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Electrical issues in my buddy's XJ

alex22

NAXJA Forum User
2001
4.0L
Automatic

When the key is turned to the run position from off the ASD relay, the AC clutch relay and the electric fan kick on and off until the key is turned off. It cycles about every 1-2 seconds. On some left turns the gauge cluster will loose signal and all gauges drop to 0 and the "check gauges" light will come on for a second or so. Not sure if the two issues are related. When it is turned on it runs fine, went from Fort Bragg to CT only stopping for gas without any issue.

When he got back from Afghanistan there was a mouse nest by the battery. He cleared out the nest, removed the fuse/relay box, checked and cleaned the wires and terminals under there. Battery is also new. Relays have been replaced and all fuses have been checked. He is currently running through whirring diagrams testing for shorts and bad components with Mitchell Online diagrams.

Any thoughts?

~Alex
 
PCM connector C3 pins 1, 2, and 3, are tied to the 3 relays that are cycling...so I would inspect the wiring starting at that point.

Thank's for the info, I'll pass it along.
Earlier he stripped the cover off of the loom headed from the PCM to the distribution block by the driver's feet and started shaking it. He narrowed it down to a loose connection in the distribution block, cleaned it, dielectric grease and the fan doesn't come in any more, just the ASD relay clicks so he's getting close.

-Alex
 
This is the unfortunate guy with the electrical problems. Intermittent problem is less intermittent, more permanent now. The fan, Ac comp clutch, etc, stay on for longer periods of time now. Went through the dist, block d/s kicker and there really aren't any issues there. Cleaned, poked prodded, wd-40, deialectric grease and a bad headache. Still haven't eliminated this as a sore point however seeing as it is the only place that has yielded even the slightest even if negative results. I checked those three pins going into the pcm, they have constant power. Issue doesn't arrive untill power is distributed through the pcm. Pcm has been replaced and determined not to be the problem. Checking all sensors and relays, just did the ac hi/lo pressure sensors, that is getting intermittent from the tan to 13 on pcm c3. With that sensor unhooked everything is still going batshit crazy. FML help
 
The PCM turns the ground circuit on and off for the relays to activate/deactivate.

So, if you focus on the the Electric Fan relay by itself, the only way that relay should activate and turn on the fan, would be the PCM completing the ground circuit for the relay by completeing the ground circuit thru PCM connector C3 pin 2 ( on a properly operating circuit). Same thing for the other relays with their respective circuit. Something is telling the PCM to activate these circuits. It almost sounds like there is a problem with the Ignition Sense circuit, or ignition switch circuit....possibly shorted to another circuit somehow causing it to cycle on and off. Maybe your blinker or Hazard circuit?
 
Tried messing with the blinkers and such, doesn't have anything to do with it. The cycling is too inconsistent for that to be it also, sometimes everything staying on for 30 seconds or more, or everything turning on and off in less than a second.
 
ALso may be unrelated but there is a power draw somewhere, causing the belt to squeel at startup. Interior lights will dim and surge with acceleration. I just redid the grounds at he battery, could be something else. Een though ive gone through everything on. I do have a pretty hardcore stereo in it with a 2 farad capacitor.
 
Check the low hanging fruit.....,

Namely the O2 sensor wires to see if one got snagged by the driveshaft, roadkill or the exhaust system, and check any other low end wiring!!!!

There is a large 12 volt wire to heaters in the O2 sensors, if they get grounded-damaged they cause some or all of the symptoms till a fuse blows.

Also check all the secondary grounds!!!

Have you checked the Alternator?

Lastly, it is possible the PCM is fried, but look for what fried it first!!!!
 
I was thinking along the same lines, i disconnected all 4 sensors, then did them in sequence upstream and downstream. No nuthin. I had the dealership install a new pcm and reflash. Still doing it. Threw an injector code for no reason, went through that. Determined it wasnt the pcm, returned it, got refunded 500$ hell yeah. Still not fixed.
 
Cleaned, pulled and poked the alternator ground. That also yielded no results other than fixing a small interior light surging problem at night. Next up... Great big truck alternator and ground upgrade. Probably just going to use some 3guage I have from sub and amp installs. I also have a 2 farad capacitor in this thing so there shouldnt be much for lack of power anywhere in the system. That thing is looped into the whole system.
 
Gonna toss alex's pcm in it tomorrow morning to see if the delaerships reman pcm was screwed up also. Mcque might be onto something with the ignition circuits. Looks like im ripping some stuff apart tomorrow. Might as well fix the loose connection to the back of my guages while I'm at it haha. On the bright side I get to drive it down to nc from ct towing a trailor in a couple days. The rubicon express 2 inch budget boost and roof rack look kind of snazzy no matter how much my wife thinks it was stupid to buy that stuff
 
Check the low hanging fruit.....,

Namely the O2 sensor wires to see if one got snagged by the driveshaft, roadkill or the exhaust system, and check any other low end wiring!!!!

There is a large 12 volt wire to heaters in the O2 sensors, if they get grounded-damaged they cause some or all of the symptoms till a fuse blows.

Also check all the secondary grounds!!!

Have you checked the Alternator?

Lastly, it is possible the PCM is fried, but look for what fried it first!!!!

What could have fried it... Well the mouse chewed grounds lighting on fire and sparking could have been it. Nice treat to come back from afghanistan to.
 
Check the low hanging fruit.....,

Namely the O2 sensor wires to see if one got snagged by the driveshaft, roadkill or the exhaust system, and check any other low end wiring!!!!

There is a large 12 volt wire to heaters in the O2 sensors, if they get grounded-damaged they cause some or all of the symptoms till a fuse blows.

Also check all the secondary grounds!!!

Have you checked the Alternator?

Lastly, it is possible the PCM is fried, but look for what fried it first!!!!

What could have fried it... Well the mouse chewed grounds lighting on fire and sparking could have been it. Nice treat to come back from afghanistan to.
 
Electrical problems are tough. Circuits that may be shorted together or poorly grounded are the worst. Sometimes isolating the circuit is the only way to find the problem. If you have the knowledge to check continuity of the wiring from point to point, and also check for shorts to power, ground, and adjacent circuit wiring, with a volt meter and an ohm meter , then you will probably be able to find the problem.

You may even have to try things like open the circuit between the PCM and the fan relay to see if the fan still activates when you turn the key to the on position. If it does, you learn that something else may be grounding the relay circuit to acitvate the fan when you turn the key...so then you might work back toward the key/ignition switch. You can tryto find out where the fan is getting its power from when the key is switched to on. Does the fan come on with the fan relay removed and the key is turned to the on position? If so, that would tell you there is a power short circuit activated when the key is turned.

Kind of impossible to give you a step by step process to check out the integrity of the wiring, but I would try to minimize the variables you are dealing with by isolating the circuitry. Pull the fuses on circuits that you don't need to power up when you turn they key to troubleshoot the fan circuit, or whatever circuit you choose to focus on. You might even want to unplug temp sensor, map sensor, etc...any PCM input circuit that might be telling the PCM to act weird.
 
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In the long run, you should probably go back to the Power Distribution Center and turn it up side down to re-inspect the wiring where it may have been damaged by the mouse nest.
 
Double, tripple checked. Taking a break on the jeep for a few weeks. I had to trade off and drive the suburban down here, jeepie couldn't haul the trailor full of furniture without trying to kill me every time i switched lanes and hit the brakes.
 
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