LS7: Injectors have 12v and signal pulse but 4 of 8 don't fire!!

Vehicle in question: 2008 Corvette Z06. Engine: LS7. ECM: E38

I'm trying to help a friend with the diagnosis on this one but i'm almost stumped. Cylinder heads were off for rebuild. Everything put back together but now it's only firing on 4 cylinders. The dead cylinders are 1,5,6,8. It has been narrowed down to injectors not firing. The injectors have their constant 12V power. When a noid light is connected they appear to get a correct pulse signal (has not been checked with a scope yet, will be checked with scope soon). Injectors have been swapped around, inactive injectors stay with the same cylinders. All harness connections have been verified. All harness grounds have been checked. The coils do fire and it does have spark. Fuel pressure is good.

What makes this interesting is the cylinders in question are on both banks. Also worth noting is the signal pins for these injectors on the ECM are all adjacent, which seems like it can't be a coincidence. It will be tested with a scope but thought i'd see if you guys have any thoughts. I'm suspicious of it being the ECM at fault since it does appear to provide the signal pulse. Maybe the signal is weak and not adequate to actually operate the injectors? I thought of possibly moving the pins on the ECM (obviously just for testing purposes with the rails off) just to confirm it is not an issue with the injector harness/connectors. Let me know what you think! This should be a fun one!

Being that it lights a noid light, my thought would be that the circuit is unable to carry a load.

Do tests while the injectors are plugged in. Backprobe the control wire of the injector and use a test light on battery positive and see if it pulses.

Was the car off the road for a prolonged period ????? as from your description it although you have swapped injectors sounds like stuck injectors. To be sure use a higher wattage test light as a Noid light. A 5 watt or even a 21 watt bulb should be okay as a realistic load First use it first as a straight Noid light, if no activity then check between the injector 12v power and and cylinder block ground. Then with lamp direct powered from battery +12v check the controlled ground wire is pulsing.

Gasoline has always had a shelf life it used to just become less volatile and form varnishes but modern fuels don't store well because of bio content and reduced sulfur they tend to gell and cause corrosion.

Do you have bi directional scanner to do an injector balance test?? I’d pulse them then do a voltage drop test on the feed. Maybe try grounding them manually see if they flow any fuel on the fuel pressure gauge

How did you determine that it is injector related if you have power and control and swapping the injectors didn't change the location of the misfires?

Not trying to be a naysayer, just wondering what evidence you have that the injectors are not firing on the problem cylinders.

So maybe not the most comprehensive evidence, but no fuel/fuel smell on the plugs and no noise of injector action when checked with a stethoscope. And fuel pressure, spark, and compression were all confirmed good - which led to an educated guess of injectors.

I would follow Cheryl's advice and perform a flow test next with a scan tool and fuel pressure gauge.

Update: pressure drop test confirmed injectors do fire. Compression test had been done before and was supposedly ok. Was checked again with another gauge and the dead cylinders all showed less than 70 psi and terrible leak down. Turns out the head rebuild involved a valve job that doesn't seal at all lol. Thanks for the pointers everyone! Hadn't used the pressure drop method before but it's a good one!