Alt Gauge Shows Severe Drop at Idle -- Probable Bad Alt?

[lobo411]

Updated...see most recent post.

I'm thinking it might be time to scrap her, but...1996 Explorer 4.0 OHV w/ 175k.

I was driving back from the post office today, and I noticed that my oil press and alternator gauges were quivering slightly (a sweep of 1mm in either direction). This was with the radio and vent on only. I drove home and parked the car, but left it at idle. Then I turned on some accessories, such as the a/c, the vent fan, and the headlights. The alt gauge showed a severe drop.

I have no idea what's going on...I hate electrical problems and it seems like they never really get fixed. But anyone have any ideas? The alternator is newish...3 years old, but only 15000 miles on it. Duralast Gold IIRC. I do have the old alternator (I had replaced it on general principles) so I'll probably try reinstalling that to see if it does anything.

The battery is a Costco Kirkland thing...Almost 5 years old.

Video below.

At 0:00: Engine parked, at idle, parking brake set. Radio and headlamps on.

0:06: I turned on vent (not AC). Alt gauge drops severely.

0:13: I turned off the vent. Alt gauge rose to normal.

0:17: I turned the vent back on. Alt gauge dropped severely.

0:23: I turned the headlamps off while keeping the vent on. Alt gauge rose to normal.

I don't really suspect the blower motor/circuit because I drive with the vent (not the AC, just the blower motor) on all the time and I've never seen anything like this.

Voltmeter readings:

Idle, with or without vent fan on: 14.4 VDC
Idle, with vent fan AND headlamps on: 13.4 VDC
Off, just the battery: 12.4 VDC

Idle, with vent fan AND headlamps on: Gauge shows low. Revving engine to 2000 RPM immediately restores full voltage.

 

[lobo411]

UPDATE: I replaced the Duralast Gold alternator with the old OEM alternator I had in the garage. Problem seems to be solved. Or maybe not?

 

[Mbrooks420]

Very nice. Still probably some life in that OHV still.

 

[lobo411]

Updated...see succeeding post.

Thanks! It's working better than before. I don't have the gauges quivering at idle with the lights off/a/c off, but I couldn't get the alternator tested because Autozone didn't have the necessary testing machine mounting bolts. They called 3 other Autozones in the area and all had the same issue. This is a Duralast Gold new/non refurb alternator.

The only option they could offer me w/o testing the alternator was an exchange, but they said they'd have the mounting bolt in a week or two. I opted to wait and see. If it tests bad, I can get a cash refund.

As I was driving home, I noticed I'm still getting what I consider to be an excessive drop. The issue seems to occur when I engage the blower motor on high, especially on starting the vent system.

0:00: Idle, in park, vent off, lights off

0:06: Vent fan ON, max speed, AC off.

0:08: Vent fan OFF.

0:10: Vent fan ON, max speed, AC off

0:15: Headlamps ON

0:17 Headlamps OFF

0:20: Vent fan REDUCED from max to minimum speed.

0:22: Vent fan INCREASED to max speed

0:25: Vent fan REDUCED to minimum speed.

0:35 Vent fan INCREASED to max

0:38: Vent fan OFF

0:41: Vent fan ON, at max speed

Video


I'll try to get voltmeter readings later.

 

[lobo411]

OK, the old alternator is still installed. I tested it with a voltmeter, and got the following readings:

Engine on, no other accessories on:
13.95 VDC

Engine on, vent on high, headlamps on:
13.85 VDC

I'm back to thinking that the issue was the Duralast alternator. I didn't realize that the blower motor on high draws a lot of current (I googled around and read something like 20 amps), so I guess it's normal to see a dip. It makes me more comfortable with the OEM alternator to see that it takes a dip but bounces back, while the Duralast alternator took a dip and stayed low.

Unfortunately, I can't get a solid answer on the Duralast alternator until Autozone gets the right bolt to be able to test it.

 

[Mbrooks420]

What not take it to a different auto store for testing?

 

[lobo411]

What not take it to a different auto store for testing?

For some highly technical reason. Not because I didn't think of it!

I'll try that tomorrow. Thanks!

 

[koda2000]

FYI: If you bought a Duralast Gold alternator from AZ, they're guarantied for life and you don't need to have one of their stupid disappearing paper receipts, because they can look up your purchase on their computer system using your phone number or name.

You may need to have AZ test it though to get it replaced, because they're supposed to verify that it's bad on their machine before they can replace it. If they don't have the part they need to test it, ***** to the manager and they'll most likely just give you a new one. I don't understand why they don't have the adpator/bolt to test it though, unless they managed to lose it.

 

[Rhett]

You should take advantage of that lifetime warranty, and you'll have a spare alternator.

That's what I did, I run a 130 amp Limited alt, and have an autozone 95 amp as a spare laying around.

 

[lobo411]

Thanks for the replies! The guy at Autozone said he was missing the offset mounting bolt, and that none of the 3 Autozones he called had it either. Apparently, they had ordered the part from the manufacturer, but nobody had received it yet. He did try to mount the alternator with the hardware he had, but he said it wobbled too much to get a reliable reading.

I took it to one of the other Autozones this morning, the girl put it on the tester, and she said it passed. However, I mentioned that I had installed the OEM alternator and it solved the problems (gauges quivering, voltage dropping and staying there w/ accessories, etc..), so she agreed to replace it. It's on order, though, so I'm still running the OEM alternator.

Everything is running fine with the OEM alternator right now...no more gauge-quivering, and when I turn on the accessories, the voltage gauge drops but it immediately bounces back into the normal range. So while the Duralast Gold alternator passed their tests, I think it was just starting to go bad. When I turned on accessories, the voltage gauge would drop and stay low.

 

[Mbrooks420]

Yeah, their tests are pretty lax. Mostly if it puts out a small amount juice, it passes. They don't really get a proper load test. I need to start stripping down my parts truck.