Hello All,
To say the least, I have a problem with my son's 1996 XJ Country. We recently added a 3 inch Rough Country lift kit. After we finished up, took it for a ride and we gained a severe DW. I know we have a lot of work to do on the suspension, and the lift made it very apparent. I know well the whole list of items I need to check for on the DW. But first, the problem that we have to deal with is that it has the CEL and the GEN light, as well as no spark to the plugs. Just before I got the Jeep stopped the engine died and could not get it started again; had to tow it home. I used my handy-dandy spark checker from Harbor Freight. I swapped out the battery with a known good one from my 1991 XJ because all the shaking caused some of the electrolyte to spill out. I did get good fuel pressure at the rail. My initial reaction is that the PCM got shaken to death. I pulled it out, and the connectors are corrosion free. I have some electronics experience, so I intend to pull it apart to see what is going on inside. Now that you have the two-cent tour, what do you think? I have been lurking around here for a good long time, so I know of the vast experience that I am trying to draw from. Thanks for your time.

 

So a friend of mine had a similar issue, He replaced several things trouble shooting what was causing it to not get power to the PCM. turned out that while we where installing his T-case some how we shorted out this fuse/part from the battery to what ever it goes to making it so that he thought he had a bad PCM? Google this part bts103 (Napa) He also replaced the Throttle body sensor ec3313 but I'm pretty sure the battery sensor was the issue. From now on I will always disconnect the battery cable. when wrenching on it just as a precaution.

 

Thanks JandDGreens. I saw that sensor under the battery and wondered what it was for. My 1991 XJ does not have one. This Jeep was running normally before we parked it for the lift installation. It sat for about a week while we were getting things together. While my son was working it, he left the hood up with the light on for about a day and a half. Of coarse, the battery went low and would not start the Jeep. We gave the battery a jump and ran it for a while before he took it out and found the DW problem. It had no issues until the first good DW event.

 

While we are discussing the battery temp sensor, does anyone have an idea of what the ohmic value would be for the sensor at normal operating temp of the Jeep? One other thing that I forgot to mention is that prior to all of this madness, my Harbor Freight code reader has never been able to 'link' with this Jeep. That is why I am guessing at what may be causing the CEL and GEN lights. I have pulled and cleaned the grounds at the PCM.

 

The code scanner is probably ODB2, and the jeep is OBD1. You can use the key trick to read the codes. Turn the key off and on 3 times and count the check engine light flashes.

 

Thanks Geek. This jeep seems to have a random mix of pre-'96 and post-'96 wonderfulness... JandDGreens, my son swapped out the battery temp sensor with one he pulled from my 1998 XJ, no joy. We will try the key jiggle to try reading the codes.

 

Geek, the jeep is not responding to the key jiggle...

 

there is a video on how to do the key dance.. maybe it will help you



marc

 

I would put that waaay down your list of things to do. The chances of it getting shaken apart are slim to none. The components are buried in a thick translucent silicone gel, which can't be removed with any common solvent. (No, not acetone, and not even MEK.) It takes some seriously dangerous industrial solvent to dissolve it. I don't recall the name, but it's pretty hard to come by, because it's seriously dangerous.

The usual death mode for them is a failed cap. They have some electrolytics in there, so opening up might let you see a bad one (swollen, split, or leaking), but other than that, you are not likely to learn anything. If something shorted, you might see a burned trace.

In the highly unlikely event it turns out the be the PCM, fixing it is not realistic. Just buy a new one.

Verify spark (or the absence thereof) and fuel pressure. Also check for 12 into the coil. The spark is generated when the PCM provides ground - the 12v should be constant when the key is on. Same to the injectors. Wouldn't hurt to verify 12v there, too.


Also check yoru battery cables. All four. Yes, four. B+ to the PDC and to the starter. B- to the block and to the inner fender wall. The PCM grounds on the same plate as the B- to the block. Get rough - yank pull push. You are trying to expose any hidden problems. If it's corroded and barely holding on, you want to break it so you know to fix it.

Also investigate your ASD relay. It controls spark, injectors, and fuel pump.

 

LadyKenai, we got the key dance to work. Unfortunately, the jeep gave us 12-55. In other words...nada. BlueRidgeMark, I will not be opening up the PCM. All the fuses have power on both sides on both panels. Last year I made all new cables and the grounds are all in good shape. There is good fuel pressure at the rail, but no spark. Gave the battery a good charge. Currently, when the engine cranks the CEL is on. The GEN light goes out after a few cranks, but the engine does not start. We will be checking out the coil today. Something of note, as the engine is cranking the distributor has a slow wobble to it. This is with the cap on. I took the cap off to check it out and the rotor is solid and undamaged.

 

Could be your cam sensor. If the distributor bearing (bushing?) is shot, it can wipe out the cam sensor. It's under the rotor.

 

BlueRidgeMark, as the engine cranks I can smell fuel. I understand that the CMP is involved in fuel injection and dwell. Would this indicate that the CMP is working and allowing the injectors to function? I have replaced the distributor on my '91 that fixed an intermittent shutdown problem. I believe the CMP was bad on that one.

 

That would be my guess if it is not the Battery sensor. Mark's 96 has that cam sensor or what ever it's called go out once in a while.

 

Good question. I just looked it up in my 97 FSM. Here's what it says:

So, no influence on the spark. Fuel only. You know you are getting fuel, so that suggests the sensor is operating. But that leaves the question, is it operating correctly? It's a pretty simple device, and I can only think of two things that could be wrong with it:

1. It's dead, Jim. Nothing. No output. I don't think you'd get fuel into the engine at all.
2. Timing is somehow off. Yes, you get fuel, but at the wrong time.

#2 is interesting. I was driving a borrowed 62 Falcon one time, and it suddenly overheated. Turned out to be due to severely retarded timing. The rotor had broken in such a way that the metal tip was pushed backwards.

I'm just wondering if something like that could be going on. Can't hurt to pop the top off the distributor and take a look.

 

First would be to check the ASD fuse in the PDC (under hood fuse box). If there is no voltage on that fuse, my first thought would go to the CPS having been damaged during the shaking (connectors, harness, or the sensor itself). If I -did- find voltage on that fuse, I would follow it down and see if it was getting to the coil. If I found it going into the coil, but not coming out the other side, I would turn my attention to the possibility that the coil was somehow damaged by the shaking. (heat and vibration are the things that coils and CPS sensors don't get a long with).

I have a scope, so if I suspect the CPS, I would use my scope to see if it had an appropriate signal coming out of it. Without a scope, it can be difficult to troubleshoot definitively. Sometimes for DIY, the easiest thing is to swap it with a known-good part. Also, CPS sensor needs to ride very close to the fly wheel to measure it, so violent shaking of the motor could possibly knock it out of position just slightly, and if it was already on the edge, that could push it over.

These things aren't for-sure but they are what I would suspect first.