Code P0300, All Cylinders only in P or N?

Tiny
CDOROCKI
  • MEMBER
  • 2021 JEEP GRAND CHEROKEE
  • 6.2L
  • V8
  • 4WD
  • AUTOMATIC
  • 5,500 MILES
I'm getting a rough idle accompanied with a P0300 code. Jeep drives fine but obviously want to resolve the issue and not risk long term damage.

My rig: 2021 Trackhawk, ordered June of '21 and took delivery in September. Currently at 5,478 miles. Modifications include a GT Haus cat back exhaust (installed at ~1500 miles), Legmaker intake (installed at ~2500 miles, Billet Technology catch can (installed ~50 miles), and Ravelco anti theft unit (installed at ~150 miles). PCM is unmodified on the stock tune. Always fueled with 93 at a Sunoco or other top tier station, and always watch them press the button due to some mild OCD and paranoia.

The vehicle has been at the dealer approximately 10 weeks and we were able to isolate the issue down to only misfiring when no load is applied and when transmission is in P or N. While driving under normal and aggressive conditions, no misfire is detected. Dealer has noted that all 8 cylinders will misfire, but not at the same time and will switch from bank to bank. Several tests have been conducted including vacuum and leak down tests, cam to crank timing differences, fuel trim/pressure/etc. All tests are coming back normal and within tolerance. Next step is likely to begin investigation into the motor and cam phaser to ensure no mechanical damage.

Thanks in advance!
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Thursday, August 4th, 2022 AT 8:04 AM

4 Replies

Tiny
CDOROCKI
  • MEMBER
Also, I wanted to add in the catch can, intake and exhaust have all been removed. Vehicle is back to stock form with the exception of the Ravelco killswitch - Which operates as a binary switch. Without the plug installed - the vehicle will not start. With the plug installed, the circuits are complete and vehicle starts as normal.
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Thursday, August 4th, 2022 AT 10:27 AM
Tiny
KEN L
  • ADMIN
Is this engine supercharged? Also have they updated the PCM or checked to see if there are any? The rough idle is telling me you may have a leaky intake valve which will affect the cylinders at different times. I would have them do a leak down test to see what comes up. When they pull the spark plugs do they see one that is colored different from the remaining plugs? I am very interested to see what's going on with this engine.
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Thursday, August 4th, 2022 AT 7:50 PM
Tiny
CDOROCKI
  • MEMBER
Hi Ken, yes, it is supercharged. PCM software had been updated to the most recent version. Also, leak down tests performed showed no sign of leak. From what I was told - none of the plugs look "Clean".
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Thursday, August 4th, 2022 AT 8:12 PM
Tiny
KEN L
  • ADMIN
I would try a new MAP sensor it must be off a little. Here are the locations of the sensors in the diagrams below. Check out the diagrams (below). Please let us know what happens.
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Friday, August 5th, 2022 AT 5:57 PM

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