backfiring 2.9

[junkfixr]

Kinda long story so I'll keep it simple. I put an 86 2WD cab on my 87 4x4 chassis. All of the wiring & connectors matched except for a couple of issues.

1. The 87 has a wire going to the transfer case with the speedo cable.

2. The plug for the Oxy. Sensor was larger on the 86 & wires were different color coming from the harness.

I spliced in my original plug to connect to the Oxy. Sensor after studying the wiring & just left the speedo wire disconnected as the 86 harness didn't provide a connector for it.

Everything worked out well (lighting,wipers,fuel pumps,etc.) but now I have a backfire through the exhaust. Unplugging the Oxy. Sensor made no difference at all. I swapped out the ECM under the passengers kick panel and that made no difference. It doesn't seem to do this at a high idle and it revs up with no problems. It seems to pop more at low idle.

Another fact...the 4x4 sat for about six months untouched and I'm wondering if contaminated fuel could cause this, or maybe a stuck valve ? The longer I ran the engine the more it smoothed out, but the backfire isn't completely gone. I still have the original wiring harness from the 4x4 but before I swap that out I was hoping to get any input or advice the forum may have to offer.

Thanks in advance...Kevin

 

[jhammel85]

Usually it's timing. Have you checked it at all? It might very have something to do with what you swapped but I'd start there.

Make sure to pull the spout plug!

 

[junkfixr]

haven't checked timing

but I do know the engine was running perfectly before I did the cab swap. I noticed today that the temp. coolant sensor plug on the 86 is slightly different with different colored wires.

I'm wondering if there is a difference in the wiring harness on the 86 vs. the 87 models ? It idles as if 2 spark plug wires are crossed. I did notice that the distributer on the 86 was greatly advanced compared to my 87 but I assumed it was due to slop or wear in the timing chain.

Could the change in computers and wiring make a difference in the position of the distributer ?