So, I noticed this about a month ago, but it happened very rarely. Last night it got A LOT worse, doing it at least a dozen times in 100 miles on the highway.

What it does:
The tachometer instantly hits 0, then bounces back up as the jeep recovers
The jeep jars hard (harder than just letting off the gas and pushing it again)
The lights and radio remain on.

So far the only time this has happened to me is while driving on level ground at constant speed (65mph) on the freeway. I have not noticed it being linked to bumps. My fiance said that it did it to her under load on a slight hill once too.

My guesses are that it is turning off (or cutting off) the engine somewhere just for a moment, then recovering, like a bad ground connection, bad engine power relay, or bad ignition switch. Any ideas where I should look first? How hard is it to replace these components?

I have a camping trip planned in a couple of weeks and I REALLY want to have this nipped by the time I go. Thanks in advance.

any ideas?

How can I test my ignition switch, or the wiring going to it? What other parts might be the culprit?

Does anyone know if the tach is controlled by the crank pos sensor, or something in the ignition system? I'm trying to figure out if the tach momentarily tanking might be CPS going out, or if it is ignition switch or main relay.

Someone out there has to at least have a half baked idea

Almost all vehicals tachs are controled by crank sensor. If you havent replaced it, I would now, it WILL die on you. The only other thing that might control it on this vehical is the cam sensor, under the distributor cap.

Ive had this problem myself. After i replaced the cps, i had this problem, especially after the engine heated up. It was in the connector plug on top of the intake close to the firewall. my 94 XJ has the GM connectors on it and the female connector side (engine side) would loosen up and not make good contact. I borrowed a plug pusher (for lack of a better name) and gently took the connector housing apart (small clip on bottom side) and the plug housing will come apart. Tighten the connectors slightly so they will have a tighter grip on the male connector side from the cps, and reassemble the plug. Plug it in and see if it still cuts out. This cured mine, although after a period of time it would start again as the connectors loosened up again. If mine does it again ill probably get tired of it and solder the wires together. Also as posted before the cam sensor plate can be a possibility also. My XJ will cut out after cranking it and if i popped the hood and pressed the connectors together, it would make contact and work. Good luck!

So, since it eventually goes out anyway, this is one part I can throw at my problem guilt free (I usually hate throwing parts at problems).

how hard is it to get to? Any good advice on getting it out?

Hey schadelh, I'm having the same problem with my 89 cherokee and mine is doing the exact same thing, I've notice mine will cut off randomly either when i start off hard on a hill or if i hit the gas hard, The guy i bought it from said it was the cps and it was going to need to be replaced soon but i took it to a mechanic and they said it was a bad ground somewhere cutting it off, they found my starter wasn't grounded very well and it would hit something and spark and cut it off for a half second and then sometimes it would keep doing it and cut it off completely. the starter was grounded better today and i drove it around for a while today, I tried starting off hard on hills and it never did it and from red lights hitting it hard and it never did it, It even turned over a set of 33's which it wouldn't before because of the cut off issue, But i'm not saying it fixed it! it could still be the cps but right now its not doing. So i would check to see if you got anything thats not grounded well. hope this works out for you.

+1 on bad grounding... had this exact same problem on a '95 Blazer..

I'd start with the ground from the battery.. Start by cleaning it, if that doesn't work, replace..

Got the new crank position sensor in today, and took a 4 hour drive with no hiccups. Looks like the problem is solved, hopefully...

glad I had my girlfriend around to help change that sensor. thick arms dont fit in tight spaces very easily.

Hope you are kidding! Universals and extensions....it's still a b-ch.

There are two camps of XJ owners.

*Ones that HAVE replaced their crankshaft position sensor

*Others that WILL BE replacing their crankshaft position sensor

The crankshaft position sensor is the most common engine management sensor failure on the Jeep 4.0 engine. If you lose the input signal from that sensor, you will not have spark and you will not have fuel going to the fuel injectors.

I'm getting ready to replace my crankshaft position sensor in my 2000 this weekend.

Same symptoms as the OP and everyone else on here. Sad this is before I found this site I replaced almost every damn sensor, full tune up (not a bad thing anyway) and about beat my head against the wall.

Shawn

Haven't gotten around to changing mine, but I have a new one, along with a socket set and crazy extensions in the storage under the seat, in case I get stuck somewhere..