Hey all, so I've got a 07 suburban with a 5.3 with the unfortunate afm. It has a constant miss on cylinder 1 and 3 I've swapped coils, wires, new plugs etc and nothing changes. Checked compression on them and #1 is around 120-125 and # 3 is closer to 150. I'm getting fuel bc the plugs are doused in fuel, number one is also covered in oil... I hear this is normal for afm vehicles. I dont think im getting spark at them but its hard to tell bc its got some weird boots that do not fit a tester and I can't get the plugs to spark by holding them against the exhaust. Looking for insight in something I may have overlooked or anything really at this point. I need this truck so I really can't afford to have it sitting.
Thanks!

 

Check for power to the coils. You should have spark at the plugs holding them to the exhaust. Wet plugs mean they are not firing.

 

If you do have power to the coils, with a test light connected to the battery positive terminal place the pointed probe in the other wire connector of the coil that is not firing and crank the engine , the test light should blink everytime the PCM grounds the coil. If not , verify wiring from PCM is complete to the coils in question. If no fault found in wiring ,
Good chance , PCM has a problem.

 

I’ve checked power I’ve got 12v on supply, 12v on signal, and 1v on low reference on both. The only thing I can think is pcm isn’t cycling the signal on and off to actually fire the coil.

 

I would say it's the grounds on the front of the engine on that side but if it's only an issue with 1 and 3 and not 5 and 7 then I'm not sure what it could be.

 

I thought that too at first but all 8 coils ground at the same spot so if I still have 6 working fine I find it hard to justify being a contortionist to try and get at the ground being it’s blocked by the front diff. I have power at the coils they just aren’t being commanded on/off and I definitely have fuel the plugs are soaked.