88 renix motor not starting when hot

I've read numerous threads about this issue but I have a different situation. First off, I have a 88 XJ with the 4.0 Renix engine and a 5 speed manual trans. We did the typical tune up to it when we got it. Spark plugs, cap and rotor, wires, replaced al the vacuum lines, etc. etc.

Recently I changed the TPS because of a bad/fluctuating idle and because it tested out bad. I got it all set up the specified specs. Thing runs much better upon start up, idling and cruising.

This new problem occurred the day after I got the new TPS installed. It will fire up just fine when cold, runs great, then if I shut it off for 5 minutes the thing will crank but won't fire. If I let it cool off it will fire up again and run like nothing happened.

I've read about the CKP sensor being an issue but I measured that with the motor warm and it measured at 245 ohm's which is within the specs. I've also read about the CMP sensor being an issue. I do have the correct voltage to it however I don't have an analog volt meter to check if the stator is working properly.

Again, this no start when hot problem started right after I replaced and properly adjusted the TPS. I know the computer uses signals from all sensors to make it run, is it possible the old TPS was masking another problem?

The truck does have almost 350,000 miles however I know for a fact that its been rebuilt at least once before. I'm not sure what sensors or components have been replaced before I got it. Any input would be great thanks.

Correction: I only have about 2 volts tested at the distributor connector. I was able to borrow an analog style volt meter to check the stator and I have zero fluctuation of the needle meaning I'm getting no sync pulse. Looks like i'll be installing a new CMP sensor this weekend. Hoping to get all the gremlins out so my son can enjoy his ride!

Ok, installed a new distributor. When cold, it started way faster and runs a whole lot better. However....
After it is hot an I shut it off for 5 minutes, it only cranks and won't fire. Same problem as before. I retested the crank possition sensor after it was hot and got 269 ohms. Seems pretty close to the 275 limit. It seems like when crank sensors fail the thing just shuts down which isn't what is happening to me.

Any ideas???

typical cps failure is hot. They wor for a time, get warm then go bye bye until they cool again.

Since it started faster I'd say the cam sensor was probably bad and the ECU was guessing at cam position.

you need to check for spark when it won't start. If no spark, I'd strongly suspect the CPS or the ignition module. Ignition modues don't fail often, so CPS would be my first suspect.

I do have spark when it's cranking. I think I'll probably replace the crank sensor just to rule it out and since they're a common problem. I also tested my coolant temp sensor and got .750 ohms resistance which isn't even close to what it should be. Probably going to change that too...

See Tips 1 through 5, and 27 in the link below.

http://www.naxja.org/forum/showthread.php?t=1115935

87manche, thanks for the tips. I still find it very odd that this problem only started happening right after I changed the TPS. We've had the Jeep for a couple years now and while it always ran a little rough it would still start every time...I guess its the curse of an older vehicle, fix one thing and 3 other things break.

cruiser, thanks for the post, I'll run through the list this week.

if you have spark it's not a CPS issue.

ECU won't pop the coil without a crank signal.
do cruiser' tips.
Check the fuel pressure. pump could be weak, or have a bad ground.

That's kind of what I thought. I'll verify fuel pressure and go down the list from cruiser

SOLVED!!!

I finally got it... Turns out that new TPS that I bought from O'rielly's was malfunctioning when it got hot. I don't know why I didn't check it after the problem started, I guess I figured that it was new so how could it be bad. I guess that goes to show the quality of parts from O'rielly. I am going to order a new one from Napa to be sure I get a good part.

I did run down the list from Cruiser and doing a lot of the things on there really helped the way the truck works now. Getting rid of the stupid connector on the firewall seems to have helped a lot.

Thanks for all the help guys!

Great news.