9 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCH2001 C4 Misfire and stall, out of clue, help!!
Leading reported evidence
Replace entire crank sensor wire
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
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Performed · outcome unconfirmed · Original poster
After I replaced the entire crank sensor wire from end to end directly to the ECU, no random misfire for 4 months and 800 miles.
Leading evidence: 'Replace entire crank sensor wire' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check next would be much appreciated' (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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Suggestion · Original poster
Any suggestion on what to check next would be much appreciated.
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.
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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.
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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.
9 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: 20261026T225432Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
I purchased my C4 last year. Engine was rebuilt by Vertex at seller. I put around 4000 miles last year and lately has been experiencing random misfire (P0300). Various misfire around all cylinders. A couple episodes that the engine stall during cruising. I had to pull over to the side, and able to re-crank the engine. When it is not acting up, the engine runs strong and smooth all the way to redline no problem. Here is what I have done so far to diagnose the problem:
Vacuum leak check, smoke check--okay
Replace fuel pump, fuel filter, and pressure regulator
Check fuel pressure, and it meets specs at around 50 psi
Replace spark plug and ignition coil
No other error code other than P0300 and random P030#'s
I also unplug MAF to see if MAF is giving out weird signal, it still misfire randomly
There is no pattern that the random misfire only happens during cold or hot engine
Misfire happen mostly around 1800 to 2500 RPM.
I am not running out of clue. Any suggestion on what to check next would be much appreciated. Thanks.
No, as Vertex only rebuilt the engine, as the owner only shipped out the bare engine with no accessories attached. I am thinking, since the symtom affects both banks randomly, I am following thoughts of what is commonly sharing among all cylinders. Can the next thing be the crank position sensor?
Well, for starters anytime a code is set, there are "freeze frame" date that is collected at the same time. Tells the parameters at which the code was set ie, rpm, temp, fuel trim short and long, 02 sensors ect., at the exact time the code was set..This is invaluable if the code if not self evident.
Thanks. I am using Durametric. Maybe I missed it big time, but I could not find where I can retrieve freeze frame data....My DME is ME7.2...Do you know this ecu supports freeze frame.?
Fixed! Thought I would give an update for people with similar symptoms. The last thing I did a few months back was to rip out the entire engine harness and clean all the connectors, sockets, and stripped all the old dusty greasy wire wrapping and re-wrap them. But with all these effort, the main thing I noticed was that the crank sensor wire was a shielded wire when I accidentally stripped it with knife. The shielding must have been aged, feel kinda brittle when I tried to replace the stripped section. After I replaced the entire crank sensor wire from end to end directly to the ECU, no random misfire for 4 months and 800 miles. I called the culprit was this aging shield wire failed to isolate interference when the engine rpm was low, as the signal voltage was too weak even at 1800 to 2000 rpm to confuse the ecu. Hence, the misfire only happened at low rpm and not for high rpm ranges.
