volt meter and battery light

95,085

Asked by Mar 05, 2013 at 10:27 PM about the 1996 Isuzu Trooper 4 Dr Limited 4WD SUV

Question type: Maintenance & Repair

Volt meter reads normal, about 14 volts at idle and battery light is off, if you accelerate like climbing a slight hill or passing on the freeway the voltmeter drops to just under 12 volts and the battery light comes on, if driving at night you notice the lights also dim, back off the gas and everything goes back to normal. I was told it was the alternator so I replaced it and all of the belts, same problem, took out the new alternator and had it tested, and it checks out very good, the guy told me that this is a ECM controlled alternator and that might be the problem.  I put the alternator back in and checked wiring up the side and to the main plug in the engine bay, didn't find any problem there.  Anybody got any ideas?

12 Answers

the voltage regulator is part of the alternator...maybe you got a dud. It's not unheard of.

20,585

I think the troopers had a blue relay or something tied to the air cond. relay and one is for charge , look at relay box

1 of 1 people found this helpful.

..wow kinda guru-ey, just like the genie...

105

Your ignition modules(units the plug wire come from) could be failing and forcing the battery to supply the missing voltage during acceleration, or under load.

98,125

First thing that came to my mind is a broken wire or bad electrical connection. When the engine is under load, it moves in the mounts, pulling on a wire and the circuit opens. - Give the wiring a close look before throwing more alternators and ECU's at it.

2 of 2 people found this helpful.
Best Answer
70

I had a similar sounding problem once. What I found was the engine ground strap was broken and as the driving torque of the engine increased like climbing a hill or accelerating, the engine would lift just enough to loose the ground. This sounds impossible but ground the engine to the frame & engine to the battery and see what happens.

2 of 2 people found this helpful.
95,085

Thanks for everyone that responded to my problem. The problem was the ECM, for some unknown reason it would put the alternator into economy mode during acceleration. ECM replaced problem is gone. Happy Trails

5 of 5 people found this helpful.

please click 'mark helpful' for those of us who you thought were helpful. I gave you ten points....just 'cause I can~

1 of 1 people found this helpful.
20

Since the alternator is control by the ECM find out which wire from the alternator go to the ECM. Cut that wire so the ECM does not control the alternator anymore. My friend is a master mechanic and did that to his customer car. No more battery light and everything is ok

2 of 2 people found this helpful.

What is the part number for the ecm i cant seem to find it anywhere

95,085

It's right on the ECM itself, if the tag is missing then your in a world of hurt as there are no more dealers that can use the vin to trace the calabration code and get you the right numbers. You maybe stuck with using a R&R service, that is a place where you give them your ECM, they test and repair it and give it back to you. Not cheap. Or you can take a chance with a wrecking yard, find the same year with the same equipment and a build date as close as possible to yours and hope for the best. No guarantees there though.

Thank you i was also wondering what wire to cut that goes to the alternator

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