lavendje

Well unless the used ECU had the same issue "which I dought" the same issue has occured. I put in the used computer and drove it for about 1/4 mile and it came on. So now I am left woundering what is going on. Every morning I check the battery voltage 12.43v and then turn it over and check the voltage 14.01v or higher. I then turn on the head lights 12.83v and droping slowly, very slowly. I rev the engine it slowly climbs in the the 13v range. I let off and it drops back down to 12.83v and slowly drops. I drive the vehicle for 10.3 miles I can see the headlights get brighter and the voltage goes back up to 14.01v. I think I heard a faint click as it happened. This happens every morning even if I let the car fun with the lights off for 15 minutes prior to driving it with the lights off.
Is there a way to test the battery temp sensor?

lavendje

Well I have been trying to figure this thing out. I went to Autozone and now I am going to replace the Battery temp sensor. I figure there is no one in the Jeep world that has ever come across this issue, so I am hoping that when I figure this out and get it fixed, this will help someone else from having to go through all of this.

thorguy57

I had no idea there was a battery temp sensor. Have you ohmed out the Dk Green wire that goes between the ECM and your alternator for the field current? I would pull off both connectors and check the resistance of this wire. It could be it has a high resistance on it or barely connected by a few strands. Does anybody know if an alternator off an older jeep can be installed on these that has an internal regulator rather than one controlled by the ECM?

thorguy57

You also said you checked the battery voltage. My book shows TWO 60Amp fuses in the PDC under the hood. Did you pull these out and check both of them? Also when it is not charging try checking the voltage either right at the alternator or at the conductor off of the alternator

lavendje

I have the MRM for the 1999 4.0 Cherokee and I don't see the 60amp fuses listed. Do you know which one's they are in the fuse box in the engine compartment? I had a load test done and a circuit test done but both were done after the system started producing the correct voltage. I have to wait till the engine is completely cold to test the circuit other wise is passes everything.

lavendje

I ohm'd it out and it was 10.1K ohm's. I have no idea what the actual ohm's should be and this was done when it was warmed up.

It is like some how there is a switch that when a heavy load is put on it, it is supposed to trip the circuit and allow more voltage/amps to be produced and it is not allowing it until it gets heated up. Does that make sense?

thorguy57

Was the ohms on this the ohms on your battery temp sensor or the wire going from your ECM to your Alternator? It will be the Dark Green wire. I am not familiar with the battery temp sensor. What does it do? My book show fuse 8 and 16 for the battery in the PDC but I will have to go check on mine.

thorguy57

Well my manual says that there are two fuses that fuse power going from the alternator to the battery but I don't see them on my Jeep. All I have is the Haynees manual so the wiring diagrams kindof suck. Maybe there is a fuseable link in there somewhere? Did you try to change out your cable from your alternator to your battery?

thorguy57

Found info on the battery temp sensor. http://www.allpar.com/fix/codes/sensors/battery.html thats a new one for me. Looks like that is a possibilty but SHOULD be throwing a code. Of course that doesn't mean anything.

lavendje

I had a complete check of the charging system and everything checks good. It only happens when the engine and system is completely cold. They tested the cable connections and connections for shorts but could not find any. I guess I have to wait till it completely dies to figure this thing out.

lavendje

Well I though I would try to see if the ECM was working when it was warmed up and then put the cold one in to see if it resumed the cold start issue. Nope they worked the same at the same time which leads me back to the alternator I just replaced being bad again. I waited till the voltage started to go up and I heard the alternator kick in and started. When it is cold you don't hear the wine on the motor once it warms up and starts to work you hear it. Now how to get Advance to give me another alternator if its working when its warm. Its while under the initial heavy load that it starts to not work and then 20 minutes later it works fine.

lavendje

Well I finally got the second alternator replaced and it works great again. It was nothing that the Cherokee was doing to cause this. I went to a Jeep shop and got the computer tested and it was showing that the computer was telling the alternator to give it power but the alternator was not able to produce the power. So much for buying an alternator from Advance Auto Parts. I hope the new one lasts longer than 3 days.
I guess they were right about the computer it was rarely goes bad. So now I have a used one to get rid of.