Blown496

Long story. My 08 LS3 is procharger alky control 1000cc injectors. I bought it built this way. I have had no issues with it since I bought it in 2021. I do pamper it and don’t hammer much. It has a lumpy cam idling at 900 with about 15” vacuum. Last road trip was about 50 miles running low rpm in 6th. Yesterday I took it for a spin and about five miles on the road it started missing like it was on 7 cylinders. Idled fine but under load was not good. It jerked all the way home. No codes, no misfires. I pulled all the AC LS9 plugs and really saw no evidence of fouling.im guessing they were from 2013 when American Modern Performance modified the car. That was 10,000 miles ago. Maybe iridium plugs are different to read. I put in a new set NGK tr7ix 3690 plugs and it ran on all eight but was still a tiny little jerky like a vacuum leak. It was down on power so I hit the freeway and drove at above 2500 rpm and hammered it several times and it finally seems back to normal. Injectors likely but I’m old school carb guy so looking for advice. Pour in injectors cleaner? Hammer it more often? Fluke?

rykerwolf

I don't really have an answer for you other than possibly the plugs. Just wanted to add that this weekend me and a friend went out for some races and the exact same thing happened to his zo6 during a pull. His air intake did pop off, and we thought it may have fouled a plug so we changed the plugs. They all looked good, but we replaced them anyways. The problem was still there but definitely not as pronounced as at first. It went from a dropped cylinder to a little stuttering. Did a couple hits and everything seems great again. We also replaced wires just incase but they all looked to be in great condition when they came out.

If you ever figure this out, I'd definitely be interested to see. Sadly he wasn't logging during the run and all logs look the same now as before the issue occurred. Fluke maybe? No clue.

Kingtal0n

Aux injection system may be spraying or leaking into a region too far from the engine forming pools of liquid in the manifold or plumbing leading to distribution issues and cylinder wetting down putting out fire somewhere

Aux systems have been indicted for this behavior and hydrolocking an engine unexpectedly

Aux systems require periodic maintenance, filters, refilling, the pump is a wear item it needs to be changed every so many hours of use. It will fail eventually the filter will clog a line will leak etc... it needs constant attention or the engine could fail if tuned to be dependent on methanol or water aux injecting.

Blown496

I put on new pump last year and spent time on the phone with alky control going over the upgrades. The only thing I can see that may have been an issue is number one plug wire. It was up against the alternator. Not sure if it was arcing that caused a dark spot or just the dirt accumulation on the aluminum. They are MSD wires. I put a piece of fuel line around the wire to keep it from touching. I haven’t buzzed the engine more than a few times in short bursts in 2nd and third before this event. It’s 735 wheel hp so it gets loose easily. I drive it very little and baby it when I do. Might be the problem. I hit it pretty good several times after the plug change and it seems to run better each time. I will add that the dual nozzles are right in front of the maf sensor. This car has no cats no egr etc.

1Hotrodz

I would change out the #1 plug wire it's toast.

Blown496

so the plug wires all test good. Short term trim and ox sensors all in range . Long term 14 both banks. Vacuum 14 idle 20 at cruise. Running rom up to 2200 sitting the rom fluctuations are there but vacuum is solid. Sprayed water on the plugs, injectors and manifold with no change. I’m thinking I may send injectors to get serviced.

1Hotrodz

So how did you check the plug wires? For continuity? Or Mega-ohm resistance test (Meggar-Ohm)? The latter test is the only way to check for insulation breakdown.

Blown496

I measured all the MSD plug wires. All were 24-26 ohms. I took the injectors out and am sending them back to the vendor to check out. Studying how this stuff works I know ltft is adding fuel to both banks to compensate for lean condition. When I drained the gas out of the rail it was very yellow. Odd. I pulled all plugs and they all look lean. No real differences. Just like the previous set. I buy 93 at the same place but now wonder how much actually gets bought there. Found a top tier station to use from now on. Could be as simple as bad gas but plugs don’t look like it.
or I have an air leak but you would think it would not change with new plugs. Accelerating will cover it up by adding fuel so a smoke machine or propane may be in my future.

1Hotrodz

You did not measure the ignition wire's insulation resistance or dielectric. This is the ability to contain the spark energy within the wire and not go to ground before it reaches the plug. What you measured was the actual resistance of the conductor itself.

Blown496

So that’s a test light to ground along each wire while it’s running. I’ll try it.

1Hotrodz

Not quite. If are you referring to a 12V test light then, no. This test uses what is called a Mega-ohm meter or a Meggar. It measures insulation resistance, hence the name Mega-ohm. Millions of Ohms of resistance. It's mainly used to check the condition of insulation on electric motors.
But it will certainly test a spark plug wires insulation resistance. Another way to tell if a plug wire is bad is: open the hood at night (must be completely dark for this to work) while the engine is running , you will see a Corona or even sparking around where the insulation has failed.

Blown496

Sent injectors in and three were leaking. Should run fine again when it’s back together. The ox sensors were going nuts trying to figure out rich and lean. Now I know why two cylinders on bank 2 and one on bank one were cooler at the header flange during idle.