Cylinders 1 and 7 misfiring.

[Emilio4980]

I have a 08 GMC Sierra 1500 4 wheel drive with a 5.3 l in it . The problem I'm having is on the startup the vehicle seems to idle fine till it warms up then starts going to a cylinder one and seven misfire I have checked the noide on both injectors and that is fine I also did a compression test which was on cylinder one 125 psi and cylinder seven has 140 PSI. Also check the lifters and everything seems to be moving fine don't know what else to check.

Edited June 6, 2023 by Emilio4980
Misspelled

[dna9656]

Could be your ignition coil is warming up and an open is created by the expansion of the wire in the coil windings or wires supplying current to the coils, same could be true of spark plug wires.

[swathdiver]

21 hours ago, Emilio4980 said:

I have a 08 GMC Sierra 1500 4 wheel drive with a 5.3 l in it . The problem I'm having is on the startup the vehicle seems to idle fine till it warms up then starts going to a cylinder one and seven misfire I have checked the noide on both injectors and that is fine I also did a compression test which was on cylinder one 125 psi and cylinder seven has 140 PSI. Also check the lifters and everything seems to be moving fine don't know what else to check.

 

It is time to rebuild or remove AFM from your engine.  You have partially collapsed lifters or some other AFM issue.  It is SOP to replace the lifter trays (GM OE ONLY) when replacing a lifter and it is SOP to replace the VLOM when doing an AFM repair as it is the solenoids that usually get out of time and damage the lifters.  Solenoids get out of time due to extreme age and dirty old oil.

 

Use GM OE parts only, really inexpensive aftermarket parts won't get you down the block.  Do the repair right.  

[richard wysong]

listen to the injectors with a stethoscope or a long screwdriver held to your ear, they should make a distinctive "click" each time they fire. There are updated injectors for it as well

[Emilio4980]

I've checked the injectors they are both working. I've also swapped them to other cylinders to see if the problem followed the injector and no it didn't. Still have it misfires owners one and seven.

 

[newdude]

Sounds like an AFM or camshaft issue going on. 

 

I'm wondering if the VLOM solenoids are weak/leaking on 1 and 7 and are sending oil to those two cylinders and is either collapsing or trying to collapse the lifters on those two cylinders and its doing it when the oil gets warmed up and the pressure settles down. 

 

When you checked the compression, did you do it hot or cold?  Have you tried a running compression test once warmed up?  I'd check 1 and 7 and then the cylinders next to those so 3 and 5.  

 

Running compression test - AutoEdu - Testing procedure