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YOUR RESEARCH2004 C4S 3.6 - 50% leak-down at TDC, great compression leak-down at mid-stroke.
Leading reported evidence
Replace four lifters in
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No successful repair reported for this finding.
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Suggestion
I would replace all four lifters in that cylinder.
2004 C4S 3.6 - 50% leak-down at TDC, great compression leak-down at mid-stroke.
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Leading evidence: 'Replace four lifters in' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Replace four lifters in' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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2004 C4S 3.6 - 50% leak-down at TDC, great compression leak-down at mid-stroke.
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Interesting situation and hopefully can get some guidance.
Lumpy idle but ran fine once given gas. Pulled plugs and Cylinder 1 was toast while all others healthy. No misfire codes.
Did a leak-down test. All cylinders at 95/100 at TDC except for Cylinder 1 which is at 50/100. If I turn the crank (not sure of the actual degree), I can get 95/100, just not at TDC.
With the headers removed, it�s very apparent that it�s leaking from one of the exhaust valves. If I wiggle the valve, the sound of the air changes.
From my research it sounds like it might be a broken spring or bad lifter. Does that sound likely to you? There are no signs of valve contact on the piston when scoping, so I don�t think it would be a bent valve.
I�m planning on removing the cams this weekend to see if anything sticks out as broken.
On a track day back in 2005 with my dad�s old 2003 Boxster I accidentally over-revved and did something to wear a cam lobe and he had to have the cam replaced - problem is he kept quiet about it and didn�t tell me until years later so I wouldn�t feel bad. He�s dead now so I can�t ask him if he recalls the symptoms. That said, I�ve never over-revved this car as far as I can recall.
Would that not translate into a bent valve? If your reading is 50 at TDC but you turn it over another few degrees and you get a full 95 would tell me (at least thats what I thinking) it's bent. Is the plug wet or oily?
A bent valve will never close properly, no matter what position of the cam.
I think a broken valve spring or a hydraulic lifter that is somehow stuck, could well be the cause here.
If you can believe it I've seen slightly bent valve stems close and seal after the stem is pushed back down into the valve seat on motorcycles. I had one on my Ducati and it still ran.
There is a video that Jake did on the lifters. He says they basically fail very infrequently, but when they do, they can fail stuck in the extended position. I know the lifters on the .2's are very different from the .1's. If this is all DIY, this should be pretty cheap to do, but a lot of work. Congrats! Once you do get a new lifter, you can always do the leakdown and compression checks with the engine out of the car.
I know I have the video saved, but it's not titled lifter, but it's a Renvision video. Can't easily find it right now.
I would replace all four lifters in that cylinder.
I was somehow under the impression that in a normally running engine, the hydraulic lifters would be full of oil (check valve would keep the oil in) and they would then be hard to compress. Failing lifters would not hold oil pressure and would be ... springy. But ... what do I know?
