Diagnosing Intermittent Charging Problem - JeepForum.com

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post #1 of 10 Old 12-13-2013, 11:55 AM Thread Starter
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Wj Diagnosing Intermittent Charging Problem

Have run out of ideas, and turning to the forum for help. Here're the particulars:

-`99 Grand Cherokee Limited, 4.7 V8, 160K miles, all stock
- vehicle starts fine, voltmeter shows 14+ volts at idle
- drive down the road five miles or so, and voltmeter starts to drop
- drive far enough, and warning chime announces "Check Gauges"; voltmeter shows below battery voltage; shut the engine off, and it won't restart - battery flat. The three times that's happened, if jump-started, it starts right up and shows 14+ volts again.
- at times, when slowing to a near-stop, the voltage will come back up to 14V and remain there
- at times, during or after the "event", transmission seems to attempt to downshift, then upshift; what's felt is a driveline shock like a "kick in the rear"
- have experienced only one DTC - P0108 - MAP sensor; sensor tested okay at 4~5V from outside wires to ground (plug disconnected, key on); voltage from center wire to ground fluctuates with TPS movement
- at times, when the engine is below operating temperature, when coming to a full stop in gear, idle speed will drop low enough for the engine to stall. Starts right back up. Idle speed seems to stabilize at 650 after a brief higher level.

I can't say for certain how much of what I've described is connected to one another, I'm just throwing everything out there in hopes someone can make sense of it all.

There are no other problems I've observed. Temperature controls, heated seats, lights, windows all seem to work fine.

What I've done so far:
- replaced battery & clamps
- confirmed ground cables connected and active at cylinder heads, right front fender at power distribution box; engine to body, exhaust to body
- tested MAP sensor as noted above
- tested alternator both with Auto Meter hand-held and off-car: passed all checks.
- looked at the wiring going into the driver's door; there appears to have been a previous repair in there, but it's too cold to work on it right now.

At present, this vehicle is not reliable to drive, so I'm writing this with fingers crossed, hoping someone else has been down this road to a fix. Any help will be appreciated.


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post #2 of 10 Old 12-20-2013, 06:36 PM Thread Starter
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Wow. No ideas at all?

Update: repaired broken wire in driver's door bundle. Door controls now reliable, but charging issue was uneffected.
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post #3 of 10 Old 12-20-2013, 06:39 PM
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Just throwing it out there...maybe the brushes in the alternator loose contact once it heats up. No contact, no charge. I would try swapping the alternator, can't hurt and worth a shot!
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post #4 of 10 Old 12-20-2013, 07:57 PM
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Doesnt this trans have an issue with speed sensors causing idle issues after a complete stop. Hopefully someone else will chime in. It could be at the least PART of the problem.
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post #5 of 10 Old 12-21-2013, 12:28 AM
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99% sure the alternator is toast. It checked out ok because it is an intermittent failure. Stalling, DTC for MAP, etc are all flukes related to low voltage; ignore. The new battery's life won't last very long without a fully operational charging system, you might need to replace as well once you replace the alternator (unless it is a dry cell battery).
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post #6 of 10 Old 12-21-2013, 01:12 AM
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How are the wires running from the battery themselves? Could there be corrosion inside of them? Also how are the wires that go to the alternator? Any sign of corrosion at all?

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post #7 of 10 Old 12-22-2013, 11:50 AM Thread Starter
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Thanks for the suggestions - all help is appreciated!

Update: no-charge situation is now constant. Only thing new so far is that I found the ground strap from the body to the transmission frayed to the degree that only a few strands were holding it together (it lies on top of the exhaust pipe on its way to the trans, and I guess the years of vibration wore it through). I missed that before. Will get a new one this week.

Suggestion about the alternator seems a good one. It's been tested four times so far, both on-car and off, but now that the no-charge is constant, maybe the problem will show up on the fifth test?

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post #8 of 10 Old 12-22-2013, 02:48 PM Thread Starter
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Second update: alternator failed testing this time, and a remanufactured unit is charging as it's supposed to.

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post #9 of 10 Old 12-22-2013, 08:14 PM
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Glad it's all squared away and running properly!
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post #10 of 10 Old 12-23-2013, 09:09 AM
Double E
2000 Laredo V8
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That ground strap is nothing more than an improvement to the AM radio reception. Doesn't hurt to fix though.

The alternator is certainly the issue. I was able to squeeze a few more miles from it by smacking the housing with a hammer. It was done though. Same symptoms as you.

You'll do a little better with a replacement by getting the Durango replacement alternator. It costs less too. Direct fit and puts out 160 amp as opposed to about 128 from the Jeep unit. The only small modification is the diameter of the copper ring connector to the alternator....it needs to be opened up slightly to fit.

For Sale! - 00 Laredo 4.7 Selec-Trac. 215K miles, Leather, aluminum radiator, trans cooler & sunroof.
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