LS7 backfire initial startup E39 ecu

[TANKMASTERJ]

Ok guys here we go. LS7 with Late model racecraft cam and heads. Purchase out of a wrecked Z06 2008 model.
I converted to wet sump so I changed the timing set to a Katech while there and a melling high volume oil pump. Using a psi swap harness HAR-1037 and the gm E38 ecu that came with the wreck.
I got 59-60 lbs of fuel pressure.
It backfires a few times the first time I tried startup. Thought maybe the intake was sucking air since a smell a little fuel I think. ( My sniffer sucks since covid) but so I tightened intake some more. It fired up and sounded smooth at about 1500 then one more backfire.
I haven't scanned yet because my tech 2 was at my town shop and I'm home.
Any suggestions to start trouble shoot.
I'm new to LS but hot rodder and heavy quip mechanic for 30 years.
Advice needed.

[streetk14]

I don’t have an answer, but was it backfiring through the intake or the exhaust?

[ORBandit]

Stuck/plugged or questionable injector(s), plug/wire. Is the tune correct? If the tune is off that's another place to start. If it runs fine at 1500, i'll start with injectors. Good news is you have a GM ECU, so monitoring and trouble codes make it easy to problem solve. With a Holley Dominator, much more difficult.

[TANKMASTERJ]

Stuck/plugged or questionable injector(s), plug/wire. Is the tune correct? If the tune is off that's another place to start. If it runs fine at 1500, i'll start with injectors. Good news is you have a GM ECU, so monitoring and trouble codes make it easy to problem solve. With a Holley Dominator, much more difficult.
An aftermarket coil harness with two separate pluds and 2 wires flip flopped in each. It's all good now.
And I do got a GM ECU 38. For some reason my Tech 2 Scanner wasn't catching it bjt I didn't run it long.
Maybe that's why.

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I don’t have an answer, but was it backfiring through the intake or the exhaust?

Exhaust. But as posted below it was coil harness with wires flip flopped on 3 and 7. It runs fantastic now

[dhutton]

An aftermarket coil harness with two separate pluds and 2 wires flip flopped in each. It's all good now.
And I do got a GM ECU 38. For some reason my Tech 2 Scanner wasn't catching it bjt I didn't run it long.
Maybe that's why.

- - - Updated - - -



Exhaust. But as posted below it was coil harness with wires flip flopped on 3 and 7. It runs fantastic now
Nice troubleshooting. Things like that can be tough to find.

Don

[TANKMASTERJ]

Nice troubleshooting. Things like that can be tough to find.

Don

Thanks Don
I'm old to engine electrical on heavy equipment, dozer, excavators, compressors, cranes, etc, and multiple diesel trucks heavy and medium duty but this is my first LS swap so I'm learning alot.

[streetk14]

An aftermarket coil harness with two separate pluds and 2 wires flip flopped in each. It's all good now.
And I do got a GM ECU 38. For some reason my Tech 2 Scanner wasn't catching it bjt I didn't run it long.
Maybe that's why.

- - - Updated - - -



Exhaust. But as posted below it was coil harness with wires flip flopped on 3 and 7. It runs fantastic now

It’s not the first time I’ve heard of that happening to someone. Who made that harness, out of curiosity?

[TANKMASTERJ]

I cannot remember but I bought it quote a while back. It was supposed to be a USA one I recall.