Voltage question (Page 1/3)
1985 Fiero GT OCT 11, 07:39 PM
Recently I have been observing some... Interesting behavior from my Fiero's electrical system.

Before I get into that, I do not have a factory Volt-meter. Instead I have a digital volt display located where the rear defrost switch goes, I have tested that and compared it to a multimeter, and it is accurate, also my fuel pump is somewhat audible, and the pitch changes discernably with voltage.

Now for my issue, voltage on startup is normal, climbing to 13.6 volts very quickly, Voltage varies by only about 0.5v either side of 13.6v. warm, cold, high rpm, idle rpm, lights on, radio on, etc. No lower then about 13 with everything on, no higher then about 14.1 with nothing on during "brisk" acceleration. That is how it normally acts.

Sometimes though, randomly, voltage will drop to below 12v, sometimes for a few minutes at a time, fuel pump will sound quieter (confirming voltage is lower and gauge isn't lying) lights (if on) will dim slightly. while that is happening voltage will continue to drop, at a rate that makes it seem as if the alternator is doing nothing, about .1v every minute or so. It has never to far below about 11 volts before kicking back up to 13.6, usually giving the engine a little rev kicks it back up, but it will often go back down within a few minutes. Usually this happens when the engine is warmed up, maybe that is the only time it happens, I don't know, but it can happen when cruising (no apparent connection to rpm, same chance of that happening cruising in town 1000rpm as on the highway 3000rpm)

I just replaced the engine to chassis ground strap and cleaned up the connections, car has very good overall electrical connections (kept clean and dry for whole life) so I am thinking the issue might be in the guts of the alternator or maybe the voltage regulator (don't know what part that plays in it, but based on the name, might be the issue.
P.S. my dad's Fiero has a similar querk, but due to not being driven much, I know a lot less about it, all I know is that upon startup the factory Volt-meter reads low, like 8-10v, then when the engine is gently revved, it kicks up to high voltage, like 16 (most likely inaccurate gauge, but it shows some difference) after that, voltage stays high for the remainder of drive (I think!) The alternator belt never makes any noise, and doesn't appear to be slipping, so probably just the way the alternator turns itself on.
Patrick OCT 11, 08:20 PM

I'd say your alternator is toast. Good time to upgrade.

Upgrade to CS130 alternator
1985 Fiero GT OCT 11, 08:27 PM
Ok, because this has been happening for a while, maybe a few weeks to a month, more often writing properly then not, which made me think maybe some intermittent short or some sensor not working, I know my car doesn't have ac, and it has the low amperage alternator, (60 something I think) so it would have been more strained over its lifetime then a higher capacity alternator. What is the voltage regulator and what does it do, cause if that is even a slight chance of being the problem, they are 15 dollars on Rock auto.
Spoon OCT 11, 08:35 PM
I believe I missed what engine you have, When I had a 2.8 the voltage would act sort of like yours. It would occur whenever the auxilary cooling fan would engage. Its located in the passenger side corner in the trunk. The voltage would be affected during this fan cycle to cool down the coolant. All Fiero's did not have this cooling fan. Perhaps that could be your issue which could be a non issue.

Spoon


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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

[This message has been edited by Spoon (edited 10-11-2023).]

1985 Fiero GT OCT 11, 08:43 PM
It is the 2.8 v6, should have mentioned that, although the "trunk fan"turns on at the same time as the radiator fan, and it never turns on during normal driving, it takes about 10 minutes of idling before it turns on (inaccurate gauge, but temp is well past red when it turns on, no boiling coolant/overheating cruises at middle of temp gauge (105*c)), all my driving is either 50km/h with traffic lights every km or so, or 60-80km/h open road driving. This has also been happening with the outside temperature fairly close to freezing (I remember the cabin heater fan rpm drops when voltage drops too) so it isn't related to the radiator/trunk fan

Edit: But yes whenever the fans turn on, voltage drops about a volt, maybe a little more, but the fan has turned on maybe a dozen times over the hat 12,000 km (almost no city driving/idling and no front license plate (better airflow)

[This message has been edited by 1985 Fiero GT (edited 10-11-2023).]

Patrick OCT 11, 08:45 PM

quote
Originally posted by 1985 Fiero GT:

What is the voltage regulator and what does it do, cause if that is even a slight chance of being the problem, they are 15 dollars on Rock auto.



The voltage regulator is inside the alternator. If you're keen to rebuild the alternator (it's not difficult with the old SI units), then yes, replacing the regulator can sometimes be an inexpensive and effective way to regain proper voltage.

I suggested the CS upgrade because these newer style alternators are much more efficient, especially at lower revs.

[This message has been edited by Patrick (edited 10-11-2023).]

1985 Fiero GT OCT 11, 08:48 PM
Oh ok, I did not know that, I figured the part looked to flimsy to be a standalone unit, if that is the case it will be better to get a new alternator
1985 Fiero GT OCT 11, 08:54 PM
Something like this good: https://www.rockauto.com/en...5&cc=1249208&pt=2412
Rock auto cheapest option for 1988 Fiero alternator
Patrick OCT 11, 09:10 PM

That would probably be fine. Don't forget to buy the little electrical adapter thingy mentioned at my earlier link.

This is the one I bought for my Formula two years ago. At the time, it was $104(Cdn) total... taxes, delivery etc to my door. Prices have gone up.
theogre OCT 11, 10:42 PM
Before throwing parts....

Iffy Volts are often F'd wiring.

Just the Alt often have wiring problems more so w/ SI & crap Side Plug that is Root Cause of many Alt "problems" because "water" attack the plug & wires under the plastic insulation.

Alt Case is the Ground & iffy Hardware holding the alt to engine can be problems too.

Any iffy Gourds or Power lines can cause same problem as top post.
Just in the engine bay have many "grounds" bolted to Engine, Trans Bell, & Frame that craps out.
85-88 have + box under C500 that often have same problem as SI Alt Side Plug.

See https://web.archive.org/web...cast.net/~fierocave/ wire service & rest of section.

Many Claim CS solved problems like this is missing must install New Side Plug so installing CS parts hinds whatever real cause & often doesn't fix other crap grounds etc.

If the SI is Really Bad, upgrade to CS will help some other things but not others.
See cave Watt Story for Examples.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 10-11-2023).]