Yesterday I was heading out to go camping when I hit a pothole and my xj misfired (momentary power loss, rpm loss, and slow down) and a check engine light for about 1 second and then it ran normally. Once I hit the dirt road with every hard bump (every 2 minutes), it did the same thing and it backfired a few times too. If I hit a few bumps in a row within a few seconds of each other, it stalled out. Only once though.

The next day on the way home it did the same thing. When I got home I checked the wires on the ignition coil and the spark plug wires (new plugs and wires 4 weeks ago) and can't find any exposed wire. One plug wire was loose but I seated it and test drove it off road and the same problem still happened. The plug wire didn't come loose again.

I plan to check the grounds, but I'm not sure where to check (which ones and where they are located)

I have a cracked aftermarket header (Chinese made) I took off and had welded last week and places back on but it re cracked. I am replacing it tomorrow with Gibson headers. All plugs and hoses are properly connected.

Any suggestions where's else to check or what it can be? The search function doesn't work too well for be on the phone.

 

It doesn't have to be electrical. I had a similar problem on one of may cars. It was lose suction manifold.

 

I'll double check that tomorrow when I install the gibson headers but I torqued to spec and re torqued two days later. And I used copper gasket sealer to hold the gasket on both sides. I'll check for any cracks or uneven ware or loose bolts etc...

Another weird thing it just did after posting is my fuel gage dropped to E and my light came on and my overhead said 0 to E but it gradually climbed back up to where it originally was. I filled up and sure enough it only took about 15 gallons to fill it. It didn't happen again. Not sure if related or not.

 

Funny thing with the fuel gauge. EXACTLY the same happened to me a few days after I bought my XJ and also, it hasn't happened again (15,000 km so far). There were no other adverse effects at that time, so my GUESS would be, it is not related. Good luck sorting out the problems!

 

Bad ground to the fuel pump/gauge unit. Or a bad connector.

 

Ok. An obvious starting point that I'll look at for sure. Think its related to the mis fire (maybe from lean fuel from the pump cutting out) and the check engine?

 

Quite likely.

 

Replaced header with gibsons but haven't been on a rough enough road to test the problem. Checked around the fuel pump and the wires but didn't feel or see anything bad.

 

Ok. Been out a while but I'm back. So I the problem never went away. Any sudden hard bump and the check engine light comes on then off for 1/10 of a second. The RPMs drop. Sometimes it back fires and sometimes the fuel guage drops to E instantly then alowly climbs back to its original level, but a NEW development...sometimes the RPMs shoot up! I'm talking from 900 or 1000 at idle to 2500 or 3000 at idle and then 2000 or 2500 in drive/neutral/reverse. If I hit a hard enough bump it seems to correct it (still with the other symptoms though ). What in the Hell is going on here? Was sure it might be a loose ground connection but the climb in RPMs from a bad ground????

 

Have you addressed the grounds at all? Like finding them, removing them, cleaning and reattaching them? The whole system works pretty much on variable grounds......

 

I hadn't yet. That's where I was going to start when I had the time but the ride in RPMs throws me off unless a ground is bad on something that would limit the RPMs thereby removing that restriction and allowing the RPMs to jump up.

I haven't even had the time to find out where all the grounds are, how to get to them, what they correspond to, etc...

 

Perhaps someone with a FSM will give you the ground locations.

 

True.


Anyone out there happen to have one? A digital copy would be great but if you can only let me know the locations that would be ok too. Anything helps.

 

I ACCIDENTALLY fixed it! So today I was hit bad with the backfire and check engine. Every little pebble on the pavement was setting it off. Couldn't get over 5mph. So I went to re checking EVERY connection and ground and wire and vacuum and so on. I took off all my plugs and checked the gaps, increased them to about 40-42 instead of 35 to see if there was a difference. Plugged em all back in. Checked all my distributor wires. All good. Found one exposed wire to the tranny but it was the factory cut. Taped it anyways. Yadda yadda.

After feeling defeated again I went to start it up and it was all crank no fire. I cursed the gods and went to checking my plugs again. Jiggling the wires from 1 on to 6. When I got to 5, I jiggled it and my fan came on. Odd. So I made sure it was snug and tried to start it and no fire still. Went to jiggle it again and fan on again. Went to jiggle 6, same thing. When I went to move some connectors that I had already checked out of my way, BOOM fan on...wtf?! So I looked closer and there was a big connector hidden back behind the block a little. It was loose! I snugged it up but felt no bite, no click. Cris crossed some zip ties on it and drove a half mile to a logging road and hit some big ruts and NO BACKFIRE NO CHECK ENGINE! If I'm lucky that was the only culprit!!

Feels a little sluggish but maybe from the increases gap. Still better than it was!

 

Oops