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Voltage drop under acceleration; Voltage drops to 11.5 under acceleration
Topic Started: Mar 25 2014, 08:45 AM (495 Views)
mostcallmerob
Backyard Mechanic
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I believe mwebb may have covered this on a similar topic, but I think my situation is somewhat unique.

Some background info: 96' Metro Lsi 4/5. I put in a brand new battery 5 months ago along with a new alternator belt about 6 months back. In between those times I also upgraded the headlights to glass housings so I could fit brighter H4 bulbs, and installed a relay.

The car starts up just fine and idles fine, but when accelerating the volts drop to 11.0-11.5 along with headlights/interior lights and all that dimming bad. If I am driving without my headlights on and turn them on, the radio shuts off and starts up again after "booting up." If I come up on a hill and let off the gas the lights brighten back up, voltage jumps to 13.2-13.5 and everything seems fine, but even under the slightest acceleration it will drop again.

The battery terminals are clean and tightened, plus I replaced them when I put in the battery. I am leaning towards the alternator, but don't want to drop that kind of money. Any suggestions are welcome and appreciated. THanks :popcorn
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evmetro


I don't know if this is the case for you, but it is possible to have a faulty alternator that only fails with increases rpm or increased load. Rare, but possible. Something about a broken winding that only opens under stress, then has continuity at rest. It is also possible to buy a new or re manufactured one that is faulty. I would put an amps clamp on the alternator lead and then rev it up to witness what it is doing.
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Silver2K


After about 6 months my alternator belt gets pretty loose and I start having symptoms, like bogging from a stop. My theory is the belt gets loose, slips under acceleration and loses regulation. Anyways try tightening your belt. It's cheap thing to try.
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David95237


Silver2K
Mar 25 2014, 11:56 AM
After about 6 months my alternator belt gets pretty loose and I start having symptoms, like bogging from a stop. My theory is the belt gets loose, slips under acceleration and loses regulation. Anyways try tightening your belt. It's cheap thing to try.
:gp
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mostcallmerob
Backyard Mechanic
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I'll clean and tighten all the grounds, tighten the alternator belt, and inspect the wiring tonight and report back with any changes.
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sheananigans


I would say +1 for a bad alternator. Grounds is also pretty likely, best thing you could do would be to go get your alternator tested at pepboys even if only so you can rule that out as an issue. Honestly to me it sounds like a bad diode in the alt. It wouldn't be the belt slipping, any amount of slipping from the belt would be heard as a loud squeal. Also you would notice the engine overheating as the water pump is on that belt as well.
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