justin13703

A friend of mine recently bought a 95 Grand Cherokee Laredo, 4.0L, automatic trans. Recently it has been having issues randomly shutting off and then not starting back up until it damn well feels like it. Then for the most part runs great until it feels like shutting off again.

So anyway, there are no codes. When it shuts off, it's like you flipped the key off, it doesn't slowly die or stall, it literally just turns off. All the rest of the electrical stays on. Sometimes it will fire right back up first try like nothing ever happened. Sometimes you can crank till the battery dies and it won't even try to start. It is completely random when it shuts off, it will do it idling, coming to a stop, accelerating, or just cruising down the highway. It seems to be completely random. It will also buck while driving sometimes before it shuts off, kind of like a hard misfire or something.

So here's what has been done. New oem Mopar crankshaft position sensor installed. This made no change. New coil installed. This made no change. Injectors were checked to see if they were getting signal, they all were. Spark plugs are all getting spark. Fuel pressure is at right around 40psi. I am lost at this point because when mine had these same issues it turned out to be the crank sensor and apparently this isn't the case here.

A bit of interesting info, the cam sensor, if unplugged, would still allow the engine to start and run fine, and throw no check engine codes. But it would still randomly shut off. With it plugged back in it is the same result.

Sorry about the long post

dave1123

I don't understand why it runs with the cam sensor unplugged. That boggles the mind. As far as randomly shutting down, it could be the PCM heating up and a bad solder connection opening up. One poster in Arizona had to put ice on it and then it would start right up. Another had to warm it with a hair dryer before it would make connection. In other words, I suspect the PCM is at fault.

justin13703

Really that's crazy, it's weird though cause most of the time as soon as it shuts off you can pop it in neutral and it'll fire right back up, before it even comes to a stop. It does it sometimes when it's ice cold and sometimes when it's been driven for hours. It's really weird

Fire_Busch92

Did you check the Neutral Saftey Switch. There is a thread on here for removal, disassembly, cleaning and adjustment.

Fire_Busch92

I lied its not on here other site but try this http://www.bc4x4.com/tech/2010/jeep-...ty-switch-nss/

Bustedback

The Grand Cherokee has a different NSS, nothing to take apart and clean, just replace a 10 dollar switch. I think it's a crank sensor issue, or a failing cam sensor.

justin13703

Would the nss cause the jeep to shut off when running though? I know it can cause it to not start but I don't believe it will make it shut off out of nowhere

justin13703

The crank sensor was just replaced with a new mopar one about 3 weeks ago and it made no change. And the thing will run the same with or without the cam sensor even plugged in, which makes no sense to me. I'm leaning toward his problem being in the computer itself

Bustedback

No, the NSS won't cause the engine to stall. You just might have an ECM problem.

justin13703

Ok that's what I'm leaning towards. Do you know what could be up with the cam sensor though? Like I said we can leave it unplugged and it will still start and drive around fine but still will randomly turn off. No check engine light either. So it's almost like it's not doing anything at all

Mugz

Might want to try camshaft sensor. Mine was doing same thing I replaced crank and cam sensor. She rolling.

justin13703

Ok well a little update. We put a new camshaft sensor in it. No change. We put a new computer in it. No change. Lol

So far, as far as I know, here are all the parts that have been replaced on this thing:

ECU
Crankshaft position sensor
Camshaft position sensor
Distributor cap and rotor
Spark plugs
Tps
Coil
ASD relay
Iat sensor removed and cleaned
Grounds removed and cleaned
Fuel pressure verified at around 35psi
Each injector checked for pulse, they were all getting signal

I'm freakin clueless as to what is causing this. I guess about the only thing left is faulty wiring somewhere. Which is strange because it all looks in perfect condition. Actually the whole engine on this thing looks like perfect condition. It's the cleanest jeep engine bay I've ever seen.

dave1123

Just throwing this out there for jollies. Check the MAP sensor hose for cracks. Likewise, the CCV.

justin13703

Ok I'll have him check the map sensor. The CCV fittings and lines are good though, I remember when I looked under the hood that was the first thing I noticed since most all 4.0 CCV fittings are all cracked up lol

KE6LUK

My 1996 did the same thing and it just about drove me nuts. I replaced everything that you have. It wasn't until a neighbor hit my new ECM while I was cranking the engine that it fired right up. With a little more checking the new computer was bad at the connectors.
So my suggestion is to wiggle the connectors up and down to see if they make the vehicle shut off.
Hope this helps.
Doc