Misfire Problem

OK... very weird,

Sister's STOCK XJ

94 XJ, 105K miles. No OR very little spark. Replace CPS, runs OK for a couple minutes, starts to miss again. Replace plugs, runs OK, then begins to misfire again. Computer gives NO CLUE, NO CODES, no errors. Seems like you do anything (perhaps time to cool) and it runs. Runs a bit then goes fluky.

I know it can be a LOT of things, but I am lost. Always fuel at the bar. Fuel doesn't seem to be the issue, more electrical/sensor oriented I'd guess but then again... I am here asking for help.

Martin, Eagle, Obi-Wan.... I need your help, you're my only hope.

My buddy had his 2001 with some 50k miles checked up, and a 4x4 shop in town says its because the Fuel Injection system is getting too hot and requires insulation.

oops: see you get no codes. His at least gets a multiple cylinder misfire code and a check engine light

kubtastic said:

My buddy had his 2001 with some 50k miles checked up, and a 4x4 shop in town says its because the Fuel Injection system is getting too hot and requires insulation.

Click to expand...

Which part of the system??

It could be some electrical component or connection getting hot. I've had trouble with a 93 that had a bad splice in the wiring harness to the injectors, which would start misfiring when it got hot. That one did throw a code, though the code was misleading, and it took a lot of troubleshooting to find the problem. One thing you might want to do to start would be to put a vacuum gauge on it while it's running. You can run the hose out the hood and tape the gauge to the side view mirror. Ignition problems will usually cause vacuum fluctuations, but a bad injector wiring harness (or a bad injector itself) will not.

If you haven't already, one other first step might be to get under the hood, and unplug and replug every single connector you can find. Do it a couple of times per plug, and check for corrosion too. Just cleaning those connections can help some problems.

This can be a real bear to track down, but it will help a lot if you can first figure out what general system is misbehaving. Once you have that, there are more specific tests you can do.

I think the vapor lock problem cited above with the 2001 is not usual with the earlier ones.

bttt

The 2001 issue deals is pretty much limited to that model year; I think it was specifically Injector #3 that's involved. That's been covered here a number of times but I didn't pay attention to it since it didn't apply to me.

The plugs and/or wires haven't been changed recently have they? Somehow I've got a picture of the firing order being wrong...