1999 Chvey 3500 Truck 5.7

royg · April 28, 2007

I have a missfire on 2 and 7. It is not a real bad miss and the plugs is not fouled. It is only at idle. Scoped the ignition side and all firing good, no bad trace. No 300 codes set. Scoped the injector circuit at the pcm and 2 and 7 injectors are opening at the same time.

replaced pcm but still the same. Checked circuit for resistance and continuity and no wires on the ground side are shorted together. The hot sides are spliced toghther normally. Took compression test and all are good at 175psi. Checked valve springs and are ok. Rockers are moving like the rest. Replaced CKP and the connector. Scoped the CKP and trace has some holes. ALso replaced the Sequential port fuel injection with the revised Multi port. The kit came with all the coils. Replaced cam sensor and a lt of ignition stuff too much to list, plugs cap ect... The injector is not dead but just firing at the wring time. I changed alot of stuff that i didn't need to but this is kicking my but so i just changed it anyways thinking i might have overloked somerthing.

I'm thinking bad reluctor wheel but never seen one go bad. Can a bad wheel cause the pcm to fire 2 injectors at the same time?

This is a 1999 chevy 3500 truck, 5.7 engine.

TBLAZER · April 29, 2007

I have a missfire on 2 and 7. It is not a real bad miss and the plugs is not fouled. It is only at idle. Scoped the ignition side and all firing good, no bad trace. No 300 codes set. Scoped the injector circuit at the pcm and 2 and 7 injectors are opening at the same time.
replaced pcm but still the same. Checked circuit for resistance and continuity and no wires on the ground side are shorted together. The hot sides are spliced toghther normally. Took compression test and all are good at 175psi. Checked valve springs and are ok. Rockers are moving like the rest. Replaced CKP and the connector. Scoped the CKP and trace has some holes. ALso replaced the Sequential port fuel injection with the revised Multi port. The kit came with all the coils. Replaced cam sensor and a lt of ignition stuff too much to list, plugs cap ect... The injector is not dead but just firing at the wring time. I changed alot of stuff that i didn't need to but this is kicking my but so i just changed it anyways thinking i might have overloked somerthing.

I'm thinking bad reluctor wheel but never seen one go bad. Can a bad wheel cause the pcm to fire 2 injectors at the same time?

This is a 1999 chevy 3500 truck, 5.7 engine.

Have you checked the EGR system or for Vacuum leaks?

The EGR valve can be partially open by a piece of carbon stuck in it,this will cause a small amount of exhaust gasses to enter the intake system and cause an idle missfire.

A small vacuum leak will also cause an idle misfire.

How about the distributor cap?,#2 is fired right after #7,a crack in the cap will crossfire between this 2 missfired cylinders.I see the scope is not showing a problem with the ignition but you got nothing to lose by looking at it,check for oil leaking into the cap through the distributor.