I picked up a ZJ to flip originally. My girlfriend has been driving it. The problem with the jeep is that it will randomly stall, typically at an idle or coming to a stop. Most of the time it starts right back up, but other times it wants to sputter and act stupid, sometimes it doesn't want to start. I was able to catch it doing it a little bit tonight. Fuel pressure is within range. I hooked up my scanner and recorded some live data. I have noticed that the auto-shutdown has turned to "yes" during these times that it stalls. What is the rule of thumb for this? CPS, CKP, cap, rotor, plugs, wires were all changed before me in an attempt to fix this issue. I'm wondering if it is in the ECM or if this is something else. I'm not sure, but I don't believe the "auto-shutdown" should ever say yes unless the key is off but I don't know that for certain. Any help? I have a saved snap on log if that helps anyone?

 

I think it is possibly the PCM (computer). From everything I ever did read on Jeeps stalling out, for some reason the 1998 model year Grand Cherokee is the one having many PCM related stall outs. Even when they were much newer still many of these Jeeps were all having this problem.

I see it being written as a problem of the PCM itself having strange characteristics of their soldering joints or with how the connectors directly attach to the PCM.

Many times if you take a screwdriver and sort of mildly tap it all around on the case of the PCM it is possible to recreate the stalling in this way. If you grab hold of the PCM itself and mildly pull all around on it the Jeep may stall. Or, if you grab hold of each of the connectors attached to the PCM and pull them in and out, up and down, or from side to side the Jeep may stall. Some people have solved the PCM problem by using zip-ties to hold pressure on the PCM connections in certain specific ways. Other people fixed the PCM stalling the Jeep issues by adding pressure to the backside of the PCM with a wooden shim of sorts being placed behind it, and in between the firewall. Still others were able to fix the same type of issues by removing the screws which are holding the PCM together and replacing them with other screws that were just a little bit shorter in length.

Most people reported taking electrical parts cleaner to the PCM connector pins and terminals to clean those up real good too.

 

I had a similar issue that turned out to be the pcm.

 

I had pulled the 2 screws out of the front and they had already been cut off. I turned around and left them out and put silicone in the 2 holes. I had also switched the ASD relay around, and she hasn't had an issue with it dying on her since. I'd say if it happens again, I'm just going to pick up another PCM and see what happens. Thanks all!

 

sounds more like the cam sensor not being OE, or possibly the crank sensor.

 

I just read an article on "Just Ask", where a guy with my same 1997 ZJ (only his was 4wd) Limited, was experiencing the EXACT SAME issue I have been having with my own 97 ZJ limited. It will start up and run beautifully, for about 10 to 15 minutes (basically however long it takes for the engine to reach operating temperature), but as soon as it reaches operating temp, its like s*** goes haywire SOME DARN WHERE, and the Jeep starts bucking and shaking, and just acting all types of crazy AF! And I only ever pull ONE code. A P1391 "Intermittent loss of CMP or CKP". I can clear the code, and reset the PCM, and wait till it's cold and start it up again, and same thing. It runs like the most well maintained 4.0L engine I've ever owned (and I've owned 4), until it reaches operating temp, and as soon as that happens, things go crazy again. I have replaced every sensor on the Jeep, some of them twice. The Crankshaft position sensor is a NGK/NTK brand sensor, which I purchased after removing a duralast gold sensor, after being told that these Jeeps require the OEM exact part due to tolerances. Here lately, I have been considering whether or not it could be possible that I got my hands on a bad sensor with the NGK/NTK sensor that is installed currently. They are anything but cheap though, and this issue has kept me out of work for so many weeks now, that broke doesn't even begin to describe my financial situation accurately enough! And sensors are far from the only item which I have replaced on this Jeep. Originally, it broke down on me in the bottom of a local tunnel here in VA. After getting towed out of the tunnel, and unloading the Jeep at my house, it sat there for 6 to 8 months, because at the time, I just so happened to have another vehicle that I could drive. But the head gasket went in that car, and it wasn't worth fixing so I scraped it. I installed a new PCM in the Jeep, but only after installing the new crankshaft position sensor, and fuel pump 1st. Those didn't fix the crank, no start problem, so I bit the bullet, and purchased a new PCM, had it installed in in 10 mins (after cleaning all the terminal pins on the harnesses with some contact cleaner, and orifice cleaning brushes, and then applying some di-electric silicone grease... After which, I plugged in the 3 terminal connectors to the PCM, and zip tied them into place, in order to ensure they would not work themselves loose, and just like that! A few seconds of turning the key, and she started right on up, and was running like a champ! Until it reached operating temperature of course! That's when all this BS I'm dealing with currently began. And since then, I've replaced the distributor cap, rotor, the pickup coil (camshaft position sensor), the spark plugs and wires, the ignition coil, the up and down stream O2 sensors (NGK/NTK were not available, so I went with DENSO), and I went through and pulled all the original grounds, as well as all the positive battery terminal wires, and I replaced them all with red or black 4 awg brand new OFC copper wire, and I crimped tinned copper terminal ends to all of them, and then put weather proof heat shrink on all the crimped ends as well, to prevent future corrosion (those wires I made on my own, saved me a good little bit of money over going to any place like "JeepCables.com" or anything like that, and purchasing a grounding kit. And I also got some really nice quick connect battery terminal connections, which each have 4 additional screws/lugs designed to accomodate accessories like lights, or car audio, etc. They look really good, and really, I know they are overkill, but they offer peace of mind none the less. Since then, I have purchased a powered circuit tester, as well as new (actually ever so slightly used) terminal connections for the PCM, and I have got some Chrysler JTEC style terminal pins which are brand new coming (100 of them), as well as a terminal de-pinning tool set. I plan to de-pin the existing terminals, and remove all the existing terminal pins from each wire, one by one, until I have re-pinned every single wire with its newly crimped terminal pin into the three 32 pin terminals that plug into the PCM. (Oh, and I have also returned the PCM once as well, just to ensure it wasn't a bad remanufactured PCM I got a hold of... It wasn't. The PCM itself is in good shape, and is not the culprit behind this current problem.

Anyway, this guy in the article I ran across, just before coming here and begining this comment, was stating that he had a diagnostic tool made by Snap On, and while I don't think he really knew how to operate it quite as well as a professional might be able to do, still, he kept going on and on about how his would do the same thing, starting out cold, running great, and then go crazy 10 to 15 minutes in, after the engine got up to temp. He said that as he would keep an eye on either of the CMP or CKP sensors, they would do wonderfully, until the engine got warm, and then the crankshaft position sensor would start throwing off these crazy readings that did not make any sense, and the diagnostic tool would state that the two sensors were no longer in sync. The last comment he posted, was in regard to the fact that he too had purchased TWO new sensors already, and that the one currently in use, was an NGK/NTK sensor, and he couldn't imagine BOTH being bad, but that he was ready to go and drop the money on a new replacement, just on the off chance it might resolve the problem. I feel like the fact that he had been going back and forth with the technician he had been chatting back and forth with, for over two weeks, but that suddenly, following his comments about the sensors going crazy, and being ready to purchase a new sensor (CKP) and try it out, is indicative of the fact that he all too likely, finally hit the nail on the head. I cannot even fathom the insanity of just how many bad parts I have purchased and received for this Jeep since I began trying to resolve this problem. There has been a bad fuel pump I had to return for a replacement, as well as a CKP sensor, an O2 sensor, a TPS, and I also replaced the original Duralast cheap-o dist cap and rotor set I purchased, for a much more heavy duty, and more quality looking setup made by ACCEL, which included a dist cap and rotor with brass contacts, as wel as wires with much better build than the cheap-o ones that I had previously purchased from Auto-Zone. I mean, I have had to return more parts for a replacement, because they didn't work, or just re-purchase a part due to the fact that it was not the right brand (they realy should not be able to advertise that so many other brands are a "perfect fit" for these model year Jeps, i fthey are so wel known not to function properly, or, to cause the Jep to not function properly, or at all for that matter, depending on just which part we might be talking about)

This whole thign is just crazy AF, and I canot believe that I am about to do it, but I am going out to remove my NGK/NTK crankshaft position sensor right now, and I'm going to take it back to Advance, and swap it out for a new one. I canot believe that this could actualy be what my problem is, and while I will be happy if it resolves the isue, at the same time, I will be livid at how much unecesary money I have spent on this vehicle at the very same time! Anybody reading this, kep your fingers crosed for me. Oh, and as it happens, my PC is mesing up now too, which is why all the mispelled words!

 

Just FYI, for anybody coming to read this in the future... Changing the CPS DID in fact resolve this issue! It wasn't just that simple though. The CPS I received this time - a replacement under 3 yr limited lifetime warranty from Advance - came with some very valuable literature, which explained that it is necessary to first ensure that you apply pressure to the back end of the CPS as you install it. Meaning, once you get it into it's hole in the bell housing (after sticking your finger in there to be sure you feel a solid, flat section of the part that spins in front of the tip of the sensor first), when you are tightening up the retaining bolt that holds the CPS into place, you must also apply continuous pressure to the a** end of the CPS as you are tightening the retaining bolt up. This ensures that the cardboard spacer stays pressed tight to the part it is supposed to meet up with inside the bell housing. If installed properly, the cardboard spacer will be immediately torn away upon starting and/or moving the vehicle, which means that the CPS is now properly spaced from the part it senses. Only then can the CPS function properly. If it is not installed properly, the vehicle WILL run ALL F'd up once it hits operating temperature.

I followed these directions when installing my most recently obtained NGK CPS, and my Jeep ran beautifully for a period of 2 weeks! Now I am dealing with a different problem, more like what is actually described in the first post in this thread. I'd love to hear from anyone in regard to just what it may have been that any of you did to resolve this problem. That is the single greatest issue with Forums... Folks turn to the forums when they are experiencing problems, but don't want to rely upon a mechanic. But then, after receiving a few suggestions, they typically never return to share with the rest of the individuals who they've been communicating with in a thread, to let everyone know which suggestion it was that wound up being the cure, or solution to their problem. If anyone knows what could be causing my 1997 ZJ 4.0L to want to stall at low RPMs, I would love to hear any suggestions!