Pranav catches the LT1 misfire zeka

[Pranav]

Great now I've caught the bug. Quick background:

-At NOLA in may, I would've sworn I had a tiny/faint miss above 4k RPMs. Then I dropped a valve and destroyed a piston.

-Pre-Hallet, new motor, 100% same ignition, fuel injectors were tested/cleaned, car seemed to dyno fine but high RPM looked a little janky on the dyno sheet; the dyno operator had goofed on hooking up the RPM pickup initially and the car still made the right numbers so we left it at that assuming it was the pickup

-At Hallet, after getting thru the wreck and rear end swap, I noticed I had the same miss from NOLA. Just enough to bug me but barely there. Went ahead and threw a new Delphi ICM on it. Made no difference

-Post hallet, took out all of the plug wires and checked them with an ohm meter; #3 was showing open/bad so I replaced it; all 8 plugs visually looked fine so I put them back in. Built a fresh opti and put it all back together. Also went thru and checked lifter preload. Some loosened a little, a couple tightened a little. Most were less than 1/8 with a couple being 3/8 turn from where it was originally.

Ran it on the dyno today and the operator could definitely feel that same miss, car was down 12-15ish HP and TQ and the high RPM graph looks jagged. AFR was solid at 12ish like it always is.

I need to double check, but I don't think I replaced the coil. How do I actually test a coil properly? I ohmed it before hallett and didn't find any conclusive results.

One other thing to consider; I left my digital dash on in the car over night so the battery was low before heading to the dyno. The dash is sensitive to voltage and will not turn on unless the battery has enough voltage, more than what is needed to start the engine; the battery was low enough to where the dash would not fire up with the engine off; it had to be running. At running idle it was high 13 on voltage and climbing after startup, right after the dyno pulls.

What else could it be? Going to try redyno on Monday with a charged battery and a fresh coil if I hadn't swapped it already, along with swapping/fixing anything else I may find this weekend.

[Supercharged111]

I went through hell with my car as you recall and I replaced everything but the knock sensor is what did it for me. I picked up around 20hp and my dynos magically smoothed out.

[marshall_mosty]

Check your mass air voltage and make sure it's not jumping around forcing the engine to chase itself. That is what it ended up being for me... I know mine is a Ford, but I think the LT1 uses a MAF...

[Sook]

Orange is spreading LT1 plague through the internet now! We tried to kill it with fire last week and it wouldn't die.

High RPM miss sounds like it could be the coil (plus they're cheap), may want to throw an ICM at it next. Any codes on the computer?

[Pranav]

No codes.

So far I've found the old coil ohms 2k-2.5kish more than a new one so I threw the new one in. Fuel trims seemed to add +2% but not looking at that too closely.

I just randomly yanked on the 2-wire coil connector and it would start to sputter and die as soon as I touched it. Pulled the backing/lock off the connector and one of the pins would just slide right out, not locked in place.

Could that have just been it? Still going down the list; I have 2-3 of everything and can keep throwing parts at it, would rather find the smoking gun. So far its been a bad plug wire; now I've found a weak coil and probably the coil connector.

[Sook]

I just randomly yanked on the 2-wire coil connector and it would start to sputter and die as soon as I touched it. Pulled the backing/lock off the connector and one of the pins would just slide right out, not locked in place.

I was having similar issues with the brand new coil connector on the new harness. Ended up cutting it off and replacing it with the original connector from the old harness. I hope that solves your problem.

[Pranav]

I hooked up my fancy opti signal analyzer and couldn't seem to find anything wrong with the opti signal at low RPM. I'll try it out on the dyno if I'm still having issues.

You guys need to check this stuff out:
http://www.1320electronics.com/OptisparkMonitor.html

Tomorrow morning I am replacing the coil connector and throwing on parts store plug wires, and keeping a parts store icm on hand for the dyno.

At this point my desire to get the car running right and tested in as minimal time possible outweighs my desire to find a smoking gun and not throw too many parts at it. If everything runs right on the dyno, I'll swap in ACDelco/Delphi parts and keep the house brand stuff as spares. I'll sell my other, used ICMs to you guys whenever you fry them at the track, since they all technically work.

Fortunately the dyno shop is a quick hop over from here, will try run it again Monday afternoon after work.

[BryanL]

Doubt it's your problem from Hallett but on the dyno don't rule out a weak/dead battery. I have had a few alternators go out while racing my ls1 and the first thing that happens is an upper rpm miss.

[Pranav]

Yeah I had it on a tender most of this weekend and the digital dash was having trouble turning on (needs higher voltage) until I got the car running. Flipping the ignition switch on it will intermittently not cycle the fuel pump.

I'm gonna test the battery tonight. I have a big arse boat battery I can swap in temporarily. It's funny because last year I had a battery start to get old and weak and not let the car start, but it still ran solid up top once I got it started.

When I swapped my plug wires yesterday, I found yet another bad plug wire. The theory of multiple bad plug wires beating up the coil also makes sense.

Prob won't dyno until tomorrow or Wednesday; they're booked up.

[ShadowBolt]

My battery is three years old and when I tried to start it up yesterday to drive it on the trailer I did not hear the fuel pump prime when turning on the key. Car would not start. Charged the battery for several hours and it started right up (fuel pump is priming). After backing the car and trailer in the barn I put the charger back on for three more hours. Battery shows 13.6 volts but only 62% charged. May be forced to purchase a new battery while at TWS I think it's on it's last leg.


JJ