high RPM misfires, but no codes

[Hurst Equipped]

deleted

[Hemi31]

Could be a timing issue.Remember Andrew was talking about the PCM learning the new cam position with the Starscan?

[Hemi31]

why no codes????????
I wish I knew.I hate computers!

[fnkychkn]

until the PCM learns the CAM/CRANK difference (adaptive numerator), it will not detect misfires. the adaptive numerator is lost whenever the PCM is powered down (batt disconnect/fuse 11).
from FSM:
The Adaptive Numerator must be learned before the PCM will run the Mis-Fire Monitor. The PCM updates the Adaptive Numerator at every key-ON, and is relearned after battery disconnect. The Misfire Monitor will not run until the Adaptive Numerator has updated since the last battery disconnect. If the Adaptive Numerator is equal to the default value then the PCM knows that the Adaptive Numerator has not been learned and does not permit the Misfire Monitor to run. If the Adaptive Numerator exceeds a calibrated percentage, the PCM sets a DTC for CKP NOT LEARNED and illuminates the MIL.

[fnkychkn]

the PCM will relearn adaptive numerator on it's own. it learns this during closed throttle decelleration when fuel is shut off so there is less chance of crank speed fluctuation.
if PCM is counting misfires, you can see which cylinder is misfiring.
ECU view > PCM > more options > monitors > OBD2 monitors > which cyl is misfiring.

[Redfox0099]

www.autotap.com (http://www.autotap.com)

[Jaak]

www.autoenginuity.com (http://www.autoenginuity.com) will do it as well. You can see the counts, see errors stored and clear them.

Hey Red, have you been using autotap? If so, how's it been working out?

[lafrad]

did it misfire with your last valvesprings?

Maybe the new valvesprings really aren't any betterthan the old ones on this cam profile?!?

[FloridaRT]

Had the same problem with my 61' Pontiac years ago, seems I had installed the timing chain wrong, I was 2 teeth off...................had just installed hot cam.....

Car ran great at low-mid speeds, at high rpm it would actually blow gas up and out of the carb.

Check cam timing?????????????????????????

Bob

[maneval69]

A screwed up Rev limiter?

[Jaak]

A screwed up Rev limiter?

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So far, I'd say that's a good diagnosis. Oh, sorry, you meant on the car!

[FloridaRT]

How many miles on spark plugs???????????????

Maybe just need new spark plugs??????????

Bob

[FloridaRT]

i'm hoping it's the plugs, but they only have 1200 miles on them.


Are those the stock plugs???????????

Or did you install some new ones??????????

Are they the right type???????????

Bob

[FloridaRT]

I would stick to the original type plugs...............cheaper also.

Bob

[VanillaRT4me]

It's just the rev limiter from what I understand.

Spark is simply cut to several cylinders to prevent going far past redline. This method has been used for years on high-performance motorcycles.