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Tim Mohr
Tim Mohr, ASE MASTER TECH
Category: Jeep
Satisfied Customers: 15114
Experience:  30 YRS EXPERIENCE, FOREIGN AND DOMESTIC, GAS AND DEISEL
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I had the alternator replaced on my jeep...now the battery

Customer Question

i had the alternator replaced on my jeep...now the battery light goes on only at 3100 RPM and goes off when back under 2900 RPM ???? 2008 grand Cherokee 3.0 Diesel
Submitted: 1 year ago.
Category: Jeep
Expert:  Tim Mohr replied 1 year ago.
Hi, my name is ***** ***** you have a volt meter? we need to see what the voltage is at the battery, when the light comes on?
Customer: replied 1 year ago.
Wow. How do you expect me to read this when i am driving at 3100 RPM doing 80 miles/hour. Any other hints?
Expert:  Tim Mohr replied 1 year ago.
will it come on when in nuetral, when reving the engine?
Customer: replied 1 year ago.
Nope
Expert:  Tim Mohr replied 1 year ago.
was it doing this before the alternator was replaced, or was the alternator not charging at all?
Customer: replied 1 year ago.
The light was always on and alternator was not charging at all. I had it replaced and now...let's say i am doing 50 miles per hour and i step on gas to pass a vehicule or anything else. As soon as i get to 3100rpm, the light comes on. I even made a video of it
Expert:  Tim Mohr replied 1 year ago.
This is most likely a bad voltage regulator in the new alternator, its not under charging, most likely over charging at higher rpm's, but we need to see what the actual voltage is when the light is coming on, the only way to do this when driving is with a scanner hooked up to the computer when driving, if the voltage goes over 15 volts when the light comes on, then you have a bad regulator in the new alternator, where did you get the alt from?
Customer: replied 1 year ago.
I had it replaced by the jeep dealer. Could it be related with the transmission since it down shift in 4th gear when i step on gas . I also tried to manually shift it down in 4th gear and i was able to have the light to turn on and off as i was playing with the gas pedal to go up and down in the RPM range between 2700 and 3300
Expert:  Tim Mohr replied 1 year ago.
No, this wont have anything to do with the transmission, I would take it back to them and have them drive it with the scanner on, it should be very easy to verify on a test drive, if it was nit happening before the replacement, it has to be a bad regulator in the alternator,Tim
Customer: replied 1 year ago.
I got to bring them back the Jeep on Monday morning. The electrical specialist will be back from vacation Monday morning. Thanks Buddy!
Expert:  Tim Mohr replied 1 year ago.
Anytime my friend, Please dont forget to rate me so I can get credit for helping, thanks in advance,Tim
Customer: replied 1 year ago.
Fyi...
Was testing my jeep this morning. I was manually shifting in 3rd gear, then i was able to increase rpm to higher revolutions. The tricky thing is that as soon i manually shift it in 4th gear...the battery light comes on.
Expert:  Tim Mohr replied 1 year ago.
Before we go any further, its neccessary to know the exact voltage when the light comes on,Tim

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