Intermittent Stall/Failure to Start

I've got an intermittent stall-no restart issue. Jeep stalls and usually won't restart right away, but will restart a couple hours to a few hours later. I went at it the old-school method by checking for spark, fuel delivery, air flow, and no luck.

1995 XJ
4.0L
Auto Transmission/4WD

First problem was a stall at highway speed, and no restart; engine cranks but no fire. Towed it home and jumped in it the next day and still no fire. Swapped out the coil and it fired right up. Next day it stalled again, and no restart, but did restart after a couple hours. This goes on for a couple days.

Next plan of attack is to change the crankshaft position sensor. Stall reoccurs, but restarts after a couple hours.

Next effort is new distributor. Distributor was in bad shape when replaced, but stall reoccurs. Tried swapping ASD relay with A/C relay, but no restart, check current flow to #1 plug with timing light-no fire.

I then read about faulty grounds, so I cleaned all of the grounds, checked fuses, cleaned battery connections. Drove it around and it stalled, but would restart, so I'm thinking ignition problem is now gone, but maybe fuel delivery problem.

I check fuel pressure regulator and it tests ok, and I swap fuel filter but stall reoccurs. I swapped out the fuel pump, and test drove it and this time it stalls and no restart-back to dead ignition symptom.

In desperation I recall reading something about the mounting screws for the PCM, so I loosen them and the Jeep runs with no stalls. Not believing that's a real solution, I went to the salvage yard the next day and grabbed a PCM and used fuel pump and ASD relays; I swapped the PCM and relays out and drove it for over an hour with no issues. Kid drove it around during the weekend-no problems.

Kid drives it to school Monday and it stalls again, but restarts. Tuesday the kid drives it to school and it dies before she can get out of the subdivision-no restart.

Pushed it into the garage last night where it now sits. I'm at a loss as to where to look next.

In summary:
New distributor
New Crankshaft Position Sensor
New Coil
New fuel filter
New Fuel Pump
Fuel regulator tests ok
Cleaned Idle Air Control Module
Inspected Throttle Position Sensor
Swapped ASD and Fuel Pump Relays w/salvage relays
Swapped PCM
Cleaned grounds at PDC, battery terminals, and power supply to PDC

Anybody have an idea what else to look for? I've combed through this forum, but haven't really found discussions about problems quite like this.

Could be something simple like O2 wire shorting, or key cylinder shorting, or who knows what.

Get a stethoscope and listen to the injectors if they are clicking when you have the no-spark. If so then its an ignition problem. Otherwise its probably on the control circuit--crank sensor, cam sensor, ASD relay, computer, or one of the wires.

Thanks for the reply EHall.

I gave a quick look at the O2 sensor wiring and didn't see where it looked like anything was in contact with it.

Key ignition switch was recently replaced (by Others); I'll check to see if maybe they pinched a wire on the reinstall.

I'll check the injectors operation.

If it isn't the normal stuff it is likely to be the abnormal. The dark green and orange wire going to the injectors and power for the coil is power *in*, both the coil and injectors trip or switch on the ground side. A likely place to check for power *in* is at this wire. A lot of splices on this circuit. This will also tell you if the ASD relay is closing or the 14 fuse is bad.

I've only seen it twice but I have seen a hairline crack through a fuse element that heated and cooled and worked just like a bi metal. You need good eyes to see a tiny crack in the fuse element. Either the 2 fuse or the 14 fuse.

Check for voltage at the orange wire going into the CPS (with the connector connected). I'm pretty sure it is supposed to be 8 volts on the 95, but this voltage does change year to year and I'm not certain. Low voltage here can cause unreliable CPS function. The low voltage is most often a shorted sensor on the same power supply, the cam position sensor or the speed sensor. Or maybe a wet, coolant soaked or corroded connector letting voltage go to ground.

Do you have an anti theft module in your 95? There is a dealer installed anti theft module that is sometimes integrated into your remote door lock circuit.

Just a few unlikely ideas.

I've tried all sort of ways to voltage check circuits with the connector connected. Back pinning or one of those wire pricking clamps are both iffy. I don't screw around anymore, I strip back a little insulation on the wire I want to test, just on one side of the wire with an exacto knife, so I'm sure I'm getting good contact with my test leads. If you keep it small, a little dab of silicon will seal the insulation back up again quick.

Got home after work and no-start, which is good, I think, because I can't chase the problem when it starts.

Tonight I couldn't dive too deep into it, but I unplugged and tested for voltage at the IAC, TPS, CPS, Engine Temp, Intake Temp, and MAP sensors. Had solid voltage at all of them.

I also put my test light on the fuses and all had voltage on each side of the fuse.

When I turn the key to the ON position, I hear the fuel pump run for about a second and a half, and the fuel pump relay click in.

Tomorrow I'm going to check for voltage at the Vehicle Speed Sensor on the transmission, then test all of the sensors individually. I think I'll also get some new micro fuses and swap them out just in case 8Mud is onto something about the cracked fuse.

I know that you changed the CPS but that is the exactly what happens when a CPS goes bad. Is it possible that you got a bad one?

Started in on it this morning and it started up, typical, so can't test sensors as they'll all test ok when it starts and runs. The only thing to do is take it out for a drive until it fails, but then it's a bugger to get it back in the garage so I can work on it.

8Mud, I pulled the fuses and inspected them with a magnifying glass, and all looked good.

Update - Drove the dang thing for almost an hour this afternoon and no stall. This is maddening.

I'm about ready to trade this thing for an accordion; I've always wanted to learn the accordion.