28 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHLeak down test fail
Leading reported evidence
Replace plugs and coil packs
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
Based on review of threads here, I replaced the plugs and coil packs.
Leading evidence: 'Replace plugs and coil packs' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'cylinder' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Replace coil pack and plug' (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.
Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed
Heck, I use a lab scope with an inductive pick up on the positive battery cable to perform a compression evaluation too..
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that suspect a cause
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suspected cause
If the vacuum guage shows rapid oscillation then do a running compression test.The cranking compression test tells what the engine is capable of .The running test shows what it actually is.Just put the compression tester in and start the car let it idle and record your findings.There shouldn't be much variation from the other cylinders.If your running compression is low on three cylinders compared to the other three you most likely have a valve timing concern.If its low on the suspect cylinder then you have a valve train concern.Could be sticky valve,lifter ,etc.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
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Suggestion · Original poster
After changing the coil pack and plug, it persisted.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
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Suggestion
Use the same comp tester the next time, as they are notoriously inaccurate, but you are looking for a change, not an absolute value.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
If the vacuum guage shows rapid oscillation then do a running compression test.The cranking compression test tells what the engine is capable of .The running test shows what it actually is.Just put the compression tester in and start the car let it idle and record your findings.There shouldn't be much variation from the other cylinders.If your running compression is low on three cylinders compared to the other three you most likely have a valve timing concern.If its low on the suspect cylinder then you have a valve train concern.Could be sticky valve,lifter ,etc.
These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
cylinder
No successful repair reported for this finding.
0
Identified cause
1
Suspected cause
0
Reported fixes
Read evidence and context
Discussions that suspect a cause
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suspected cause
If the vacuum guage shows rapid oscillation then do a running compression test.The cranking compression test tells what the engine is capable of .The running test shows what it actually is.Just put the compression tester in and start the car let it idle and record your findings.There shouldn't be much variation from the other cylinders.If your running compression is low on three cylinders compared to the other three you most likely have a valve timing concern.If its low on the suspect cylinder then you have a valve train concern.Could be sticky valve,lifter ,etc.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
28 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261027T005001Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
So I did the unrthinkable and bought a 2003 c4 cab in February without a service history. What can I say, the price was right. It had passed a trusted local PPI (somewhat limited in nature). They added a 3 year 3rd party power train warranty for a reasonable cost.
In the first few weeks, it started to throw a 3rd cylinder misfire code fairly routinely. Based on review of threads here, I replaced the plugs and coil packs. I took care of some easy consumables (no service history) and it has been running great since then. Runs smooth, pulls strong, and no codes. It doesn't blow any unusual smoke either.
Fast forward to this past week. I noticed a blister on one of my rear tires. The best deal on PS2s was at the Porsche dealership. On a whim, I asked if the car had been serviced there. Turns out, the PO used them for all service over the past decade or so. Had some good surprises like AOS, water pump, etc. last year, he started getting some misfires in cylinder 3. After changing the coil pack and plug, it persisted. They finally did a compression test (passed) and leak down test (87% cylinder 3!). At this point, he refused further investigation and presumably traded it in to another dealer.
Again, it runs great now and has so for the past several months. Would anyone pursue further diagnosis on this? I have convinced myself that a stuck valve has burned off whatever carbon may have been on it through aggressive driving.
No worries as long as you don't have any pending or active codes anymore. The DME is watching every single ignition for you so you can count on it.
If cyl #3 is leaking 87% now, your engine should run like crap
If you want to know for sure, test it yourself.
I have never met a technician as thorough or competent as I want them to be... Speaking as a former tech, and currently responsible for my company's warranty program.
Sadly the pinhead that did the leakdown test (it's actually a differential pressure test with orifice) didn't report where the leak was going. Grrrrrrr. This is not rocket surgery. Listen to the exhaust, intake, or oil fill cap when doing the test and the sound of the air escaping in this amount will be easy to determine. Exhaust valve, intake valve, rings.
Yep, not noting whether the leakage was past the rings (into crankcase) the exhaust valve, or intake valve was very amateur. Here we only use a leak down test to know WHERE the leakage is coming from, because when we perform one, we already know that we have an issue with compression.
That said, if the issue existed then, and not now, the engine probably had a lifter that was stuck, not allowing one of the valves to seal. We see this happen from time to time and it can clear it's self up. Thats about the only thing that would net an 87% loss of cylinder charge and not still be a problem (or even bigger problem) today.
I'll call on Monday to see if anyone has more detail. This was a year ago, so if it is not on the computerized record, I doubt it exists. I think I'm hearing encouraging things from you guys though.
Grab up a cheap comp tester at Orielly's and do all six at normal temp. don't squirt anything in the jugs before taking the test, and hold the throttle all the way open when testing. This will get you a nice baseline which includes the adiabatic effect on the ring expansion. Mark the numbers down in your mx log, and if it comes up again, you have something to compare to. Use the same comp tester the next time, as they are notoriously inaccurate, but you are looking for a change, not an absolute value. i.e baseline is 166, 162, 170, 158, 167, 166, then if you come up with a test later, you can compare to pre-existing values. If it shows something different, proceed to the differential test(leakdown), and find out where the air is going.
Pull the fuel pump/ DME relay and turn the engine over while filing it on the starter... Post about 8-10 seconds of the engine just spinning over without trying to fire up.
I'll tell you if you have low compression or not.
Teek: I would do as Jake says. He has a "calibrated" ear! Pretty scary, but I guess years upon years of hearing then tearing apart plus understanding how everything works inside makes one hear things us regular guys miss!
Heck, I use a lab scope with an inductive pick up on the positive battery cable to perform a compression evaluation too.. It works much like my calibrated ear.
I perform a "compression test" on every car, every time I start it.. Comes from years of driving aircooled VWs more than anything else.
If the car missfire is happening when cold ,put a vacuum guage on manifold vacuum port have someone start the car watch the vacuum guage if it pulsates rapidly then you have a problem internally,it should be stable. If the vacuum guage shows rapid oscillation then do a running compression test.The cranking compression test tells what the engine is capable of .The running test shows what it actually is.Just put the compression tester in and start the car let it idle and record your findings.There shouldn't be much variation from the other cylinders.If your running compression is low on three cylinders compared to the other three you most likely have a valve timing concern.If its low on the suspect cylinder then you have a valve train concern.Could be sticky valve,lifter ,etc.
So, the car is in for a clutch and IMS bearing. I thought it would be a good time to tear into what is causing the CEL that still occurred in cold weather (I did buy a warranty with the car).
Turns out it was a broken valve spring.
Really? CONGRATULATIONS !! Glad you got it sorted and never suffered any collateral damage (like a dropped valve) that could have happened with a broken valve spring !! Now quickly go buy a lottery ticket !! lol
