'86 GT 2.8 V6 Charging System

Failure of one or more diodes can cause the maximum charging current to be low. This can cause a low battery condition when lights or air conditioning are being used but adequate charging when loads are low and trips are long enough for the battery to become fully charged.

Since I do not know your skill level or the mechanics of your alternator I would suggest having it tested. In our area most of the auto parts stores will test it for free.

Don Young

A number things come to mind in order of most likely occurance.

1- worn sticky brushes 2- blown triode 3- dirty connections (this could be #1) 4- regulator (maybe)

Also the voltmeter in the dash would not be as good as your DVM but the fluctuations dont sound good. Why not put your DVM across the battery terminals with the engine running and see what you get. Perhaps set at 200v scale to cut back the 'hunting'. As mentioned you should be able to get a free test of the battery but be aware of the reason they do them and the advice offered :-)

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Cheers ............. Rheilly P

The voltage regulation on just about any modern car is set about 14.5 volts -- or more -- not 13.5. No. With a healthy charging system and battery, your voltage should come up to 14.5 pretty soon after starting the car (as measured with a decent digital meter, not the dash gage).

Some reasons the voltage might be low:

Battery going bad (probably not the case here).

Battery that has been deeply discharged. A battery that's low enough can suck up all the alternator power, holding voltage down. But eventually, as the battery charges, the voltage will come up.

Bad voltage regulator. But they are either good or fail altogether. A voltage regulator causing mere inaccuracy or weak charging is unusual. I wouldn't think first of a bad voltage regulator based your description of the symptoms.

A bad diode in the three phase six-diode pack. Note that in floating field alternators such as the Delcos used on GM vehicles, there is another set of diodes besides the heavy rectifiers: the exciter diodes. The exciter diodes are much smaller than the output power recitifiers because the exciters only have to carry the field current. But if you open the alternator to check the heavy rectifiers you should also check the exciter diode pack. It has three diodes in it. I don't know if they still look like this, but on the older alts I've worked on the exciter diode pack is a little orange rectangular plastic thing with three tabs on one side and a single tab opposite it. The three tabs are connected to the wires on the stator.

Corroded connections, either in the wiring harness or inside the alternator. When I bought my used 86 Burb, it would hardly charge at all. Opening up the alternator, I found heavy rust and cobwebs. Unscrewed the connections and scraped everything clean, now it charges like a champ. Apparently it sat for years in heavy humidity. You should also check the wiring harness connections that carry any substantial current. Like the battery connections and ground strap, for example.

Pulley on the alternator too big. This results in an alternator that turns too slow at idle to charge. I had that problem on an old car I owned once.

There's more, but I'd need to know more about your particular car to go much further.

talking about that. we had a New electronic shift transmission replaced in our (92) dodge once. the transmission had sticky torque converter in it but also exhibit some problems with shifting.. after the replacement, the care seem to be better but after about

5k miles, the shifting problem came back and just got worse.. it was a $1800 repair job and except for the torque convert not sticking any more the shifting problem was still there. so we visited a dealer! their answer was, "You need a new transmission, there were problems with them", our answer" we just got one ! see our warranty!", we ended up parking the car eventually due to it's severity to not always shifting into 4th for highway use. -- then i donated the car to a friend for around town use --- the alternator let go on them after about 6 months., they replaced it. guess what! the car shifts perfectly now and she is happy as hell knowing that she now has a car with a new Tranny that can go anywhere costing her nothing.

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On Sat, 14 Oct 2006 01:29:22 +0000, Rich Grise wrote: ...

Thanks to everyone for the answers - I believe my next step is to take it to the shop. I used to work on my own car, when I was 20 years old and you could climb into the engine compartment, but I fear those days are long past. ;-)

Thanks! Rich

Rich,

It really sounds like it is time to install a rebuilt or new alternator which on a Fiero is no walk in the park. I wouldn't want to do it on mine and it is only the 4-cylinder model so there is a bit more room.

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James T. White

I replaced my '88 V6 standard with a 160 amp unit, trust me I'd rather do the V6 than the 4 cyl engine.