening for the sounds of an air leak. A listen at the oil filler tube cap is done to see if the air in the cylinder is leaking past the rings/piston. What you hear or do not hear determines what comes next.

If the compression test is done with the throttle plate closed cylinder #4 will always be the lowest. This is due to the dynamics found inside the intake system at low speeds and how they impact chamber filling. The only way I find issues with cylinders on these engines with a compression tester is by carrying out dynamic compression tests. Also, leakdown tests are difficult to do as the crank must be held in 3 different positions to achieve readings from not only TDC, but also BDC and at "mid stroke". This means a special device to lock the crank is various positions must be created, and also requires camshaft manipulation to ensure that valves are absolutely closed during the tests. These are just some of the dynamics that make these engines less like Porsches and more like their own breed. You have to work with them specifically all day long, make mistakes and learn the hard way. Some people never figure it out. Yes, complete cylinders can fail, we see it all the time and routinely at 1/2 the mileage that your engine has.

This is getting depressing. Instead of an IMSB failure thread we need a M96-01/04, M96-03 failure thread.

Just wondering whether OP ever resolved this issue. My 04 C4S has been at a reputable indy shop since Friday morning with similar symptoms. The CEL went off as I was driving to work and I took it straight to Gtek. The initial diagnosis showed a misfire on cylinders 2 and 4. Jack recommended I replace all my spark plugs and ignition coils, which I agreed to. Later on Friday, Jack informed me that cylinder 4 was still misfiring despite the new coil packs and plugs. Today, Jack informed me that cylinder 4 showed lower pressures comparatively to the others but the leak-down test indicated that everything was fine. He is now in the process of swapping over an injector to determine whether the injector needs to be replaced. Failing that, Jack said that the lifter would probably have to be replaced and that this would be a massive job. I really really hope that its just a case of a faulty injector but want to be prepared for the cost of a valve lifter. Any idea as to how much such a job would run?

What were the leakdown and compression numbers? If the leakdown numbers are good then the cylinder is sealing well so I'm not sure why he would still think a vlave lifter could be the problem. Also, a fuel injector (unless stuck wide open) will have little or no effect on compression numbers. The leakdown test numbers are more important than the compression ones. Has he tries moving around the new plugs and coils to see if the misfire moves with them?

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You must've had nothing but leased honda civics before that black 4s. Literally every single car I've owned would have these kinds of posts showing up on the respective forums - new user with 1 post asking about VANOS codes on his M3, oil consumption/scored cylinders on his S4, torquer converter codes on his RS6/CLK55, worn valve guides on his Ducati etc. etc. Read: http://en.wikipedia.org/wiki/Sampling_bias

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Thanks for your response. I just followed up with the mechanic and he confirmed the following: Leak-down test result was 4%. Compression test on the cylinder was 80-100 while good cylinders were 155-165. He swapped around the coils and plugs to no avail. He now recommends that I change 2 intake and 2 outlet valves on the cylinder, which will cost $1500... sigh

Uhmmm 4% is still pretty good but the comoression number is low. Can he hear what port the air is escaping? To only have 80-100psi, the leakdown number should be double didgits. Something doesn't add up here. Chances are good that thr exhaust valves are leaking as they can get carbonned up but that means the other cylinders are not thag far behind. More testing needs to be done before declaring a complete valve change to that cylinder. It's unussual for all 4 valves to leak. I don't understand how can a 4% leakdown result in only 80-100psi.

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Maybe that's why Jake said the leak down needs to be done in 3 positions.

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Compression test numbers are low, provided the compression test was done correctly. This is very important to state the obvious. A lot is riding on this test. Not sure what 4% leak down test means. This test needs to be done correctly, too, and for the same reason as the compression test. If the compression/leak down test results are correct then there is a leak in the cylinder. Absent signs of a head gasket leak, a cylinder failure, intake/exhaust valves have to be the #1 suspects. Often all 4 valves are replaced. It is sometimes hard to tell which one is leaking. One may look bad and be bad while the other valves look ok but the cost of the extra valves is small compared to having to do this work again. My WAG is a valve is burned -- unless you cop to a money shift -- but the tech will know soon enough if you give him the go ahead to do the work.

If you don't know what the leakdown number mens then why are you giving suggestions on it? A proper leakdowm test will tell you a heck of a lot more than a compression test. My oppinion is that in this case the leakdown and the compression numbers are working against each other.

After some more thinking, I think the issue ia air not getting into that cylinder. That would explain the good leakdown but low compreasion. Either the one or both intake valves are not openning enoug or something is blocking the intake port for that cylinder. A collapsed hydraulic lifter or a severy worn camshaft lobe can do this but in any case, there isn't enough air going into #4.

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Thanks so much for your insight into the matter. Do you have a ballpark as to how much time such a job normally costs (replacing the 2 intake and 2 exhaust valves on cylinder 4)?

I do all my repairs and have no idea what they would charge. There will be lots of labour that's for sure.

Depends if they can get at all the valves without dropping the engine. They usually recommend doing all the valves on the bank but I figure you could do one at a time. Though if other ones acts up later you've wasted a lot of hours and money.

They looked at the other cylinders and said that the they seemed to be fine judging by the compression/ leak tests so I really hope this problem does resurface in another bay... Thanks all. If everything goes as planned, Gtek said that I'll have my car back Friday evening. Will report back with results and final bill tally. Cheers.

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My concern was for the reporting of the results. Sometimes numbers get bandied about and jumbled up. There is the issue of what pressure was used for the leak down test. I was taught to use 100psi but that doesn't mean every body does. I agree the leak down test tells one more about what's going on than a compression test, provided of course the leak down test is done correctly and full advantage of the test is taken.

The head has to come off. I'm not sure if this is an engine out job on the 996 or not. I've seen a head removed with the engine still in the Boxster Since I have never had to have an engine dropped in either of my cars I can't offer any real idea of the cost. Had a tranny dropped from my Turbo the other day to replace a RMS. Cost came to just under $1700. If all the cost was labor that was a bit over 10 hours labor at $150/hour.

Wow Friday evening, now that's fast. I take it the engine will stay in the car then? Last year when I was doing the top end refresh, it looked like there would be enough room to pull a head while the engine stayed in the car. Hopefully not many suprises or while you are at it stuff comes up during the work. Good luck.