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87 Turbo Sprint Alternator Not Charging AND NO idiot light
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Author:  Nofur Trunions [ Fri Mar 31, 2017 12:20 pm ]
Post subject:  87 Turbo Sprint Alternator Not Charging AND NO idiot light

IDIOT LIGHT: Idiot light checks OK when IGN ON & engine not running.

TESTED GOOD: Checked good at Advance Auto and that included a Sense test.

WRONG ALTERNATOR?: EDIT( NO, found tag on alternator and it is a 2-wire IGN & L) The alternator I was using was from a 1991 Metro - it was a Misubishi w/3pin connector. The Base 87 Sprint uses a "Electronic Engine Control" pin as per the 87 FSM - the Turbo, the simple 2-pin IGN and Lamp. When first installed, charged around 14.5 just fine.

STRANGE BEHAVIOR: Just before I took it to Advance, I tested battery voltage on car at start up and got weird results: 12.6v @ OFF, Start engine, next 10 seconds voltage increase uniformly to 13.7v, then just as slowly dropped to 12.2v

OIL FOULED?: Lots of dried, caked oil behind the pulley - so much Advance guy immediately thought it was going to test bad. Could flush with CRC electric motor cleaner. Might pull back off and check connections for corrosion or looseness.

SHUNT TEST: When I reinstall for 2nd attempt, if no charge, will measure current to see if there is a trickle present which might explain Idiot Light not coming on.

UPGRADE: If I get a new alternator, thinking about the 70-80 amp Ford Probe and Mazda 626/MS-6 units which are small and bolt right in - the connector is an oval I believe so I'd have to make an adapter since would never cut wiring harness.

Author:  87paperchuckerTurbo [ Tue Apr 04, 2017 6:05 pm ]
Post subject:  Re: 87 Turbo Sprint Alternator Not Charging AND NO idiot lig

It may just be me but I'm having a hard time making sense of what you posted and what your actual problem is. So I'd start with checking your cranking voltage on the battery. If the alternator did test okay and the battery shows 12.6 what is it while cranking? if it drops below 10.5 (I think I'm a bit rusty on my starting charging knowledge) the battery is toast. Next I'd check the quality of connection you have at the terminals and your alternator as well as your grounds. After that I would go through and do a voltage drop test on any and all wires that have anything to do with your charging system. Don't use the math method just take a multi meter and go from one end of the wire to the other a wire shouldn't be using any voltage. I go voltage drop over checking a wires resistance because you can have continuity on a broken wire that has but one strand in tact however that wire would appear abnormal on a voltage drop test. Google how to perform the test and have a ball I bet you'll find your issue fairly quickly. I hope I'm being helpful :buzz:

Also keep in mind a 12v battery in a vehicle typically should read more than 12 volts and I believe 14.7 charging.

Author:  top down@-40 [ Tue Apr 04, 2017 8:07 pm ]
Post subject:  Re: 87 Turbo Sprint Alternator Not Charging AND NO idiot lig

Check the large wire coming off the alternator connector that runs to the battery. They have been known to cause problems at times.

Author:  JamalSpelling [ Tue Apr 04, 2017 10:03 pm ]
Post subject:  Re: 87 Turbo Sprint Alternator Not Charging AND NO idiot lig

All good advice. Voltage drop test will show you where the problem is if you
believe your alt is in good working order.
Check the plug on the alt as well for damage, or melting (resistance generates heat).
I suspect a different plug has been wired in to run the Geo Alt?
Check the fuse and fusible link. And try being more specific as to the
actual problem so we can help.

Author:  Nofur Trunions [ Fri Apr 07, 2017 12:22 am ]
Post subject:  Re: 87 Turbo Sprint Alternator Not Charging AND NO idiot lig

THANKS all for the tips!

Everything pointed at a wonky VR - so I resoldered everything on the VR/brush assembly hoping the heat would either "fix" it or produce a complete failure..

That did it in: no charge AND idiot light ... well, I don't remember. (I took it to AutoZone and the VR was operating at something like 10.5 volts (instead of 14.5v) which would explain why the idiot light never came on.)

So I got a $61 lifetime proper Denso from PepBoys. Just installed it and everything seems to work OK.

I think the VR was simply failing.

Now on to the crappy OE radio.... starting new thread....

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