The alternator in my car ('87 GL 2dr 4wd) doesn't seem to excite until around 4k RPM, which doesn't seem quite right. It uses the factory 3-wire setup and hasn't been modified, as far as I can tell. Found the receipt and it is a Schucks reman unit. I am completely green to these cars, is this correct?

 

I have searched through a number of different threads here and didn't find anything relating to the core problem, though the GM alternator swap does interest me. Has anyone used a Ford 3G alt in a Subaru? If so, was it worth the effort or just a pain in the butt?

Sounds like the regulator isn't seeing the reference voltage from the main junction. Check that you have voltage on the sense wire and the voltage warning lamp wire to the back of the alt.

 

GD

Make sure all the connectors at the alternator are good and not corroded, brittle, or poor. Bad connections cause lots of electrical issues.

 

Lots of national chains and others test alternators for free, sounds like a good idea to go do that.

 

If you start seeing your Brake, battery and other dash lights faintly come on your alternator is definitely needs replaced/rebuilt.

It sounds like there may be a problem inside the alternator. Check to see if there is 12 volts on the leads to the rear connector. If you have close to battery voltage on the two leads while the engine is running at idle and the output voltage is below 12.2 volts then it appears the alternator is bad.

Thanks guys! I'll tear into it Wednesday evening (after my son goes to visit his mother) and report back with my findings.

I've got 11.8V at the top of the "T", 0.01V at the bottom of the T with the car off, running (but not excited) and running after being excited. However, the alternator is putting out 14.3V to the battery once excited.

 

I don't understand.

Edited July 16, 200916 yr by Redcap

Your alt is bad. I have had the same symptoms a few times. Light faintly flow, voltage meter droping, rev up the moter to 4 or 5 grand and its good for a little bit. Yep. Alts shot.

Your alt is bad. I have had the same symptoms a few times. Light faintly flow, voltage meter droping, rev up the moter to 4 or 5 grand and its good for a little bit. Yep. Alts shot.

 

Figures. Guess I'll hit the junk yard and look for a GM alt then, although I won't turn down a late-80s Maxima either.

Edited July 16, 200916 yr by Redcap

Your alt sounds fine to me - 14.3 is within spec. What you have is wiring problems. The voltage supply to the excitation pin on the alt is missing and the sensor line has high resistance. If you run it like this for long it will probably destroy the alt, but so far 14.3v sounds ok.

 

GD

I assume the wire color for the bottom of the 'T' was white/red and the charge warning light was ON when you read zero volts on the lead. This would mean the alternator is grounding the field circuit inside and turning on the warning light like it should be when the alternator isn't working. Now if the warning light wasn't ON then this could mean a problem with the external wiring.

The warning light was not on, nor has it ever come on unfortunately.

 

I tore into the car yesterday and found part of the problem. The threads in the block for the bolt that holds the tensioner down badly stripped out. So I tapped it to 3/8-16 and tightened it down. Still have to excite the alt by revving it up, but it holds tight at 14.5V.

Since you saw 14.5 volts when the alternator was working it means the internal regulator is good. It sounds like you may have a problem with the battery warning light circuit though. You say the warning light doesn't turn on at all. The light should turn on when you turn the ignition from OFF to ON without the engine running. If the light doesn't turn on then you need to find out why. The first suspect would be the lamp or bad socket connection for it. With the wire connector removed from the back side of the alternator there should be 12 volts on the wht/red wire when the ignition is ON. This is what excites the alternator field. If the lamp is not on (when connected properly) and there isn't any voltage on the wire (even when removed from the alternator) then there is an open connection between the bulb and the wire connection to the alternator. This may explain why you have to rev the engine so high to get the alternator to work. It may be self exciting somehow. Once it gets the field going it is ok.

I'll investigate tomorrow and post my findings.