As in the title, I don't have an idea of what is wrong, but its a 98, and I was driving it the other day and all of a sudden it started running weird while I was driving it would be running fine until I started trying to go faster which was about 55 mph and it started studdering and It kept getting worse and about 10 minutes later when I stopped it got so bad it was misfiring really bad, so I did a tune up, plug wires, cap and rotor and I have new plugs as of about 3 months ago and it didn't solve it so I used a computer to see what was going on and did a misfire test in about 3 minutes the lowest misfire reading was 89 in cylinder 1 and the highest was 256 in cylinder 2, so I replaced the cps and it made it better but if hit the gas from idle it misses and sputters and then it takes off, and sounds fine, if I'm driving it will misfire really bad above 3500 Rpms, any ideas also tried a new map and tps

 

A known problem on a `97, may happen on a `98 too. Check the injector wiring harness between the firewall and engine. If it is touching the engine anywhere, tie it up and away.

Here's my original photo and you can make out the fuel rail mushed into the wire harness:


This closeup makes it very clear:


Simply moving the wire harness from this pinched location eliminated my high speed misfire.

Since tying the harness up away from the engine, my XJ has run perfect for several years.

 

I have already tried to move wires around that was the first thing I did try actually

 

I am almost thinking its a fuel pump because how bad it runs, I tried to squirt something in the tb and it seemed like it was running better, ill try to find a fuel pressure gauge and see what its running

 

Checked fuel pressure and its holding 48 pounds, it doesn't hold it for long when I shut it off though I don't think it has anything to do with it though but it starts fine when its cold and as it warms up it will start misfiring more and more and then it will just start misfiring so bad it will finally die...and ideas???

 

The first thing you should do is run it for any codes. Even if the CEL isn't on you may still have stored codes. This will give you somewhere to start instead of going in circles.

 

That was the first thing I did, no stored codes or anything

 

Whats fuel pressure at when it stumbles and dies?

 

At 48, it doesnt move from that until it gets shut off then it will drop

 

And no codes at all?

 

None at all

 

FIGURED IT OUT!!!!!!!!!!!!! It was my accel coil took a crap!!!!!

 

Have the same intermediate problem, seems to be only when it's muggy/hot out. Changed all the plugs, wires, etc as well. Beyond annoying, I'll check for that fuel, wire concern as well

 

Check your coil or injectors if its missing

 

Really? And we catch so much crap from people when we recommend they not use any fancy-dancy coils on these Jeeps.