TealThunder

Last night my xj left me stranded for the first time in my short tenure of owning it. For reference it's a 95 2 Dr with a 4.0, AX15, np231 with a sye and a 4.5" long arm kit and a whopping 304k miles. Was about 10 mins from home, cruising along just fine and motor just died, no check engine light or anything. Pulled over and tried to get it restarted and it was cranking strong but no fire. Fooled around with it for 10 mins and checked fuses, made sure there was fuel getting to the rail and checked all the plugs and what not were plugged in good, still couldn't get it running so I decided to call AAA for a tow. After sitting on the phone with them for 10-15 mins I decided to give it one last shot tor try and start it and to my surprise it fired right up. Turned around and headed back towards the house and after 2 or 3 mi it died again. Got it towed from there back to the house and when I got it off the flatbed it fired right up again and I was able to get it into the driveway. Any ideas what could cause something like this? It seems like it is heat related based on the fact that it fires right up cold but weirdly I drove it probably 45 mins round trip midday Saturday without issue. My dad was thinking maybe the ignition coil getting hot and not making a connection anymore, another friend said he'd have similar issues when the ECU on his zj was going bad, tow truck driver said he had a Wrangler that gave similar issues when the alternator went bad but battery is still holding strong so I don't think it's that.

Any ideas?

Very Red XJ

Leving, you stranded in often due to failure of the crank case position sensor - that's the first place I'd look

TealThunder

Bump. Any other ideas?

Very Red XJ

There's no easy way - get a shop manual. Assuming your air filter is clean, spark plugs, cap & rotor and wires are good, check for dangling wires grounding. Then open your shop manual and test your sensors: O2, idle solenoid, MAP and TPS. If they are good and your throttle body is clean move to the injectors.

The pins are for the wires

Testing restance in cleaned injectors
Fuel pressure at the rail,

tjwalker

Crankshaft position sensor is certainly high on the suspect list here. Any idea on how many miles are on the current one? This is one of the most common sensor failures on the 4.0 engine. When it fails, you will not have spark and you will not have fuel going to the injectors. The crank sensor can be tested (search) but know that testing is not always accurate and if the engine starts and runs when you test it, this sensor will almost assuredly test as good. If you do replace it, try to source a genuine Mopar sensor as aftermarket crank sensors are very "hit and miss" with a lot of miss. The crank sensor can suffer from thermal failure, I have seen it many times.

Probably the second most common thermal fail resulting in your symptom on the 4.0 is the ignition coil. The coil on your 95 can easily be tested for both primary and secondary resistances with a meter and a manual.

If you can idle it in your driveway and get it to fail, first thing to do is be prepared to test for spark. Remove a spark plug, keep it attached to the plug wire. Place the plug electrode near a good engine ground and have a buddy crank the engine over. You are looking for a strong, snapping BLUE spark. Orange/yellow in color indicates a weak spark which may lead you to a weak/failing ignition coil.

If spark is good when the engine dies and won't start, you need to test fuel pressure. If you don't have a fuel pressure gauge, they can often be rented inexpensively from a local parts store, call around for availability. Must be tested with a gauge as the devil is in the details with this test. For your 95 4.0 engine, you need approximately 31 psi to start the engine. Then remove the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. If there is raw fuel in that vacuum line, the fuel pressure regulator has a ruptured diaphragm and needs to be replaced.

As always, whenever symptomatic....it's a good time to review status of tuneup hardware. Often overlooked. Fresh Champion copper plugs gapped to .035, quality plug wires, distributor cap and rotor. Not likely the cause of a random failure like you are seeing, but if it needs tuneup hardware, it needs it and it is always money well spent.

Good luck and keep us updated!