V6 LS3 (2 dead holes).

[416velle]

So it took me a long time to actually visualize and formulate this hypothesis, but I now have almost 100% certainty the reluctor wheel is not my issue



The 4 stroke cycle requires 2 rotations of the crankshaft to complete its firing order. That means on any 1 given location on the crankshaft during its rotation (of any engine more than 2 cylinders), theres 2 different things happening. In my case, I """MAY""" have a problem on the equivalent of the intake stroke of cylinder 8 AND another at the intake stroke of cylinder 6....Well, give that crankshaft 1 full rotation from either of those locations, and cylinder 8 is on it's compression stroke, while cylinder 5 is on its intake stroke, and likewise when 6 is on its compression stroke, cylinder 1 is on its intake stroke. This suggests any given chipped tooth/damaged gear on that reluctor would yield an IDENTICAL FAULT on the cylinder that's exactly 1 revolution off in the firing order. I DO NOT have problems with cylinders 1 and 5.
This alone strongly suggests I have an internal ECU failure, given I have completely exhausted all my troubleshooting options at this point.
It is late and my brain is fried so I may be way off my rocker.

[Big_KID]

Have you pulled the valve covers and rotated over by hand to confirm the valve event order is correct for 6 and 8? It is a long shot but cam could have lobes for 6 and 8 swapped placing the valve events 135/225 degrees out.

[416velle]

Updated firmware for giggles.....nothing.
I messed around a bit with the datalogging feature to look at the pulse width of the screwed up cylinders when the thing is running.....according to the software ALL injectors are at IDENTICAL PW and lb/hr values.
NOW...when i adjust the individual cylinder fueling parameters of 6 and 8, the frequency of the backfires changes significantly, and the datalog does display the correct % changed values when idling....likewise with adjusting the timing. I contemplated switching 6 and

So at this point, if I trust the ECU, that means I err towards reluctor wheel being the failure mode here (somehow). Which kind of lines up with the symptoms at hand, and the ECU values corroborate that to an extent. If spark isn't at the right time this will happen. So this means I have to pin my engine harness for the coil side?

After some thinking and drawing, when 8 is at TDC of compression stroke, 6 is in the middle of its intake stroke and vise versa. I am about to switch 6 and 8 even though I know they're plugged in right because why not and at this point if I blow it up itd be a god send and I can have an excuse to put a different motor in it that doesn't have an ECU or a reluctor wheel

- - - Updated - - -

Have you pulled the valve covers and rotated over by hand to confirm the valve event order is correct for 6 and 8? It is a long shot but cam could have lobes for 6 and 8 swapped placing the valve events 135/225 degrees out.

That's a good idea and I'm game for it right now.

[416velle]

Valve events checked out fine, and I did swap 6-8 [plug wires] only for backfires to occur through the intake instead of the exhaust

[416velle]

Took a video yesterday of the reluctor straight-on through the crank sensor hole: No runout, no bent teeth, it looks fine.
Today I'm going to use my graphing multimeter and read the waveform of said reluctor and compare it to samples online.
I'm at my wits end here, holley doesn't answer their phones or emails (2 hours on hold) and the one time I did get through, he said "theres no way for you to test the ECU to see if its dead".
If the waveforms are the same then Im ditching the Terminator X and putting a pro-flo 4+ or XFI in the thing. I'm 3 parts away (indlucing engine) from driving this GD car out of my driveway. EXTREMELY frustrating

[416velle]

FOUND MY ISSUE. NOT ECU. ITS RELUCTOR. ANY1 HAVE EXPERIENCE WITH CRANK TRIGGER KITS??

So basically what I did is swap injector plugs AND coil plugs between cylinders 4 and 6, and changed the firing order in the tune to 18724653. This effectively uses cylinder 6's electronics on cylinder 4, and vise versa. This was useful because it tells me that IF the issue FOLLOWS cylinder 6's electronics to cylinder 4, then I have a ECU issue. And contrarily, if the issue stays at ACTUAL cylinder 6 which is using cylinder 4's electronics, then the electronics are OK I have a timing issue SPECIFIC TO ACTUAL 6-8 which indicates a reluctor wheel problem. I'm DEFINITELY not pulling the motor out and apart to service the reluctor wheel.

[pannetron]

Sounds like an ignition harness issue to me. Not sure which ignition harnesses you're using but the GM harnesses are side specific.

[416velle]

I meant to close out this thread with my findings a month ago when I fixed the motor............Found the issue! Engine is in perfect running order now.
Some goofball (me) who built the car installed the bank 2 coil sub harness backwards. THATS IT. Fired RIGHT up after I figured that out.

I did get some good practice with a lab scope in determining my crank and cam signals are completely mint. Lol.

Note to self: when taking stuff apart, know where it came from before putting it back together. I messed around with relocating my ignition coils to the firewall, and flipped one of the harnesses to give them a mirror image look on the firewall. Well, i didn't number which one came from which cylinder before doing that.
I appreciate all the responses fellas, have a great rest of your day

[andrewb70]

I meant to close out this thread with my findings a month ago when I fixed the motor............Found the issue! Engine is in perfect running order now.
Some goofball (me) who built the car installed the bank 2 coil sub harness backwards. THATS IT. Fired RIGHT up after I figured that out.

I did get some good practice with a lab scope in determining my crank and cam signals are completely mint. Lol.

Note to self: when taking stuff apart, know where it came from before putting it back together. I messed around with relocating my ignition coils to the firewall, and flipped one of the harnesses to give them a mirror image look on the firewall. Well, i didn't number which one came from which cylinder before doing that.
I appreciate all the responses fellas, have a great rest of your day

I just had the exact same thing happen with a customer. His driver's side coil sub harness was made wrong by a vendor (not Holley).

If I can be of service with the tuning, please email me: projectgattago at gmail dot com

Andrew

[Jeep9783]

I meant to close out this thread with my findings a month ago when I fixed the motor............Found the issue! Engine is in perfect running order now.
Some goofball (me) who built the car installed the bank 2 coil sub harness backwards. THATS IT. Fired RIGHT up after I figured that out.

I did get some good practice with a lab scope in determining my crank and cam signals are completely mint. Lol.

Note to self: when taking stuff apart, know where it came from before putting it back together. I messed around with relocating my ignition coils to the firewall, and flipped one of the harnesses to give them a mirror image look on the firewall. Well, i didn't number which one came from which cylinder before doing that.
I appreciate all the responses fellas, have a great rest of your day

Digging up bones here but couldn't find a way to message you. I am having same issue except on cylinders 2 and 4. Built my setup (5.3 cammed etc holley term x max) drove for 350ish miles until it started skipping and found cylinders 2 and 4 misfire. Changed all coils, all injectors x2 with Holley, installed new engine harness, spark plug wires and plugs. Same issue, pulled heads and lifters all good, checked heads also no leaks. Forgot to mention comp test prior to all of this and was good. I have fuel and spark but using heat gun 2 and 4 ain't doing nothing. Mine is a rock crawler so not a touring but so far ur post only 1 close to mine. BTW what harness did you have backwards and any cheat codes you care to send my way as May will be 2 years I been working in mine.