Hey guys I'm new to the forum and having an issue with my Cherokee. It's a 96 4.0L HO. It won't start when it gets warm. I've been poking around and searching for a while and haven't found anything really concrete so any help would be great. There are no engine codes or lights on the dash. When it gets too warm it will turn over just fine but won't fire. Coil is working and it has fuel pressure, and it will occasionally cough like its trying to start but then go back to cranking. Any ideas?

 

Your sure your geting spark and gas and air?

 

New plugs, wires, cap and rotor. Coil is firing just fine and ohm tested just fine. It's got fuel pressure at the rail. I've been told to check and see if ether will start it so ill be.doing that later.

 

Pull a plug and check spark that way

 

I'll pull it in the garage and check it tonight if I can make it act up again. It's starts are getting slower and slower over the last few days but only when its really warm does it not start at all.

 

So odd I don't have the answer...

 

^^

Next time it acts up, grab one of those old plugs you yanked, attach a plug wire to it, ground the shell and crank. See if you get spark *when it's acting up*.
Coils are good for working just fine on the bench and measuring A-OK, but acting up once they get a little warm. Substitution is the best test.
I've also seen CPS' do that, but not nearly as frequently as the coil.

Also you might pull a plug after the no-start and see if it's wet with gas. If it's bone-dry, look into the fuel system.

 

I agree with the others. You must check for spark when symptomatic. You need a strong, BLUE, snapping spark to start the engine. Orange/white/yellow indicates a weak spark which may not be strong enough to start the engine.

If you have good spark, suspect a fuel problem. If you have weak spark, suspect the ignition coil. And if you have no spark, suspect the crankshaft position sensor or coil. It is not unusual to see thermal (heat related) failure on the crankshaft position sensor.

 

I’m having the same problem with my jeep that starts with starting fluid and I checked the spark from the coil to distributor and it’s not consistent replace the coil with a new one same problem