96 XJ 4.0. This problem only shows up when the outside temps get hot. The engine temp is not over heating. After it has been sitting for a while and the engine is cool it will start and run fine. After driving it and getting it up to operating temp and cut it off to go in store for a minute when I come back it will not start. I believe it is a temperature issue. Something is getting hot not allowing me to start the engine until is cools back down. Once it cools down enough i can start it and drive it as long as i want with no problems. Another senario, if I am sitting idle in traffic and it's hot outside it will start idling badly and try to cut off on me. If i can get it moving and cool things down a little it will start running fine again. It's consistent with this problem. These real hot days it has been doing this.
If the outside temps are cooler it will not give any problems/?? Any ideas???
Thanks.

 

I would replace the battery positive and negative cables first, with something of good quality and the heaviest wire gauge you can get.

NAPA sells some that seem to be pretty good.

When you install the new ones, make sure all connections are clean and tight.

 

One other thing that may be helpful. The engine has to spin over a couple seconds before it will start. ?? This is every time.

 

That doesn't sound particularly abnormal.

 

For this, try the poor mans prime. Before starting. Turn the key to power up the fuel pump don not start it. do this 2 or 3 time then try to start it. If it start faster then you may have a bad anti-flow back valve on the fuel system.

 

Crankshaft Position Sensor, same thing would happen to me. After it would get warm and I shut it off it would take about 20-30 minutes to cool before I could restart it. When you try to restart it does it just crank and crank and crank with no ignition? If so, replace the CPS. It is cheap and easy.

Sometimes while driving, mine would cut off when I approach a stop light and then it wouldn't restart for another 20-30 minutes. I also adjusted my TV (kickdown) cable which helped with the idle.

 

The possibility of predetonation is possible. Commonly called heat soak, it's where your injectors get hot enough to atomize the fuel before it reaches the cylinder. The symptoms are just what you described. If cooling system is up to snuff- good tstat, water pump, radiator and lines, then consider adding a little heat shield around injectors and/or hood vents. Best bet is to fix problem and not have to add aftermarket stuff to bandaid it, though..

 

I would start with the CPS seeing as how its outside temps that you are noticing causing the issue. The hotter it is outside the longer it takes for everything to cool back down. When its cool outside it takes a lot less time so you probably haven't noticed it until it got hot out. Outside temps shouldn't be an issue with predetonation.

 

I put code reader on it last night and there were no codes. I was wondering about vapor locking or something to that nature. I'm going to run it tomorrow until it starts acting up and spray the fuel rail with some
sensor cleaner which should cool it down and may be able to narrow down
where the issue is. Thanks for some good places to start. I'll update ASAP.

 

Next time it won't start after you turn it off, pour water on the fuel rail and injectors and see if it starts then. If it does start then it's what VTJeep is saying with heat soak.

 

I agree with Epk5150. I had simular issues. Replaced the crank position sensor with a good one from dealer. No further trouble.

 

Same here

 

I installed a CPS sensor. Not sure that fixed the problem. It cranked up fine but it sit and sputtered a little at first then smoothed out. It hasn't been hot last couple of days. So, i can't tell if it fixed the problem with the heat. I drove it this morning and at first it had a dead spot about 1/4 of the way into the gas pedal and then would smooth on out and finally it didn't do that any more once it warmed up?? Not sure it the computer reset or? Will update as soon as i drive it a little.

 

CPS did NOT fix the not starting when hot. Will continue

 

Where is the fuel check valve that keeps the fuel from draining back into tank when motor is off?? Is it in the fuel pump? Thanks.