98 Grand Cherokee Laredo Charging issuse?? - JeepForum.com
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Unread 01-02-2009, 10:08 AM   #1
the_real_Kazman
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1998 ZJ 
 
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Location: Ontario, Canada
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98 Grand Cherokee Laredo Charging issuse??

I all new to the forums, great looking place here.

Here is the problem. I have like mentioned a 1998 Grand Cherokee Laredo. 4.0L auto/AC 4x4. All of a sudden the charging system has been acting up, it will be fine, then drops to 11 volts for maybe 5 10 minutes, then to nothing and the "Check Guages" light comes on. I have had the alternator tested 3 times.. (It's Good) Fresh battery, (it's Good too) Cleaned all my connection to and from the alternator and battery (so good too) Still have a problem. Oh and the belt tension and condition are good also. So the question is, what have i missed?? It happens at least once a day, I will start it, and it will go to 11V first for about 30 seconds, and then most of the time it will climb to 14V, but many times it won't. So please if you have any ideas or thought, don't hesitate to help this noob to the forums out, in what ever way, shape or form you may have. Also if someone as a schematic strictly for the charging system that they could post up, it would be greatly appreciated.

Thanks, and look forward to any ideas.

Oh and Happy New Year to all!!

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Unread 01-02-2009, 10:35 AM   #2
vdub
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if i remember right your battery gauge is not supposed to be at 14 volts. i think its supposed to be right under it. When i start my jeep and it sits idle the voltage gauge is like right about the 9 volt. then when i drive it climbs to like 13
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Unread 01-02-2009, 03:08 PM   #3
the_real_Kazman
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Thanks for you thoughts, but yes the gauge should infact be right around the 14 volts at idle at all times, with the battery voltage around 11-12 volts by itself the alternator charge brings the combined value to the mid 13-14 volts.
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Unread 01-02-2009, 03:51 PM   #4
vdub
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well jeesh then something is wrong with my jeep.. my voltage is always low then
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Unread 01-02-2009, 03:58 PM   #5
ZeeJay1997
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If you have a DVM, do voltage drop checks on the pos and neg cables, all connections, including the alt ground.
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Unread 01-02-2009, 05:24 PM   #6
the_real_Kazman
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Yeah, I even put a brand new ground wire right from the alternator right the the Neg battery terminal. After doing so, it was fine the first 3 times I started it, went right up to 14V right away, went in the house for an hour or so, went back out and started her, bang only like 11V again. Getting worried I have a ECM issue...
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Unread 01-02-2009, 07:25 PM   #7
ZeeJay1997
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You probably should check the wires from the PCM to the field terminals. Pull the PCM plugs and clean them. I dont know about a 98, but on a 97 the field wires (DG-neg and DG/VT- pos) go through a connector by the PCM. From there the DG goes to anther connector down behind the battery and on to the Alt. The DG/VT splices at the trans control relay in the PDC and on to the Alt.

I believe the DG/VT will be white PCM plug (B) pin 10. The DG is different depending on the PCM you have, but it will be on the gray plug.

Try pulling those all connectors apart and cleaning them. Or just do a voltage drop on them by pulling the covers of the PCM plugs and back probing the wires at the plug and other lead on the field terminal
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Unread 01-02-2009, 08:51 PM   #8
the_real_Kazman
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Quote:
Originally Posted by ZeeJay1997 View Post
You probably should check the wires from the PCM to the field terminals. Pull the PCM plugs and clean them. I dont know about a 98, but on a 97 the field wires (DG-neg and DG/VT- pos) go through a connector by the PCM. From there the DG goes to anther connector down behind the battery and on to the Alt. The DG/VT splices at the trans control relay in the PDC and on to the Alt.

I believe the DG/VT will be white PCM plug (B) pin 10. The DG is different depending on the PCM you have, but it will be on the gray plug.

Try pulling those all connectors apart and cleaning them. Or just do a voltage drop on them by pulling the covers of the PCM plugs and back probing the wires at the plug and other lead on the field terminal
Thanks for your input, I will try this 1st thing in the morning. You seem to be knowledgeable, do you have a schematic by chance for the charging system???
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Unread 01-02-2009, 09:23 PM   #9
ZeeJay1997
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ya, it's for a 97. Not sure of the differences, but wire colors should be same. PM me your email
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Unread 01-03-2009, 09:47 AM   #10
the_real_Kazman
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Thanks very much for the info!! That is exactly what I was looking for. Now I just have to wait for my wife to get home from work so she can watch my two boys. Once I have gotten dirty I will post my findings.

Thanks Again!!!!!
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Unread 01-03-2009, 11:19 AM   #11
ZeeJay1997
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You say you've had the alt checked...
How old is it?
Do you get less than 5 ohms across the field terminals as the pulley is slowly turned?
My charging system load checked good and the alt brushes were worn out.
This is indicated by the face of the PCM under the pugs being unusually warm because the regulator is over loaded.
Just something else to check before you call the pcm bad.
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Unread 01-03-2009, 12:16 PM   #12
the_real_Kazman
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I had it tested when It was removed. The local Canadian Tire.. ( like Autozone, but better) it was tested on a machine that they hook it up too. This machine actually runs a belt/motor system to crank it to 2500 rpms, then tests.

As for the alt age, I am not sure. I bought the Jeep used in 2003 and it was on there since I bought it. It doesn't appear to be OEM mind you.
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Unread 01-03-2009, 01:48 PM   #13
JrMechanic
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Mine does this when I come to a stop on occasion. Mine stays right past the 14 mark, then sometimes I stop, and my lights dim and it drops down to 11 or so... I've done everything you've mentioned, so I think im just going to leave well enough alone...
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Unread 01-03-2009, 03:30 PM   #14
the_real_Kazman
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Quote:
Originally Posted by JrMechanic View Post
Mine does this when I come to a stop on occasion. Mine stays right past the 14 mark, then sometimes I stop, and my lights dim and it drops down to 11 or so... I've done everything you've mentioned, so I think im just going to leave well enough alone...

That sound like you could be looking at some type of unwanted load on the vac system. Break booster or something more along that line. Or worse case a fuel system problem.
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Unread 01-04-2009, 01:46 PM   #15
the_real_Kazman
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OK so I did all the test on the system within the info you sent me. Everything checked out good. I then proceeded to clean every ground I could find in the engine bay. I even pulled on the fuses from the Fuse box under the hood and checked and cleaned them. So after all this I start it back up and everything seem great. I take it for about a 10 minute test drive with no problems. I stopped at the liqour store (LOL) and when I come out and start it back up, it is back to only around 11V on the gauge and then within 2 minutes of driving it dropped right off, and the check gauges light came on. Now here is where the weird part begins. Once home, I put my DVM on the battery and it states all is fine, running around 13.9 to 14 Volts. but yet the gauge is still bottomed out at 9V. Now I cannot believe this was all just a Gauge problem, as many times the battery did infact go right dead when the Check Gauge light came on after barley making it home. I FREAKING HATE WIRING ISSUES!!! LOL!!!
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