Looking for some fresh eyes on a high-RPM misfire I’ve been chasing on my
2006 Cayman S
.
The car has a Flat 6 Innovations / Jake Raby Stage I Street Performer 3.6L and currently has about 69k miles...engine build about 20K.
The problem was already present when I bought the car. At that time it still had the factory dual-mass flywheel, and I have pictures showing stored misfire codes for cylinders 1 and 4.
The basic symptom is that under heavy load at high RPM, generally around 6k+, the CEL starts flashing. The strange part is that there is no noticeable hesitation, stutter, breakup, or obvious loss of power when it happens. From the driver's seat, the engine continues pulling smoothly. If the CEL weren't flashing, I wouldn't necessarily know the
DME
was detecting a misfire.
Depending on the pull, the CEL may stop flashing by itself, stay illuminated afterward, or the
DME
may shut down cylinder 1 until I cycle the ignition. Obviously, once the
DME
actually disabled cylinder 1, that was noticeable.
I can also free-rev the engine to high RPM in neutral without triggering the problem. It only happens under load.
A few weeks ago I had the clutch replaced. At the same time, the DMF was replaced with a lightweight flywheel (Sorry Jake), all six
spark plugs
were replaced, and all six coils were replaced with new BERUs. The high-RPM issue remained afterward. Since the plugs, coils, and flywheel were all changed simultaneously, I can't really separate what effect any individual change may have had. The important part is that the problem definitely existed beforehand with the DMF and old plugs/coils.
Things I've done/tested since:
Swapped the new #1 Bosch plug for a new NGK as another test. No change.
The crankshaft position sensor had a surprising amount of metallic debris stuck to the tip. Replaced the CPS, no change.
Performed a battery/DME reset followed by several in-gear overrun cycles. No improvement.
Logged actual vs commanded lambda on both banks. I didn't see an obvious lean event corresponding with the CEL.
Logged ignition timing and didn't see an obvious global timing event corresponding with it either.
Foxwell misfire/roughness data shows activity on multiple cylinders and both banks, but cylinders 1 and 4 have consistently been the standouts. On one pull, peak misfire counters were roughly 67 on #1 and 78 on #4.
Found a some oil getting into the intake through the AOS system. Replaced the AOS and cleaned up the oil I could access. No change to the high-RPM issue.
I previously had an IPD Competition plenum and 82mm GT3 throttle body installed. Interestingly, with the larger intake setup the CEL/misfire detection occurred at a lower RPM. Going back to the stock plenum and throttle body moved the onset higher, but didn't eliminate it.
I also have the original FSI build sheet. The engine received new timing chains/guides/tensioners, new OEM valve springs, exhaust lifters and other associated components. The sheet specifically notes that the VarioCam Plus intake lifters were not replaced as part of the standard build.
The combination I'm having trouble making sense of is:
High-RPM/load-dependent misfire detection, cylinders 1 and 4 showing the most activity, no noticeable stumble or hesitation while it's occurring, clean free-revving to high RPM, and the onset RPM changing with increased intake airflow.
Curious if anyone has encountered something similar on an M97, particularly something that showed significant misfire counts without the engine actually feeling like it was misfiring.
Any experience or ideas would be appreciated.
Try turning on logging.. and log the following:
Camshaft angle requested
Camshaft angle actual
That will tell you immediately if the cam adjusters are an issue.
- Measure fuel trim, short-term and immediate, requested vs actual..
That will give us a clue if the injectors are an issue..
