Crank sensor cutting out intermittently w/random misfire
08-03-2019, 05:27 PM
#1
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Crank sensor cutting out intermittently w/random misfire So, one step forward, two steps back trying to get my 3.8 to 5.7 swap running completely. Hoping someone has some insight that I haven’t thought about...
‘99 trans am
EGR/AIR/Rear O2 deleted
LT headers/LS6 intake
Has random misfires at idle (cylinders 4&7). These misfires are based on my 1999 tune file firing order of 31872654. When I change to the 2000 tune file order of 18726543, the misfires move to cylinders 5&8. That kinda tells me maybe something tune related, not sure. However.....
When the engine is cold, I can rev it as high as I want to go, no issues (in park in the driveway). As soon as it gets up to temp, things change. Once at temp, when I rev it, it starts really shaking, revving rough, kinda chugging and won’t go higher than about 3.5-4K on the tach. Once it hits about that range, the tach dies, and it throws DTC P0336 for the crank position sensor. If I go in and clear the code, the tach instantly starts working again, unless I rev it again, then it repeats the same issues again.
I’ve swapped cranked sensors, ECUs, engine harnesses and no change whatsoever. Wondering is anyone knows of anything else that could cause it to change so drastically once it reached operating temp (except for vacuum leaks, already checked for those). What would cause the crank sensor to cut out at temp, killing the tach, but works again once code deleted....really getting frustrated with it.
Input I've received from other sites is either knock sensors or CASE relearn, and I can't do CASE relearn until I fix the rev limiting/crank sensor cutting out.
Thanks for any/all help!
‘99 trans am
EGR/AIR/Rear O2 deleted
LT headers/LS6 intake
Has random misfires at idle (cylinders 4&7). These misfires are based on my 1999 tune file firing order of 31872654. When I change to the 2000 tune file order of 18726543, the misfires move to cylinders 5&8. That kinda tells me maybe something tune related, not sure. However.....
When the engine is cold, I can rev it as high as I want to go, no issues (in park in the driveway). As soon as it gets up to temp, things change. Once at temp, when I rev it, it starts really shaking, revving rough, kinda chugging and won’t go higher than about 3.5-4K on the tach. Once it hits about that range, the tach dies, and it throws DTC P0336 for the crank position sensor. If I go in and clear the code, the tach instantly starts working again, unless I rev it again, then it repeats the same issues again.
I’ve swapped cranked sensors, ECUs, engine harnesses and no change whatsoever. Wondering is anyone knows of anything else that could cause it to change so drastically once it reached operating temp (except for vacuum leaks, already checked for those). What would cause the crank sensor to cut out at temp, killing the tach, but works again once code deleted....really getting frustrated with it.
Input I've received from other sites is either knock sensors or CASE relearn, and I can't do CASE relearn until I fix the rev limiting/crank sensor cutting out.
Thanks for any/all help!
08-04-2019, 11:33 AM
#3
TECH Senior Member
Give it more time. You only posted yesterday afternoon....
08-08-2019, 11:04 AM
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10-06-2019, 08:50 PM
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Bringing this one back for (hopefully) more insight. Car runs mostly fine when cold, but still garbage when warmed up. I've checked knock sensors, and crank end play, both are good. Swapped out O2 sensors. I've hooked an Oscope up to both cam and crank sensors, and both show good readings at all times, hot/cold, idle or revving. When it's warm, it starts bucking and misfiring, cam and crank sensor readings (in VCM Scanner) start intermittently going to zero, tach dies (until I reset the DTC), but The sensors are still actually sensing signals to the ECU. Completely stumped at this point, and seem to need help focusing here before I grenade everything and go Holley EFI...... Thanks y'all.