Changed the spark plugs today, BR7EF gapped at .034". The old ones looked fine. Fired it up with a fuel gauge on it, steady 50-55 psi. Still running just like before, very crappily. When I took header temps, the back 3 cylinders on the driver's side (3,5,7) and back 2 passenger side (6,8) were not firing.

I checked the main harness to the coils and did the individual wire tugs for a broken wire, they checked out. Did the tug test on the coil harnesses and injectors. I have an inline spark tester coming Tuesday so I can see if the plugs are getting power.

What would cause 5 cylinders to stop firing all at once? Is there a commonality between those 5 cylinders? Wire, fuse, anything?

 

Ignition power all coil powers run to a splice pack in harness for drivers side coils at one splice pack and antoher splice pack for the passenger side. Splice packs are like 6 to 8 inches into the harness from the branch point.

Start truck check for power on pink and black at the coils. Check coils easy way take a old spark plug ground it and crank motor see if you have fire.

Stick a noid light on the injectors and verify their operation also.

 

Do a crank relearn too. Might be the reluctor wheel or crank sensor is out of whack and changed the reluctor profile.

 

Getting spark per the spark light. Fuel pressure is fine. Checked the ohms of a couple of the non-firing cylinders' injectors and they matched the firing ones at about 12.6 ohms.

But here's the crazy part, when I listened with my stethoscope, the non firing cylinders' injectors sounded like they were clicking the same as the good cylinders. I'm guessing that indicates a blocked or clogged injector. But how would that happen to five injectors simultaneously (if that is the problem)?

Going to see if I can find a set of noid lights locally and test again to make sure.

Absolutely stumped and in need of advice.

 

Compression test?

 

Haven't tested compression yet

 

Update:

Gave up on it and towed it to Century Automotive in west Houston, who also built my trans. They found two broken valve springs. The sad thing is I've been meaning to replace the LS6 valve springs for a number of months now since they have 50-60k miles on them, but just kept putting it off. $700 later, I should be back on the road. Picking it up today or tomorrow after work.

But the good thing is that the valve springs didn't take out the engine. That is a weekend chore that I did not want on my to-do list.