No start when Hot

[96TNXJ]

I looked!! I know its here I saw it but cant seem to find it now :wow:

I got a 96 4.0 lifted 6.5 on 33s with 355 gears. When I drive it long ways (30 to 45 mins) and its hot outside it wouldnt start when you turn it off. It runs fine till you turn it off and after you turn it off you have to wait 10 to 15 mins then it will start right back up. Around town (5 to 10 mins) of driving I have no issues

Like I said I know its here I have been looking for about an hour with no luck. Sorry if thats not long enough but I am off tomorrow and am wanting to come up with a few things to check. TIA

 

[JJacobs]

You might have better luck with this in the OEM tech forum. Anyway, what happens to the fuel pressure when you shut it off?

 

[96TNXJ]

Thank you for moving my post and sorry for posting in the wrong area

 

[birchlakeXJ]

Assuming no check engine light? If so, pull stored codes for guidance.

To confirm. It never just dies/stalls on you, just won't start sometimes when engine is HOT right?

First thing that comes to mind is the camshaft position sensor. If the cam signal is lost while the engine is running, the ECU will calculate spark timing based on the last cam signal and the engine will continue to run. However, the engine will NOT run after it is shut off.

The cam sensor is located inside of the distributor on your 4.0 engine. It can be tested with a manual and a meter but know that if it is suffering from thermal (heat) failure, you would have to test it WHILE the engine doesn't start. Testing it when the engine runs would probably be of no value.

Good luck and let us know what you find!

 

[89xj]

when it doesnt start, do you check for fuel or spark???

temp related could be a bad coolant temp sensor, which feeds the pcm.

other possibilities could be thermal break down of the coil or cps.

 

[96TNXJ]

I was thinking it was the thermal break down of the coil

and no there are no codes at all

I dont think its a fuel issue due to Im able to here the fuel pump running and I have pressure at the fuel rail

No it does not stall or die on me when its hot it runs find it just wont start back up when its to hot

 

[old_man]

If it sputters when you try to start it, do a search for heat soak. There was a TSB on this, but you can fix it yourself easily. If you need some aluminized wrap, shoot me a PM and I have a huge roll I can cut you some off of and mail it to you.

If there is no spark at all, witnessed by pulling a plug and laying it against the block, then my bets would be on a CPS or a bad coil.

 

[96TNXJ]

I forgot to tell you all that my header is cracked (pretty bad) and I havent had a chance to weld it yet. I say that based on the thread I searched under heat soaked.

 

[joe_peters]

If it sputters when you try to start it, do a search for heat soak. There was a TSB on this, but you can fix it yourself easily. If you need some aluminized wrap, shoot me a PM and I have a huge roll I can cut you some off of and mail it to you.

If there is no spark at all, witnessed by pulling a plug and laying it against the block, then my bets would be on a CPS or a bad coil.

The TSB on heat soak covers 99-04 4.0 engines. The heat soak condition is the culmination of a series of design changes--elimination of the fuel return line from the fuel rail and relocation of the FPR to the tank area, the change of the manifolds in 99, and for the worst of the afflicted the 50-state emissions package with the two mini-CATs in the exhaust header, however the TSB covers both 49 and 50 state emissions vehicles.

The OP has given us a large clue--belatedly--his busted exhaust is probably contributing greatly to a thermal failure of the crank sensor.

 

[96TNXJ]

Thats what I was thinkin if I weld it up you think it will stop (assuming thats the problem) or with the CPS still be bad?

 

[joe_peters]

Yeah, if it is thermal failure the damage is done.

Welding the exhaust won't hold for long, so plan on a replacement soon.

Good luck.

 

[96TNXJ]

Yeah, if it is thermal failure the damage is done.

Thats what I was afraid of :hang:

 

[Portuga_XJ]

check your fuel pressure.

my jeep for about 1-1/2 years, i went crazy looking for what was wrong with the jeep. replaced a bunch of sensors and still, it would run, and when it would warm up, if i shut it off for like 5 mins and started back up. it would sputter, bog down, sometimes even shut off and not start again for a good 20 mins.

i checked the fuel pressure a couple weeks ago and it was at 28 psi.

sure enough, i changed the fuel pump and filter, and it runs like a dream now.

 

[96TNXJ]

Update:

Last night I was wheelin the xj and I knew if I cut it off it would take a little bit to start so I left it running. Well as I was driving the jeep just died and after letting it sit for a bit it fired right up. I checked air, fuel, and spark (when I was checking the spark is when it started) so I think its the coil pack. Ill look more so into that when I get the header welded up

 

[89xj]

put a heat shield around the coil and get the cps wiring as far away from the header as possible. i would pick up a couple of junk yard coils. cheap and carry one as a spare. i would also get a spare cps.

you need to test both the coil and cps when the engine is hot and having the no start issue

 

[96TNXJ]

ok this maybe stupid but how do I test the coil and the CPS?