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.
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.
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
------------------ "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).]
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).]
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).]
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.
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.
------------------ 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)
Yes, I have read your articles, but like I said, the wiring on this car is quite good, I'm sure it is possible that there are some problems, could very well be the sensor for the alternator, but what I have seen indicates that the overall wiring is quite good, but from my symptoms if you can point me at a specific location to remove and clean connections and test voltages to rule out a specific wiring issue, that would help, even if it is wiring, it will be something intermittent, although it is completely random, it can happen when I am driving at 80 on a somewhat bumpy road and it can happen while sitting still and idling, and anything in between, if it were a physical wiring issue I would expect it to have some correlation to a physical cause, either a specific kind of bump, specific rpm, specific temperature, specific speed, etc. The symptoms are like the alternator is being turned off by something, but what is puzzling is why it always turns back on, and why it is only off for a few minutes at a time, seemingly randomly. Thanks.
Originally posted by 1985 Fiero GT: Yes, I have read your articles, but like I said, the wiring on this car is quite good, I'm sure it is possible that there are some problems, could very well be the sensor for the alternator, but what I have seen indicates that the overall wiring is quite good, but from my symptoms if you can point me at a specific location to remove and clean connections and test voltages to rule out a specific wiring issue, that would help, even if it is wiring, it will be something intermittent, although it is completely random, it can happen when I am driving at 80 on a somewhat bumpy road and it can happen while sitting still and idling, and anything in between, if it were a physical wiring issue I would expect it to have some correlation to a physical cause, either a specific kind of bump, specific rpm, specific temperature, specific speed, etc. The symptoms are like the alternator is being turned off by something, but what is puzzling is why it always turns back on, and why it is only off for a few minutes at a time, seemingly randomly. Thanks.
You can upgrade to CS & Still have same problem because wasn't a bad SI.
Iffy "Grounds" can affect engine running because not all are Grounds like Tan "Ground" is 1 side of "1 wire" O2 sensor for ECM.
Iffy "Battery" light & related parts in the dash, Iffy Alt Side Plug, & just wire for that light will cause problems like that. Other wiring problems can do that too.
Don't go but "how they look." Disconnect, Clean, & lube w/ Brake or Silicone Grease all "grounds" bolted to engine, wires to Alt & + Box under C500. As you check, look/feel wires at ends... Water damage under insulation can make wires swell or even break there & feel way different then good crimp ends.
See cave, Alt Sense telling what the side plug does.
I would even carefully "unbolt" & unplug C500 & plug it in a few times. Don't remove the Bulb Grease that "waterproof" it. That can make the connections to get better metal to metal as wipe away/thru "rust" in them like The Battery Light goes thru.
Cleaning Engine Grounds often needs "Dremell" w/ wire wheel/disk, cup, etc to clean the "stud" many attach to. Many "Dremell" kits steel wire wheel but can buy cups & other shapes. Don't need SS or Brass wheels for this job. That often makes quick work of cleaning the studs even if can reach all of it. Don't run "dremell" @ max speed w/ any wire brush. Running over rev just ruins them & fly off wires often find your skin, worse Eyes. Don't need the threads total clean but bolt head face @ base should be bright metal.
I recently had "Ground" problems because missed cleaning 1 Stud on Trans Bell.... The Ends are good & lubed from old engine but missed cleaning that stud cause weird Codes for ECM & Ignition problems because DIS Power Ground uses same stud. And this happened several years after replacing the engine. I may have clean that stud but forgot to grease it to keep out "water."
Go buy Permatex Green Brake Grease. Won't run or dry like most Silicone grease in the engine bay.
What Ogre says about grounds is so true. However, I went up to your original message and I think that the alternator is not pushing out what it should? Some of the other replies concerning the state of the alternator and/or it's regulator should be looked into. An alternator here in europe will push out 14.2V. Anything less, like your 13.6V would seem a little low? Even at idle, it should try to stay close to 14V (13.8, 13.9, etc...) Droping off to battery voltage at idle or when at low speeds is in my opinon a bad sign.
------------------ "Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero https://youtu.be/hUzOAeyWLfM
Yes it hits 14 anything very rarely, and only for a few seconds before it goes back to about 13.6, like I said it is the lowest spec alternator a v6 could come with, 66 amps, so it could be that it can't generate enough volts. I know engine off battery charge is around 12v, so it is definitely doing something, maybe not enough though.
Well that's not good. Try finding a cheap one on RockAuto, Ebay, etc... I changed my alternator a couple of months ago with a RockAuto special clearance sale. Only cost arround 30€ + shipping. Works fine👍😉
------------------ "Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero https://youtu.be/hUzOAeyWLfM
What Ogre says about grounds is so true. However, I went up to your original message and I think that the alternator is not pushing out what it should? Some of the other replies concerning the state of the alternator and/or it's regulator should be looked into. An alternator here in europe will push out 14.2V. Anything less, like your 13.6V would seem a little low? Even at idle, it should try to stay close to 14V (13.8, 13.9, etc...) Droping off to battery voltage at idle or when at low speeds is in my opinon a bad sign.
Depends exactly where tested... @ the alt or battery should be nearly same volts. But The rest of car... Anything Have Many Connections & each one add a voltage drop. Worse Often have wiring problems on top of that.
So Volts across say HL Bulb is Often 1 to 3 volts < Volts @ the battery.
Even when Alt is 100% Good, Anything Wrong w/ Sense Wiring & Side Plug means Volts are higher or lower then Spec. Is Why GM for about 85 model year shortened the sense wire to jumps directly to alt output. & all models not just Fiero.
When have SI or others w/ crap plugs, Just Touching the plug can make volts to change or shut off. CS w/ Locking Metripack Plug doesn't have that problem because can't move & is Weather Resistant to keep out "water."
Ok. My volts are measured by the volt meter which is wired into the ignition switched power and ground on the rear defrost connector, voltage across my while car is relatively stable, like I said the wiring seems good, probably just one connector somewhere that has a problem, I just did a half hour drive with no accessories on, in cool weather and the alternator didn't cut out, voltage started around 12v engine off, 14.3 volts just started up, then dropped to an average of 13.6, jumping between 13.3 and 14, occasionally.
Do you have a multimeter? You should check what the battery is getting. If it's not 14.1V , 14.2V or near then you need to check the output at the alternator +ve wire. Ditto, if it's not above 14V, then there's a problem. Less than 14.1 or 14.2V, the alternator or it's regulator is toast.
------------------ "Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero https://youtu.be/hUzOAeyWLfM
[This message has been edited by Frenchrafe (edited 10-12-2023).]
Ok, I will check that when I get home, will also compare battery direct readings to my cabin voltmeter to see how much of a voltage drop there is between the battery and the rear defrost switch
Do you have a multimeter? You should check what the battery is getting. If it's not 14.1V , 14.2V or near then you need to check the output at the alternator +ve wire.
On my vehicles, (Fieros and a Subie), 14.6 volts is what my alternator is feeding my battery after the engine starts. A fully charged battery should be just under 12.6 volts.
I also wanted to add, that prior to replacing my alternator two years ago... the alternator would intermittently stop charging and then start charging again. I couldn't trust it. I took it apart to make sure the brushes were making contact etc, but I couldn't visually find any problem. Replacement of the alternator solved the problem.
[This message has been edited by Patrick (edited 10-12-2023).]
Ok, I will check that when I get home, will also compare battery direct readings to my cabin voltmeter to see how much of a voltage drop there is between the battery and the rear defrost switch
Ok, starting Fiero with multimeter in battery directly, multimeter reads 14.0, volt gauge in cabin reads 13.8, but that is immediately after starting it with no accessories on. After driving it, like I said volt gauge settled to an average of 13.6, which would theoretically put battery voltage at 13.8, still to low, and that is the average, with it varying as low as 13.2 on the gauge (theoretical 13.4 battery voltage) and then the times that the alternator "stops" charging, voltage starts at 11.8 gauge, then slowly drops until it kicks back in, back up to 13.6 gauge
Voltage at the alternator is within .01v of voltage at battery when engine is off, 12.42 battery, 12.41/2 alternator, and this time I started it voltage was 14.21v to 14.25v at alternator and battery (voltage varied over the time, wouldn't remain constant enough to check between alternator and battery) for the minute or so I had it on,
On my 88 V6 the thing that makes the voltage drop is when I first turn on the AC, then it jumps back up. I don't know if it jumps back to what it says before turning AC on because I've never looked at it that close. IMO, if it says 13 1/2 or more I'm not concerned. BTW, I have factory volt meter. In fact I wouldn't be concerned if it said 13 or more because who knows how accurate the factory gauge is given the accuracy of the fuel gauge for example. Having said that, my gauge the other day started registering a little over 12V and the idiot light comes on and stays on, so I'm thinking new alternator time. I don't know what all the conversation about different ALT is about, I don't know what the abbreveations you are using means.
Long story short, 85/86 fiero's have one, older, worse alternator, 87/88 has The cs130, better newer, etc. Newer alternator can be put in older car, with a simple cable adapter from Rodney
