My '99 Grand Cherokee, 4.0 inline six will shut off on me while driving. It will start right back up, it used to only happen about once a week but now it's doing it 2 or 3 times a trip while going to and from work ( only a 10 minute drive). Any ideas on what would cause this? I'd like to fix it before it leaves me stranded. It's not throwing any codes. Thanks

I had the same problem with my 98 GCL. turned out it was the ECM computer. Of course it's dealer only and needs to be programmed with correct software and your VIN. It's about 350.00. I'm not saying this IS your problem but they are known to malfunction. Mines been fine ever since.

Pull the ECM but leave the wires attached. Start the vehicle and let it warm up. Tap the ECM several different places on the case with a plastic screwdriver handle. If it shuts off when you tap it, you found the problem without spending money for a diagnostic fee.

on my 04 I tried all the stuff mentioned above, then i took it to the dealer and turned out to be the batt, dealer didnt charge either..

When's the last time you cleaned the throttle body??

I just bought the Jeep last Fall. I've never cleaned the throttle body. Is there a certain frequency these should be cleaned?

I'd say "now" is probably a fantastic time to do it. Unless you're running rough, stalling, poor idle, rough starts, there's really no need to do it. Although maybe I overkill, I do it like every 3 years roughly. Its a 98 and I've owned it 8 years, 150K on it. I was having all the aforementioned issues and was leaning towards a bad / clogged injector(s). Turned out to be a nice carbon buildup in the body. Just a suggestion as I've been down this road with your symptons.

I've heard the crank sensors are a common problem on these engines. Do you think it would act like this or would it just shut off and not re-start?

Are there any stored codes in the PCM? There is usually a counter that tells you when the codes were last cleared. If it says 0 or 1 start since cleared and there are no codes, you may need a PCM. I have seen a bad PCM act like this, it would never store codes and always said 0 or 1 start since cleared. If there is a bad sensor it should store a code especially with the consistancy it is happening at. You have to start with checking codes.

When you do get to the bottom of this issue, plz advise the culprit. Thanks

My 00 Cherokee cut out intermittently.

I put in a "rebuilt' ECM off ebay. Problem solved.

You can try your luck with other boneyard ecm's if you can find them cheap enough.

The only real advantage to buying a supposed rebuilt is that they reflash them with the highest level code and may have a warranty.

Tom
Same thing happened to me with my 89 Grand Cherokee. Had to go for a new ECM. Got it from a auto part store in flushing and had the Mobil do the install and programing was a while ago though.

I tried to pull codes by with the key method and discovered you can't do that with a '99, '98 Jeep you could. Drove to Advance Auto where they used a scan tool, NO CODES. The way I figure a sensor would throw a code, if the ECU was going bad there might not be a code because it stores the codes. Does this sound correct? I removed the air box, the throttle body looks spotless inside.

My folk's '94 had a similar issue. It'd just die going down the road, put it in neutral and it'd start right up. We swapped the sensor on the top of the bell housing. I think it was a crankshaft position sensor. Funny thing was we 'found' another old sensor that was up there hanging on by the wire harness clip. So it was not the first time...

That sensor looks like it's almost impossible to reach. How does anyone get their hands up in there to work? Does the front driveshaft need to come out?

The crank sensor should set an engine code. I think before you start throwing $100 parts at it you should just pay the dealer to hook up a DRB 3 and diagnose the problem. Auto Zone scanner will not do a fraction of the things you can do with a DRB.

Installed new crank sensor, seems to have fixed it, so far.

Been a week now and no more shutting off. I'd say it's fixed. Bad crank sensor. Thanks to all that helped.