Mystery problem solved!.... kind of

What the problems were: The engine would start but then the idle wouldn't catch and it would stall out. I had to give it gas when turning the key, and on the 3rd or 4th attempt the engine would idle on it's own. It would idle fine mostly, but would get short term episodes of very rough idling. When driving on the road sometimes the engine would lose power on and off as if I was pumping the gas pedal.

What I tried: With a helpful write up by birchlakeXJ, I started by looking at the throttle body and components. Everything was caked with carbon so I cleaned that up well. When I was testing the TPS (I had the power on/engine off) the fan was clicking on and off at random. I couldn't get good readings on the TPS so I just replaced the damn thing. I knew I had an electrical problem... I hate electrical problems, so I took it my shop.

What fixed it: The tech spent a couple hours troubleshooting and tracking down the source of the problem.... and found that the wire to the ASD relay was bad. It was corroded and was making spotty connection. He replaced it and now my Jeep starts right up and idles great.

So that fixed a couple issues, but sometimes when I;m driving down the road the engine still loses power in and out like I'm not pressing on the gas. It doesn't happen often, I'm thinking fuel pump but I don't know. Maybe injectors. The fun continues....

I've had everything from bad grounds to O2 sensors result in incomplete loss of power....miles? Mods?

OP--always post up your basic info--year, engine, etc.

Grounds are important, and absolutely CRITICAL for the Renix-era XJs.

Has anyone created a thread identifying all of the grounding points in the XJ?

Maybe there are too many of them to list, but I know grounds can do weird things even on motorcycles. On one of my bikes when new people have a problem the forums I belong to tell them to do two things ... Check GROUNDS + Tighten Battery connectors.

They list the ground points on the bike, but not nearly as many as would be on an XJ.

I'll do a write-up on the Renix grounds after propane peddling season is over , but I'll post something for ya now.

Two most critical are the engine dipstick tube stud and firewall to head.

Remove the nut at the dipstick tube stud. There will be 2 or 3 wires attached there. Scrape all the paint and crud off the stud til clean and shiny. Clean up the wire terminal ends til sotless also. Reattach and tighen the nut well. Add some dielectric grease to your refreshed connection to prevent corrosion.

At the firewall, remove the 15mm headed bolt that attaches that wimpy braided wire. Scrape the firewall area til thre's no paint and you see shiny metal. Likewise, clean the wire termainal and reattach securely. At the cylinder head stud end of the cable, do the same, scrape, clean til shiny , and reattach.

A good thing to do in addition to cleanikng the firewall ground wire terminations is to add a #4 gauge wire from the firewall attaching point to an intake manifold bolt, leaving enough slack in the cable for engine movement.

Want even better grounding? Add a #4 gauge wire from the negative side of your battery to the passenger side fender well. Recommended.

Wanna go all out and improve your charging system, charging system, and grounding system?

Contact 5-90 on this forum for a very comprehensive cable upgrade that is top notch and reasonably priced.

captain_k said:

So that fixed a couple issues, but sometimes when I;m driving down the road the engine still loses power in and out like I'm not pressing on the gas. It doesn't happen often, I'm thinking fuel pump but I don't know. Maybe injectors. The fun continues....

Click to expand...

My 98 does that occasionally as well but only on take off.