So I have a 2000 XJ Sport 4x4. I just got finished doing a whole gasket job on it (head, exhaust, valve, oil, thermostat, etc.) just to freshen it up while I had time over the holidays and it just rolled over 200k.

What I need help with is after I got it all buttoned up, I let it idle for about 30 minutes to burn any cleaners off, shoot out any carbon, check for leaks, etc. and there wasn’t a single problem. I drove it around the block that night and it did great. The next morning I let it idle up to temp then went to drive to work. About 10 feet after I pull out it starts stumbling and misfiring like no other. I limped it back and right before I pulled in my speedo went haywire and went to 120.

I ran my scanner and got codes for p0351 and p391. Coil pack and crankshaft/camshaft sensor. My question is what could cause this? Is there 1 ground that I could have missed putting it back together? My flexplate bolts were loose when I checked them so could a broken flexplate cause this? Any help is much appreciated and any other questions you have just let me know.

 

Check the wiring harness that goes behind the head for pinched wires. They very often get damaged in a head change. I had an 02 sensor shorted to voltage because of it.

 

I’m disconnecting all the plugs and spraying them with some electronic cleaner. The only thing I know I did was there’s a little ground on the back left side of the block that was all stuck together so when I took it off it twisted and popped a wire.

 

Yeah, those ground wires are pretty important, especially the ground strap from the back of the head to the firewall.