theman637

Guys I could really use some help. I've got a 99 SS I'm working on for some ppl, they installed a new m6 trans and some off brand longtube headers that look like they are made really good. when they brought me the car it was backfiring like crazy more at idle and when I reved real fast, so I figured it needed a tune but they wanted a new cam and springs installed and the egr delete and all that stuff before I tuned it. after I get all that done and load the the tune with hptuners that I had from my dyno tune that had the same specs all but the header brand and it still backfires, it shows no codes I've changed all the sensors twice checked all the grounds,pink wires, intake leaks, exhaust leaks, moved coil packs,plugs and wires, fuel pressure, timing, new fuel about anything you can read about on any forum I've tried and nothing helps the funny thing is if I unplug the driver side coil harness it stops backfiring and doesn't change the way it's running but unplug the pside and it pops a few times and dies Dside header runs much cooler then Pside after ten mins of idling you can touch the Dside still I'm down to thinking the computer is junk but it runs perfect and has good power anybody have more ideas cause I'm lost.

Toes

iTrader: (1)

Kinda sounds like a cracked spark plug.

theman637

It done before i put new plugs in changed them twice now

G_rog

You can touch the entire header? Or just one runner??? Are they ceramic coated? Also you can unplug the driver side coils?? You got something weird going on there bud

theman637

Yeah the whole header is just warm on the drivers side yes I can unplug the drivers side coil harness and it stops backfiring and seems the run the same

joecar

Do you have another PCM to try...?

Check that coil wires to PCM are not damaged or shorting each other.

Check for leaky innectors.

JRENIGAR

iTrader: (37)

Any major blowby from worn rings?

Mazzenger

iTrader: (5)

Sounds like you not firing on all 8. Sounds like the driver side harness.
By chance could you have flipped the coil pack harness?
I would try flipping the driver side harness and try again.

Paul Bell

iTrader: (9)

Fuel injectors have two fuses, one per side.

Have you confirmed all eight ignition coils are making spark?

floman

iTrader: (54)

I would agree with checking this out. I had this exact condition on my LSX 427 engine swap where I did the coil relocation deal. I wound up getting the passenger side harness plugged in on the individual coils backwards. The engine would fire up and run, but two or three of the header tubes would only be luke warm after running and it would pop through the exhaust.

Swapped the harness around and engine ran great ! At least give it a look, could be a simple solution especially if you had the harness unplugged from the coils.