Lamp Outage Module (LOM) & vibration in engine(like a miss)

[msdz]

I have purchased a used '94 JGC with 161,000 miles on it. The jeep is in excellent condition besides a few minor flaws. It does not smoke, leak or anything I would have expected from a vehicle with this amount of miles on it.

Now to my problems, I have seen a few other threads reguarding this matter but none have helped me out yet so I am asking again for some suggestions.

I have the message "rear lamp failure" popping up on my vehicle information center (VIC). I have checked all my wiring and all my lights. I replaced all my lights with the specified bulbs just to be 100% sure that is not the problem, I seen where someone wrote the high mount brake light has 3 bulbs to be replaced, not on my '94 model it does not, just 2, double checked and DEFINITELY just 2. I replaced the LOM with a brand new one with still no help. I checked the voltage at the LOM and all is as it should be. What I am figuring can be wrong is there is a possible short somewhere from the LOM to one of the lights, although they all work as they should or even to the trailer electrical connector. Any ideas of how to go about doing other test or problems would be greatly welcomed. Oh, the only time the message appears is after I hit my brake pedal, I can sit still or even drop it in gear as long as I do not touch the brake pedal this message does not appear. As soon as I hit the pedal it beeps and gives me the "rear lamp failure" message. I had thought also the brake switch on the pedal had some problems to cause the message to appear. Trying to figure out how to check it with a multimeter, any instructions on this would be nice as well.

Now the other problem I have is after starting my JGC it has a vibration that seems to be coming from the engine, does it while idling or at highway speeds. The only time I do not notice this is when I am "getting on it", like holding it to the floor when I am passing somebody and under strain. It does still have the vibration when sitting still and rev'ing the engine up to about 4,000 RPM's. I have checked my plugs and all looks great, no oil fouling or any other signs of the plugs not firing. Only idea that came across my mind was that maybe one of the injectors is clogged or dirty.
I was told that the fuel pump not putting enough pressure out could cause this also but it runs to good for that to be the issue, no hesitation or any other signs of fuel being the problem. I do have to let the pump build up pressure before starting though. I think that it is leaking off when it is sitting for any amount of time for that to happen. My jeep is getting about 21 MPG on the highway and has the 5.2L and full-time four wheel drive transfer case, with it getting this MPG I do not think it is something really major just want it fixed and running properly.
The only thing I have had to do to this jeep since buying it about 2 months ago was replace the timing cover gasket when it started leaking anti-freeze, besides these issues it is by far the best vehicle I have had in a long time.

Other ideas would be welcomed on this also.

Sorry for the book but thought I would give as much details as possible.

[sreilly77]

Originally Posted by msdz

I have purchased a used '94 JGC with 161,000 miles on it. The jeep is in excellent condition besides a few minor flaws. It does not smoke, leak or anything I would have expected from a vehicle with this amount of miles on it.

Now to my problems, I have seen a few other threads reguarding this matter but none have helped me out yet so I am asking again for some suggestions.

I have the message "rear lamp failure" popping up on my vehicle information center (VIC). I have checked all my wiring and all my lights. I replaced all my lights with the specified bulbs just to be 100% sure that is not the problem, I seen where someone wrote the high mount brake light has 3 bulbs to be replaced, not on my '94 model it does not, just 2, double checked and DEFINITELY just 2. I replaced the LOM with a brand new one with still no help. I checked the voltage at the LOM and all is as it should be. What I am figuring can be wrong is there is a possible short somewhere from the LOM to one of the lights, although they all work as they should or even to the trailer electrical connector. Any ideas of how to go about doing other test or problems would be greatly welcomed. Oh, the only time the message appears is after I hit my brake pedal, I can sit still or even drop it in gear as long as I do not touch the brake pedal this message does not appear. As soon as I hit the pedal it beeps and gives me the "rear lamp failure" message. I had thought also the brake switch on the pedal had some problems to cause the message to appear. Trying to figure out how to check it with a multimeter, any instructions on this would be nice as well.

Now the other problem I have is after starting my JGC it has a vibration that seems to be coming from the engine, does it while idling or at highway speeds. The only time I do not notice this is when I am "getting on it", like holding it to the floor when I am passing somebody and under strain. It does still have the vibration when sitting still and rev'ing the engine up to about 4,000 RPM's. I have checked my plugs and all looks great, no oil fouling or any other signs of the plugs not firing. Only idea that came across my mind was that maybe one of the injectors is clogged or dirty.
I was told that the fuel pump not putting enough pressure out could cause this also but it runs to good for that to be the issue, no hesitation or any other signs of fuel being the problem. I do have to let the pump build up pressure before starting though. I think that it is leaking off when it is sitting for any amount of time for that to happen. My jeep is getting about 21 MPG on the highway and has the 5.2L and full-time four wheel drive transfer case, with it getting this MPG I do not think it is something really major just want it fixed and running properly.
The only thing I have had to do to this jeep since buying it about 2 months ago was replace the timing cover gasket when it started leaking anti-freeze, besides these issues it is by far the best vehicle I have had in a long time.

Other ideas would be welcomed on this also.

Sorry for the book but thought I would give as much details as possible.

when you say vibration, is it a slight vibration or is it very loud and very harsh? i mean it is a 5.2L V8 you are going to get some vibration from the engine no matter what. but if it is violent or there is more vibration than normal, it could be bad motor mount(s).

[msdz]

It is very slight vibration, more than it should be though. I can barely feel it but know that it is a vibration that isn't normal, it actually makes me think there is a miss like a spark plug is not firing or bad plug wire. I will give a check on the motor mount though, never crossed my mind to check that, probably easier checking it rather than the fuel injectors.

Still trying to figure the "rear lamp failure" message though. Just curious, is it possible the VIC could be bad? I have had this problem since I bought the jeep, thought it was going to be easy to fix, was I ever wrong.

[msdz]

What was the real purpose the LOM was put on the Jeeps with the factory towing package? I was told and read that it was put on Jeeps with the factory towing package to warn the driver when the trailer lights were not operating correctly. Would be nice if the LOM could just be bypassed and not get the message on the VIC.

[On the Right]

Originally Posted by msdz

What was the real purpose the LOM was put on the Jeeps with the factory towing package? I was told and read that it was put on Jeeps with the factory towing package to warn the driver when the trailer lights were not operating correctly. Would be nice if the LOM could just be bypassed and not get the message on the VIC.

Had the same problem on mine. 94 GCL 4.0. Someone had put 912 bulbs in the third brake light. I replaced them with 911 bulbs and presto the warning light was gone.

[msdz]

Thing of it is, I did replace all the bulbs with the specified bulbs and the message still pops up. I did have one wrong bulb that was in the Jeep when I bought it, thinking that was the problem I replaced it and still get same message. Only thing I can think of is a short somewhere or possible bad VIC, maybe even a bad brake switch. All I have read never claim to have any issues with a bad brake switch though, since it only gives the message after I hit the brake pedal that is the reason for thinking the switch may be bad.
Guess I will try to replace it while sitting in the auto parts parking lot, can return it if that is not the problem.

Any ideas of how to check the wiring to find a short might be helpful. I did check for voltage at VIC and LOM as I read in another web site. It all looks good with the voltage, just need to know how to find a short using a multimeter, if it can be done.

[fredjacksonsan]

Tracing to find the short is the best option, IMO. Do you have a trailer connector at the back? I've heard of those getting fouled with dirt or water and causing issues.

21mpg in a 5.2 full time? That's crazy good mileage.

[msdz]

Yeah, I have a trailer connector. 21 MPG is good after reading some of these forums, that is highway milage though, around town here I get about 9-12 MPG. All depends on how heavy my foot gets and if I take my kids to the bus stop and let vehicle run to keep them warm. I also think that a V8 gets better gas milelage here in WV due to the fact the engine doesn't have to work as hard as the little engines to get up some of these hills at the highway speeds.
I worked for an auto auction driving vehicles to and from dealerships and found out what vehicles had better gas mileage and which engines did the best for a certain type of body style. I have yet to see a factory Ford 4 0r 6 cylinder get any deceit gas mileage, but take the same vehicle and put a V8 in it like the mustangs and they got almost twice the mileage. There were some that did get poorer gas milage though with a V8, think it all depends also on the gear ratio and/or tire size.

[fredjacksonsan]

I can see the benefit of a more powerful engine in the mountains. I've gotten through WV a few times and see mpg go from 21 in the flats to 16 or less.

[bringselpup]

My owners manual says 921 bulbs go in the center high mount stoplamp fixture!

[msdz]

I know, I replaced ALL bulbs just to be safe, still no help. The bulbs are definitely not the problem, it would almost have to be in the wiring. My main question is how should I go about checking the wires with a multimeter? Also could the brake pedal switch be part of my problem? All lights work fine, just getting anoid with the message in the VIC and the little beep that sounds when I first hit the brake pedal. That beep has scared the crap out of me thinking something was really wrong.

[bringselpup]

You can neuter the beep module so the thing won't drive you nuts. There are posts here on how to do it.

I would go back to those rear lamp assemblies and look them over good. Corrosion, frayed wiring, dirty lamp sockets.

Is it stock trailer wiring or aftermarket? If it's aftermarket maybe find a way to undo it for a bit and see if it's the cause.

[msdz]

Stock factory wiring harness. I have checked the sockets and wiring at the assemblies and all look good, that is why I think it is a short in wiring somewhere else or maybe the brake pedal switch.

[msdz]

Alright, I have another question for somebody to answer. Can the factory trailer wiring harness be disconnected and find out if that may be the problem? I looked and could not even see any wire connectors for it, must be hidden, possibly in bumper cover? I know I could disable the warning beep but that is not solving the problem though. I want it to be RIGHT and not spend a fortune taking it to the garage to let someone else fix it when I know I can do it if I track down where the problem is at.

[bringselpup]

I don't think my trailer wiring is stock, but it arrives in the rear compartment drivers side. Behind where most folks would have the spare tire. (if you weren't me and didn't carry it because I need the room)