Hi, We have a 96 Cherokee sport with a 4.0 HO. It randomly stops running. Give it a little time and it will start back up. It had a bad crank bearing and a bad ring so we decided to replace the short block and clean up the head, new lifters and pushrods, etc.... We hoped in the process we would find the problem. The distributer shaft had a lot of play, we replaced it, so the cam sensor was replaced because it's inside. After getting everything back together it wouldn't start. We looked at a lot of these forums and kept finding that the Crank sensor could be bad so we replaced it. It started right up fine. After a half an hour or so it stalled and wouldn't start just like the original problem before the rebuild. We used a code reader on it and it said "PO340 mod$D1 Camshaft position sensor". When it doesn't start there is no spark and the fuel injectors aren't spraying. With the cam and crank sensors new, What's left?

If anyone has any ideas we would really appreciate it, we're stumped. Thanks.

 

I would try the ignition coil. When they go bad, usally happens just after motor gets to temp. The temp causes the weak coil to break down.

 

Thanks,
That sounds right for the no spark but the fuel injectors also don't work when it's not starting. To me that would mean whatever triggers the injectors and coil.
I have a Oscilloscope and Multi-Meter, I wonder If I can test that.

 

You may have two problems. Fuel pump and coil.

 

When It dies there is still fuel pressure in the rail?

 

Fuel yes but the pressure will quickly drop.

 

I had a problem like that in my 90 when I was 1st getting it on the road. The middle wire on the coil connector was burnt up inside the connector. Sometimes at low rpm's it would get enough connection to run the engine but then it would quit. It was a tough one to find because it was up inside the connector and hard to see.
clint

 

Thanks,
Just checked the coil wires/connectors and they're fine. The coil only has two wires on mine, plus the spark wire on the other side.

 

get a new coil it's $30 and you can be sure it's not the problem and will be good for 50K+.

 

This may sound crazy but I found a post from a guy who had the same problem. He resoldered all the solder joints in the ECU and recrimped all the connector pins and still had the same problem. In the process one time he did not tighten the mount bolts for the ECU all the way down and his ran perfectly. I loosened the 4 mount bolts on ours and it been running fine ever since. Go Figure. Probably a bad connection in there somewhere and tightening it down forces an open circuit.

 

I have a 96 Cherokee and I just replaced the clutch, pressure plate, flywheel, throwout bearing, etc. Interesting thing is that when I pulled the transmission, it was missing three bolts that bolt it to the block. I replaced them, put it all back together and went to start it. Nothing. It cranked, but it never started. I tried doing a rolling start, the thought process being that if I had a stuck starter pinion, that would make it start. Nothing. I thought it was the fuel pump, so I pressed on the fuel pressure release valve on the fuel rail, ran the starter for 5 or so seconds, and checked it again. Fuel pressure was fine, so pump is out of the question. One thing I thought of was that I had the engine transmission combination lowered quite a bit upon reinstallation. Maybe something went wrong there. I started looking around and found a couple of unconnected harnesses, neither of which had corresponding connectors. Tomorrow, I'm going to check for a spark on my plugs and put a voltimeter to my injectors. I bought a new rotor and cap, was going to buy a new coil and maybe a distributor. I don't know. We'll see what works.

 

A bad coil will not effect the fuel injectors and keep them from spraying. Check all of your connections and grounds. STOP REPLACING IGNITION COILS BLINDLY! Do some diagnostics before throwing parts at it. Do you have voltage to the coil? Is the ground side of the coil pulsing? What is the resistance on the primary side and secondary side of the coil?

 

After a month or so this problem came back. Occasionally the Jeep just stops running. wait 5-10 minutes and it will start right up. It will then run fine. A week or so later it will just randomly shut down again. Wait 5-10 minutes and it runs fine again. We broke down and bought a new ECC (Brain)($250). It did the same thing today.
As a recap, we replaced cam sensor, crank sensor, ECU, engine, distributer, etc...
This is nuts. Any ideas out there?

Jeff D.

 

Fuel Pump Relay, Check the Ignition Pickup, Cam and Crankshaft Sensors. I had a similar problem with an old Jeep I had and ended up selling it.

 

Did not check the fuel pump relay, but the injector rail holds pressure good.

Again I replaced the cam sensor, crank sensor and complete distributer, including cap router wires and plugs.

Thanks