1994 YJ Help! Is the computer the problem

Its not a 4.2L it a 2.5L I-4 Sorry...

You know, the ignition control module is a rather cheap swap out, looking at the list of stuff you have done. I had an 87 YJ 6 cyl that had mysterious problems with cutting off and not starting when warm and such. Putting in a new ICM made it all go away. In 2000 it was about $65US in the NAPA parts store. The odd part was where it was located - in the wheel well on the other side of the sheet metal from the engine (on the tire side). Just unbolt it from the sheet metal and unplug it - that is it and you can do it yourself.

Stay tuned for other thoughts here, but this is what worked for me back then. Hope this helps, Tomes

The 4.2 is a carburetor engine so you are going to get all kinds of wrong advise....

You later state it is a 2.5.....

I would be suspecting the electrical connections on the throttle body. When they get corroded, the gas pedal response can act like you describe.

The pins are very small computer signal pins and can look perfectly clean but be corroded enough to interfere with the signal.

I recommend a good clean of every sensor connection you can get your hands on with a spray contact cleaner. I then use dielectric grease on the plug's seal skirts. The best spray is sold at electronic shops, but in a pinch, WD40 will work as an electrical cleaner.

I would try the clean before tossing any expensive parts at it.

A massive vacuum leak at the TB is just plain bullshit I am sorry to tell you. A vacuum leak at the TB causes 'high' idle, not low idle, they lied to you.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >

Thanks for the suggestion, but my problem is still there. I made it

11.4 miles this time.. I got some c> The 4.2 is a carburetor engine so you are going to get all kinds of > wrong advise....

Did you have your fuel pressure tested yet???

When you first start the engine, it will run fine but after 10 or 15 miles your fuel pump might be loosing fuel pressure. I would put a guage inline and drive around. Check it cold and after 10-15 miles.

How about the gas tank vent on those? That would be the charcoal canister... If you open the gas cap and it goes whoosh and then it runs ok again, the air filter on the gas tank vent is plugged up with mud or dirt or just too old.

On a 94... Gas filter? Does it have one on the frame rail just in front of the tank? If so, I would change that too....

Worn away new HT wires, as in pleural!!!!! Say what????????

That just plain isn't supposed to happen. Ever. Something is seriously wrong with those wires....

If the core was exposed on the coil wire or any other, they are dead wires and need to be replaced. If the insulation is falling off, it didn't cure or was a bad mix or something.

I would just plain take those wires back and get new ones. That could be all your latest issues.

Mike

aj wrote:

I replaced the fuel filter still the same problem. I also checked gas cap for the whoosh no whoosh.

I am not going to be able to work on it again until this weekend, gotta go back to work so I can pay for all these sensors. I will be checking the fuel pressure this weekend. If thats not it guess the next sensor will be either the camshaft position sensor or the crank position sensor? I did think about the crank position sensor. Everything I have found so far says you won't be able to start with a bad crank sensor. I am currently able to get it started, give me some time and I am sure I can make it not start.

Thanks again for all the help, If you have any other ideas I am more than willing to give them a try.

Were I a betting man, my money would be on the fuel pump, but I work too hard for my money to burn it up gambling.

Before you pony up for a CPS and go through the pain of replacing it, grab a Chilton's and see if there isn't a diagnostic you can run on it with an ohm meter. For some model years you could check it and see if you were getting the couple of hundred ohms the spec called for.

I gather that usually when the CPS goes it is dead dead dead. You get no spark and no fault codes (at least in older models) -- because the computer doesn't know the engine is spinning over. But something I read recently was about finding an intermittant break at the CPS connector -- in one position it would run fine, in another the wire would open up just enough to make it run crappy and stall frequently. Just something to keep in mind.

aj wrote:

Its fixed! It was an intermittent Crank Position Sensor. It didn't set a code and tests with an ohm meter were within spec. Since it was the cheapest of all fixes in my current list of guesses I figured I would try a new one anyway. Went to the parts store got a cheap after market - figured it would work well enough. Crawled under the jeep with my socket wrench. Now for the interesting part, when I went to loosen the bolts, those bolts turned Real easy. Not finger tight but it sure wasn't the 14 ft. lbs. of torque suggested. Once I got the CPS out I found very slight scores on the face. Not knowing the tolerances between the sensor and the flywheel, I can only guess that it had contacted the flywheel at some point. Since these things seem to be really sensitive, I suspect because the sensor was loose it would move out of position. Then the computer couldn't figure out what was going on. I can't explain why it seemed to be only after it warmed up (all but one time).

One good thing did come out of all this, my jeep has NEVER run as good as it is running right now. I have a hard time not turning the tires over at the stop signs. I don't know if I am just not use to all this new power or that there is a 1/4 inch of ice on everything up here in Vermont ;)

Hope I am able to return the favor some day. GoodOnYa...! All

aj did pass the time by typing:

14ft.lbs actually isn't that much torque. It's about what you use to set spark plugs.

The tolerance is set by a bit of cardboard that's usually stuck to the face of the sensor. Some have it, some don't. The ones that don't have bolt holes that have no slop. I have no idea what the spec is on that sensor.

When the computer moves from warm-up to operate mode it uses different sensors. It could be that what ever the problem was that switch in operation masked most of it.

Good to know. Glad you got it fixed.

That dang CPS sensor is the most common issue with Jeep it seems.

It's that lead brick attached to your right foot. :)