My voltmeter will read 13+ and everything will be fine until I turn something else on (doesn't matter if it's headlights, brakes, roll the windows, etc. it all does it) the voltmeter goes down to like 9, the engine loses a couple hundred RPM, and all the lights dim. Then after a few second with low power it'll go back up and be normal (until I hit the brakes or use my signals...).

The alternator was replaced last week and it's done this ever since. So I took the alternator and the battery into the parts store and both tested fine. The first time they tested the alternator it was putting out 8 volts, the next two times it put out 16+ (the out put fluctuating like it did in my car kinda), but nobody really knew how to work the machine so it could have been operator error.

I'm still thinking alternator and all the wiring looks good. Any thoughts?

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85 TA, 305 TPI, AT, T-Tops,
Russet Mettalic over Gold
My T/A's Page

 

hey is all of your ground wires hooked up good like the one running from the firewall to the back of the head on the passenger side of the car...also you might want to check your battery cabels and make sure they arent shorting out on the frame..If you have a autozone or advanced parts place where you live they can check your entire charging system on your car for free...

 

If it suddeny started doing this exactly when you replaced the alternator, it smells like the alternator you put on is fubar....

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"So many Mustangs, so little time..."

 

I am taking the alternator to an alternator/starter shop and they are gonna test it.

All the grounds look good and when I had the battery out yesterday I checked the terminals and the wires and everything was clean and looked good.

 

Alternator tested fine, the battery tested fine, all the grounds look good... There has to be somehting I'm missing. Because it should be working.

 

It's still doing it, I need ideas. It's getting worse and it's left me stranded twice now.

 

I just thought of something I did right before this started happening. I set my timing.

Shouldn't matter, but I'll retime it later...

 

I'd say to take that alternator back to where you got it and stand on their counter until they replace it. After all, their own tester said it was squirrelly, didn't it? It doesn't matter that their employees are ignorant; you just need a part that works. Don't let them force you to keep a bad part just because they're too dumb to prove definitively that it's really bad.

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"So many Mustangs, so little time..."

 

Did that last night, it's a completely different alternator today.

Sorry, I meant to mention that... oops

 

When you replace the alternator, you also need to replace the battery, don't ask me why, you just do. I found out the hard way?

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End

Current Mods: Edelbrock TES 1 5/8" Headers, Hooker Aerochamber Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET : 14.3 @ 97mph
(corrected for elevation)

 

Remove the 3 wire connector that plugs into the alternator. With key on to run position, check voltage at all 3 terminals. It should be the same as battery voltage. If you do not have voltage at all 3 pins, you have an open circuit somewhere. One of the pins is for the voltage regulator activation. If you don't have voltage there, the alternator won't charge.
Regards, FJK

 

MB,

I expect the parts store load tested the battery, and output tested the replacement alternator. That being the presumtion...

If you suspect your alternattor is not capable of handling the load, you can test maximum output using the test/bypass hole on the back of the alternator. Look for a "D" shaped hole in the back of the alternator, opposite side from the heat sink/diode bridge assembly. With a voltmeter connected and the engine idling, you can briefly ground the test tab inside the hole to bypass the voltage regulator and test alternator maximum output. Do this only long enough to get a voltmeter reading, since the higher voltage will likely set a code '53' and sustained operation in this mode can damage components that cost big bucks, like the ECM, EST, radio, SIR, cruise control, etc. Output should be over 15 VDC, and can get as high as 19VDC during this test.

If the voltage is not at least 15VDC the alternator is defective. If the test is successful, you may still have a failed regulator, in which case you should demand a replacement alternator anyway. However, if the voltage regulates correctly under light electrical load, the regulator is probably functioning.

Check the connections at the battery. A good time to do this is after you do the regulator bypass test, since you'll have to disconnect the battery to clear the fault codes. Clean both battery connections. Clean the body ground connection near the battery. Check the positive cable at the starter and the battery ground cable at the engine case. Check the positive power node connection near the batrtery, and look for signs of heating in the fusible links near the battery. Make sure the alternator output connection is clean and tight, and clean the field connections to the alternator.

More than likely, you have a failing connection somewhere under the hood, where everything is exposed to road grime and moisture.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

what brand is this alternator? if its napa take it back and get an autozone one!

Steve

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86 Firebird, LG4, t-tops, 2.73 open rear, SLP 3 inch cat back exhaust, catco cat, Coming mods: GOT A 350 IN THE WORKS BABY! gonna throw my TES edlebrock headers on it, and hopefully get some more gear and the cowl hood on

My Webpage- Battle of the birds, My own Thirdgen Page, still under construction, http://www.geocities.com/soares711/index.htm

88 Firebird Formula- deseased 2/9/99- 305 TPI, SLP 3 inch exhaust, SLP Intake runners, SLP cam, 3.45 BW disc brake posi, WS6, NOS, and all that good stuff, 13.8 on the motor, 12.89 on NOS and slicks! Hit by what else!?!? a FORD EXPLORER!!!!!!

 

Thanks for the tips, I'll look at it tomorrow and let you know what I find.

This is the second alternator and was bought at Checker, but at the moment I can't remember the alternator brand.