North American Turbocoupe Organization



Alternator cycling on and off?
ILoveMyTC Offline
Senior Member
#1
A couple days ago, my 88 died on the way to work. Radio turned off, gauges dimmed, and then the car died. Towed it home, and charged the battery. Volt meter showed 12.1V while running.

Got a new alternator from autozone tonight, and dropped it in. Went for a drive, and once again, battery drained down and eventually died. So my wife brought the van and jumped me to give me enough charge to limp home.

Testing the new alt with the volt meter, it shows 13.8V for 10-15 seconds, then drops to 12.x volts, and cycles back and forth every 10-15 seconds. When it is actually charging, I there is a load on the engine and it drops 150ish RPM, then when the charging stops, the RPMS rise back up. I've never known an alternator to cycle on and off like this.

With this partial charging, I'm assuming it is easily overhwelmed when lights are on and fans kick on.

Anybody know what would cause this behavior? Thanks!
Nick Johnson
88'TC
97'LX
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FastN'Fried Offline
Senior Member
#2
Did the new alt come with a voltage regulator or did you have to reuse the old one?

Does it have the same behavior with everything (lights, fan, cabin HVAC, radio, etc) turned off?

You could start tracing the wires from the alt back to see where they lead and look for melted/damaged wires. An ohm test can help.

How are the battery cables/ends? I once had a 2000 Zx2 with near 2ft of corrosion under the negative cable insulation :S

Good luck, keep us updated!
1988 Canyon Red Turbo Coupe
Carrillo pistons +.030, ARP hardware, 3in exhaust, and a magnaflow
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TurboCoupe50 Offline
Posting Freak
#3
FastN'Fried Wrote:Did the new alt come with a voltage regulator or did you have to reuse the old one?
Isn't the regulator for '88 alts internal? Not mounted to back cover like the 2G units?
1988 Turbo Coupe331 AOD

1972 Comet GT

1969 Fairlane Cobra 428CJ 4-Speed
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Gman Offline
Member
#4
Sounds like you have a near short circuit in a load -- something that is dragging down and overloading the alternator periodically. I have no idea what might be doing that. The hydraulic charging pump motor in the Teves brake master cylinder might be a good candidate. Maybe somebody else on this board would have a better idea what to check, but you could disconnect the harness to that pump with the car idling and see if the voltage swings go away.
1987 TC project car
Red butt splice - boosting about a bar
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Skunk Offline
Junior Member
#5
IIRC, there is no thermal cutout on the alternator. It will put out the same V.A. untill something gives up. You can't just look at volts you need to see if the amperage draw on the alt is also dropping,

Its likely a poor ground, the excitation circuit or the fuse link. Take a good look at the aluminum alt bracket, is it kinda oxidized white powdery looking? If so its likely a ground problem.

John
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Jeff K Offline
Administrator
#6
Auto Zone spray can reman alternator = junk. You are lucky it works at all.

You need to check all major grounds, corrosion or damage to batt cables as noted above. A volt drop test on alternator output cable, batt cables, etc will tell you if you have a problem and where it is.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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ILoveMyTC Offline
Senior Member
#7
I'm starting to think you might be right about the junk autozone alt.

Just took break to do a volt drop test. It's making a consistant 14.2V now. Voltage drop on alt output to positive battery terminal was 0.112 and on alt case to negative terminal was -0.21. Those values are with lights, a/c, and both fans running for load.

Heres a video of how it runs when it is messing up:
https://www.youtube.com/watch?v=k27Xip0yTqo
Nick Johnson
88'TC
97'LX
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TurboCoupe50 Offline
Posting Freak
#8
BUT is voltage dropping because because idle drops or is idle dropping that causes less alt output??

I'd disconnect connector on alt till it can't charge and see if idle still varies...
1988 Turbo Coupe331 AOD

1972 Comet GT

1969 Fairlane Cobra 428CJ 4-Speed
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ILoveMyTC Offline
Senior Member
#9
Well of course it won't do the intermittent thing for me right now. Its working correctly. It did the same thing yesterday, perfect stable 14V when I leave work, and then within the 30 minutes of my commute, starts the intermittent crap and by time I get home. Last night, I pulled the 3 wire connector and it would idle stably, so I'm pretty sure the variance in idle is caused by the load from the alternator.

For diagnostic purposes, AC compressor is unplugged, climate control is off, and I wired up the fans to a switch for manually control. So I can rule those out.
Nick Johnson
88'TC
97'LX
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Gman Offline
Member
#10
Pump the brakes! Next time it acts up and you're not driving, try disconnecting the electro-hydraulic pump on the Teves and see if it stops.
1987 TC project car
Red butt splice - boosting about a bar
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