Why does cam change create misfire????
08-30-2005, 06:57 PM
#1
Why does cam change create misfire???? I have a cam and head swap in my LS1 69 Camaro. Having a tough time getting the TCC to stay enabled.
Had my buddy ride in it today with a tech II to monitor.
It is getting misfire across the board, but not enough to set a SES.
We relearned the crank sensor and it stayed in a while longer, then slipped out again.
I have read on here that cam swaps can create the problem. Why?
What all can be done about it?
Had my buddy ride in it today with a tech II to monitor.
It is getting misfire across the board, but not enough to set a SES.
We relearned the crank sensor and it stayed in a while longer, then slipped out again.
I have read on here that cam swaps can create the problem. Why?
What all can be done about it?
08-30-2005, 07:34 PM
#2
Originally Posted by 69MyWay
I have a cam and head swap in my LS1 69 Camaro. Having a tough time getting the TCC to stay enabled.
Had my buddy ride in it today with a tech II to monitor.
It is getting misfire across the board, but not enough to set a SES.
We relearned the crank sensor and it stayed in a while longer, then slipped out again.
I have read on here that cam swaps can create the problem. Why?
What all can be done about it?
Had my buddy ride in it today with a tech II to monitor.
It is getting misfire across the board, but not enough to set a SES.
We relearned the crank sensor and it stayed in a while longer, then slipped out again.
I have read on here that cam swaps can create the problem. Why?
What all can be done about it?
Bill
08-31-2005, 09:59 AM
#3
Cam swaps create a problem because the method of misfire determination that GM chose to use for the LSX is based off of the crank reluctor wheel. The misfire detection monitors an acceptable change in reluctor wheel speed with each ignition within the engine. If the reluctor wheel speed change with each ignition does not match what is anticipated by the PCM it is chalked up as a misfire.
The larger the cam that you place in the engine the longer the cam holds the intake valve open for. At lower engine rpms, where there is little to no inertial velocity of air into the cylinder, this hanging of the intake valve actually allows air to revert over the intake valve. This reversion causes inconsistant combustion within the cylinders. This inconsistant combustion within the cylinders at lower rpms sets off the misfire detection. Once the rpm of the motor is up enough to enact some form of inertial velocity for the inlet air, the reversion is greatly reduced and it is business as usual for the motor.
If the cam is large enough to set off the misfire detection you will have to have it tuned to either disable or dampen the misfire detection. Otherwise the PCM will always command the TCC to unlock in the event of a misfire. The only other option is a manual lockup switch.
The larger the cam that you place in the engine the longer the cam holds the intake valve open for. At lower engine rpms, where there is little to no inertial velocity of air into the cylinder, this hanging of the intake valve actually allows air to revert over the intake valve. This reversion causes inconsistant combustion within the cylinders. This inconsistant combustion within the cylinders at lower rpms sets off the misfire detection. Once the rpm of the motor is up enough to enact some form of inertial velocity for the inlet air, the reversion is greatly reduced and it is business as usual for the motor.
If the cam is large enough to set off the misfire detection you will have to have it tuned to either disable or dampen the misfire detection. Otherwise the PCM will always command the TCC to unlock in the event of a misfire. The only other option is a manual lockup switch.
08-31-2005, 10:05 AM
#4
NoGo,
Thank you for that great explanation. I understand better now. Working now on making sure my crank sensor is okay as my tuner is confident the misfire has been tuned to the point it should not be causing a problem.
Thanks a bunch!
Chris
Thank you for that great explanation. I understand better now. Working now on making sure my crank sensor is okay as my tuner is confident the misfire has been tuned to the point it should not be causing a problem.
Thanks a bunch!
Chris
