Alternator dipping

Nixon1 · 04-11-2003, 03:11 PM

Lately I've noticed at a low idle my alternator's output, according to the gauge, seems to drop. When in gear, after I've been sitting at a light or something for a fair amount of time, the output on the gauge drops by about 3/4 of a bar, then back up again.. It's not spiking, it's dropping, since it holds the higher output longer than the dips last. Out of gear, like in park, it also drops, but more drastically, but also at a less frequently and unpredictable rate. There is no change in the car's idle in correlation with this, although the idle is not as smooth as I would like it, fluctuating by about 50 rpms continuously and missing occasionally. The alt output never dips below the normal area, but usually it is on the lower end of normal. Is this normal behavior or is something wrong? Thanks!

Mustang_289 · 04-11-2003, 05:28 PM

Do you have a stock alt? If so, they're either 65 or 75A units - not much power. Do you have under-drive pullies or a large amp on your stereo?

To check what's going on - first, have your car idling and take a DVM across the battery - should be reading about 14.0-14.5 volts. If it's less than 13 you've got alt problems. Next, turn many accessories on and take another reading. If voltage drops this is an indicator your alt doesn't have enough juice for your car.

If you need to replace - go with a bigger alt. Got mine from PA Performance - lifetime warranty and great support!

Nixon1 · 04-11-2003, 07:53 PM

Stock alternator, stock pulleys, no stereo equipment. I've got a voltmeter sitting in my tool kit..I'll grab it and do this test tomorrow and see what I find. 65/75 amps is wimpy as hell! No wonder it doesn't read much on that gauge!

04-11-2003, 03:11 PM	#1
Nixon1 Registered Member Join Date: Jan 2003 Location: Palm Bay, FL Posts: 432	Alternator dipping Lately I've noticed at a low idle my alternator's output, according to the gauge, seems to drop. When in gear, after I've been sitting at a light or something for a fair amount of time, the output on the gauge drops by about 3/4 of a bar, then back up again.. It's not spiking, it's dropping, since it holds the higher output longer than the dips last. Out of gear, like in park, it also drops, but more drastically, but also at a less frequently and unpredictable rate. There is no change in the car's idle in correlation with this, although the idle is not as smooth as I would like it, fluctuating by about 50 rpms continuously and missing occasionally. The alt output never dips below the normal area, but usually it is on the lower end of normal. Is this normal behavior or is something wrong? Thanks! __________________ '91 Mustang GT 5.0 AOD Daily Driver Current stats: NEW 302 short block, E-303 cam (@.050, 220/220, .498/.498, 110 degrees), 1.6 roller rockers, Performer RPM heads (aluminum, 1.9/1.6, 60cc chambers), Cobra intake, Granatelli 75mm MAF, Billet AFPR, Equal-Length Shorty Headers, Off-Road X Pipe, Flowmasters, 4.10 POSI 13.73 at 103.8, ~2.2 60'

04-11-2003, 07:53 PM	#3
Nixon1 Registered Member Join Date: Jan 2003 Location: Palm Bay, FL Posts: 432	Stock alternator, stock pulleys, no stereo equipment. I've got a voltmeter sitting in my tool kit..I'll grab it and do this test tomorrow and see what I find. 65/75 amps is wimpy as hell! No wonder it doesn't read much on that gauge! __________________ '91 Mustang GT 5.0 AOD Daily Driver Current stats: NEW 302 short block, E-303 cam (@.050, 220/220, .498/.498, 110 degrees), 1.6 roller rockers, Performer RPM heads (aluminum, 1.9/1.6, 60cc chambers), Cobra intake, Granatelli 75mm MAF, Billet AFPR, Equal-Length Shorty Headers, Off-Road X Pipe, Flowmasters, 4.10 POSI 13.73 at 103.8, ~2.2 60'

04-11-2003, 05:28 PM	#2
Mustang_289 Registered Member Join Date: Sep 2001 Posts: 512	Do you have a stock alt? If so, they're either 65 or 75A units - not much power. Do you have under-drive pullies or a large amp on your stereo? To check what's going on - first, have your car idling and take a DVM across the battery - should be reading about 14.0-14.5 volts. If it's less than 13 you've got alt problems. Next, turn many accessories on and take another reading. If voltage drops this is an indicator your alt doesn't have enough juice for your car. If you need to replace - go with a bigger alt. Got mine from PA Performance - lifetime warranty and great support!