Noticed tonight coming home on a back road that holding about 50 mph, there were several "misses" or hesitations where it felt like the engine would cut off. Only happened about three times but very noticeable. Absolute stock set-up. Any idea what could cause this? Thinking maybe a coil pack breaking down or a bad plug wire. Sounded and felt like an ignition or electrical issue because it was so abrupt and brief. Then it stopped doing it until about another 5 minutes later.

 

Probably not a single plug wire. That wouldn't be very abrupt.

Things like failing cam/crank sensors and failing fuel pumps can cause the type of problem you are describing. And of course these items can have problems due to failing electrical connections or wiring problems. When it is intermittent and only while driving, they can be particularly difficult to pin down until they become a little more predictable and severe (ie. reproducable).

I don't like the parts canon approach, but sometimes for these types of problems you can begin swapping out the components that are oldest or that are most suspect, and the if the problem does not go away you simply keep the replaced component as a known-good spare.

Coil, cam sensor, crank sensor, fuel pump, cap/rotor, and o2 sensor are all candidates I'm afraid.

 

Crank sensor is the most likely culprit if it's cutting in and out like you turned the key on/off real fast . When they fail, they either outright die and won't start or become weak and start cutting out when they get hot. If you haven't already, head over to cruiser54.com and go through the list of tips, especially the ones about the grounds and cleaning or eliminating the C101 connector. There was a TSB and a kit to modify the crank sensor wiring to go directly to the engine computer, but I think refurbishing or eliminating the C101 connector is all that's needed.

edit - Also I believe a failing camshaft sensor will not cause cutouts once the engine is running. The renix era computer just uses it to initially figure out which stroke it's on and then uses just the crank sensor after that.

 

I had a similar issue not to long ago. It turned out to be the ignition coil was bad. I would be driving down the highway and would have the same symptoms. Everything would operate correctly until the engine heated up after about 15 minutes of driving. My coil had what looked like hairline cracks in it. After I pulled it off the engine the cracks were way worse than I could tell while it was still installed.

 

If I had an 88, I would go to www.cruiser54.com and complete tips 1 through 5 before doing anything else.

 

Excellent site and plan to attack these first. Being a newbie to the XJ group, educate me please, as Iv'e heard the term Renix a few times. What exaclty is Renix?

 

Thanks for the tip on cruiser54. I will also take a look at the crank sensor, as I got a better feel for the issue today. Traveling along at any sped under 55 and it does not occur, but once warmed up, it continually happened at the 55 mph mark. Almost felt like the transmission was shifting repeatedly and seemed to happen more at I began to let off the gas.

 

Renix comes from "Renault/Bendix" - manufacturers involved with Jeep production in the late 80's.
The Jeeps from 87-90 used a lot of stuff that is unique to those years (the electrical and cooling system come to mind.) Hence these Jeeps are often referred to as "Renix" Jeeps.
When Chrysler took over in the 91+ model year, you get the design that was similar for 91-01.
The engine and body design as well as the suspension stuff is pretty similar though from the mid 80's through the last XJ model year 01.

I had cracks on my ignition coil that I couldn't see until I replaced it - and it definitely ran smoother with the new one.

 

The 90->91 change also included changing to the HO version of the engine, which for the most part was just changes to the intake manifold and the electronics.

 

Thought I would go ahead and replace the coil since it looked original, no cracks though. Found one locally hooked it up and the engine turned over ponce and sounded like it would start and then died. Now won't start at all. Obviously the new coil isn't working, putting the old one back in and then back to cruiser54. Hopefully domething didn't fry with the new coil.

 

Thanks.. New coil doesn't work at all. Still troubleshooting.

 

I would check the fuel pressure at the rail. The tester is available for free rental at O'Reilly's.

 

Don't bother with the cam sensor! On Renix you can unplug it and it will run fine. (it helps the puter figure out #1 from #6 starting is all). Good advice above ^ Hey, just for giggles see if it does anything weird in 3rd. Your torque converter intermittently locking might be the issue, and so, so, easy to test that! (driving in 3rd). There's a second switch on your brake pedal that unlocks it. Besides the switch, it's wire through the C-101 connector needs to work BTW.......

 

whoa........... which Tips have been completed so far?

Plugs, wires, cap and rotor are to be replaced every 30,000 miles.