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Unread 03-17-2012, 03:40 PM   #1
wjledden
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99 Jeep grand cherokee 4.7 electrical

My 99 jeep grand cherokee couple night ago started runnign rough for 10 second the voltage on the guage went to 9v and the odometer disappears. Then it started running fine again and voltage went to 14. Started it the next day went down the street and did the same thing will not rev up until it comes back. And did not get better. AirBag light comes on and ABS light and Brake light. Checked voltage while it ran rough. it was 17.5 volts. I changed the alternator and started up fine ran for a while with the lights still on. went for a ride and did the same thing after 15 minutes lasted 2 minutes and came back Lights went away and odomenter came back. Now it does it once and a great while and but only for 10 seconds. Any ideas.

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Unread 03-17-2012, 08:54 PM   #2
HVACNY
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Clean and tighten battery terminals and cables.Id start there
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Unread 03-18-2012, 04:00 PM   #3
wjledden
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i cleaned the terminals. nothing changed
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Unread 03-18-2012, 05:45 PM   #4
HVACNY
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Check for codes using the key method,And have your battery checked,might need changing.What kind and how old is your battery?
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Unread 03-18-2012, 11:52 PM   #5
kfxnando
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also check out the connections on the alternator itself, and all ground/negative/earth connections

good luck
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Unread 03-19-2012, 08:51 PM   #6
wjledden
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Checked it all hooked up computer. All signs are pointing to a bad PCM which i have found 160 bucks programmed and guarenteed. All the reading and testing i have done. these jeeps have a secondary voltage regulator in the PCM
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Unread 03-20-2012, 07:00 AM   #7
Double E
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Hope that's it for you but it points to a weak battery connection for the rest of us.

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Unread 05-14-2013, 07:01 AM   #8
wjledden
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Update!!!! So i found when i unplug the alternator. The truck runs fine. Plug it in runs full field from the alternator. I did a little research on ALLDATA and found the alternator voltage is controlled by the PCM. In ALLDATA it says if voltage regulator is bad you need to replace the PCM.So I bought a PCM online for 218 delivered. I put in the new PCM plugged in the alternator and BAZAAAM truck is fixed. Just wish i looked at alldata a year ago because i would not have had the truck sit for a year!!!
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