1995 Backfiring through intake/popping.

[HopsnBarley]

OK, I'll start from the top. I have a 1995 Ford explorer 4.0 manual trans. It had a blown head gasket so I sourced a replacement OHV 4.0 with 130,000 miles and a good service history via the carfax on donor vehicle. I didn't trust any of the gaskets, so I replaced head gaskets, rear main, oil pan, VCs, etc. When removing the old cam sensor from the old engine to go in the new engine (new engine was out of a 96) I damaged the electrical portion of it, so I replaced the camshaft position sensor thinking it was no biggie. I was wrong. The initial startings ate teeth of the flywheel and killed the starter. I replaced the starter and flywheel, and then adjusted the camshaft position sensor per the manual. Now it starts and runs, but sounds like timing is a little off (slightly slower to rev) and after a few seconds of running will start to backfire through the intake.. makes a pop sound. After the initial pop it will start to pop over and over again, the pops closer together, blowing the idle air hoses off. Before they get too close together I shut the truck down. I'm somewhat lost as I have a lot of time wrapped up in this and although 90% of it has been post buttoning up the swap. If need be I can probably post a video of it but it has me frustrated and stressed. Fortunately it is not my daily driver but it is my only personal vehicle.

 

[arco777]

Check the plug wires are going to the right places. It is real easy to get them mixed up on the 4.0. They don't go the same order as the coil pack.

Otherwise see about resetting the cam position sensor...

 

[HopsnBarley]

No spark plug issues on this one, the truck actually runs somewhat smooth if you reset the PCM, you can rev it and everything but it sounds like timing is miles off. I've reset the Cam sensor a dozen times, with the same result every time.

 

[HopsnBarley]

I've continued to mess with this thing and now when checking my readings on the plug for the harness going into the plug, with the ignition on, I have 12 volts on the power wire, and 3.4 volts on the ground. WTF? Is there some really important ground I missed when I put this engine back in? I mean its ran for petes sake. When I plugged the harness back up, and back probed the plug with it hooked up to the sensor, I still have 3 volts on the ground, and about 1 volt less than battery voltage on the CID signal side. If I rotate the sensor, the voltage never changes, it stays constant at about 11 volts. I'm stumped.