Seymor Butts

iTrader: (1)

So I'm completing the swap on my 68 Bird. The engine is a LQ9, stock never even taken apart. I've got headers on it, that are mated up to an exhaust that just has some mufflers and that's it! I also have FAST Fuel Rails on it. PCM is off a 4.8 2001 Silverado, the engine is a 6.0L 2003 Escalade.

Any idea what would cause the crazy loud backfire? Supposedly it shoots out flames I was told. It's as loud as gun shots. Not normal for sure... Do I need a tune when running headers and fuel rails? Otherwise fuel injectors stock. 255 fuel pump. 6AN fuel line.

PCM was bought from the company that made my wiring harness. I know that they removed the key immobilizer stuff off the PCM, programmed the tire size and rear end. Not sure if they did anything else.

I also have a P1336 code which I couldn't get done the other day with my friend's high end Snap On. It would just get stuck in the middle of the process..

Seymor Butts

iTrader: (1)

Some more info...

It seems that it only backfires on the driver side exhaust (I do not have a cross over which is how I can tell). It literally shoots flames out the pipe. See video uploaded just now (note the whirring type sound you hear is the intake fuel pump):

bczee

iTrader: (12)

Try some new plugs or swapping them from the other banks. also swapping the Coil pack from the other side.

could be a broken plug, wire or coil.. Those would be my suggestion.

Check the wiring connectors and harness of the coil packs. Have you also check the valve train ? Bent push rod or valve, check for broken spring ?

good luck with it. hopefully it will be something simple. I spend some time chasing my mis-fire / Backfire.. turned out to be a hair line crack in one plug.

BC

Pop N Wood

iTrader: (1)

Almost certainly an exhaust leak. I once had a car with an exhaust air pump and a bad A/B valve. I use to purposely get on the gas then let off making it backfire in the Sepulveda tunnel under LAX. Every car in the tunnel would brake.

Old Geezer

iTrader: (3)

Data log it....
Did the engine sit for an extended time, B4 you installed it and started it?
Sounds like there's a fuel leak into the exh, such as an inj stuck/leaking.

Seymor Butts

iTrader: (1)

Thanks all for the suggestions.. Looks like the wire harness for the driver side coilpacks was pooched. Luckily I had a spare sitting around, plugged it in and the car stopped backfiring. The idle is still a little crappy and I couldn't figure it out. It just sputters now when driving along - feel like its a timing issue now. I dropped the car off at a local shop to get it looked at for their opinion.