By the time the car warms up, I turn on the stereo, the headlights, the A/C to max, and step on the brake, I'm down to 11.8V at idle and the stereo is cutting out. There should be more than enough power available, since I installed an upgraded alternator (200 amp) an oversize 1000 CCA battery, and the extra ground-strap trick, but these had no effect on the low voltage situation. I've also read Ogre's article on alternators, but I'm not finding the answers to my questions. First of all, why is this power drain drawing volts, instead of amps? Second, what else can I do about it? I've had lengthy arguments with alternator "experts" who tell me that this kind of voltage drop after warmup and under heavy load is symptomatic of failing diodes in the alt, but I just replaced it. What else is going on?

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do you have relays for the aftermarket accessories? The relay will handle the load better than running wires to the fusebox. I found by properly rewiring a lot of the Fiero, my loaded voltage prior was around 12.8 volts and after is about 13.9. With the load off I am at 14.2 on the stock Fiero alternator.
Dave
ps I also found that on my V8 the alternator spins slow at idle and causes charging issues. I bumped up my idle 50rpms and it helped with both the charging system and the overlapping camshaft.
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1999 Mercedes ML430, 450hp 1987 Fiero GT, 1986 Fiero SE-soon to be 3800, certified master technician
www.njautobahn.com

[This message has been edited by bmwguru (edited 08-01-2007).]

Can you elaborate on what you mean by "properly rewiring"?

quote Originally posted by crazyd: Can you elaborate on what you mean by "properly rewiring"?

Well, I am running aftermarket headlights, stereo, electric water pump, electric brakes, electric fuel pump, and a MSD igition system. All at the same time can create a large load on the alternator. First thing I did was increase the size of the battery cables. Second, make sure every part of the engine and frame has a good ground from front to rear. Add an auxiliary fusebox like the VW Jetta IV to run the stuff up front with their own relays and independent ground wire to the common ground. Make sure the wiring isn't too small or too long to meet the demand. Replace the wiring at the alternator with a new connector...the GM one will probably be corroded up by now. Solder all wires. No butt connectors or scotch locks are used in my wiring. And in the rear, a relay panel set up for all the stuff in the engine compartment. The only original wire from 1987 in my engine bay is the one for the VSS....other than that it is all new wiring.
Dave

are you running fiero stores underdrive pullys?, i am on my 3.4 conversion and at idle with AC/radio/headlights/ and sometimes wipers...its reading like 9.8 volts. with everything off it reads at idle it reads 12.9, give it not even 100rpm and it jumps to 11.9ish and 13.8...ive allways thought mine was to low..but again im running the usless POS underdrive system from the FS

I have a GM AC Delco heavy duty alternator (130amp) that I bought and upgraded the regulator to the truck regulator. (It's the one they use in the towing package trucks.) There was an article in Car Audio Magazine about GM regulators which had part numbers. I'll see if I can locate it and scan in the info.
Anyhow, This allows the alternator to start to charge as low as 600 rpm. The Fiero alternator seems to charge at around 750/800 rpm.
Swapping the regulators is easy to install.
On my car it runs at about 13.9V with the stereo and lights on but it will drop as low as 13.2V with all the accessories on (fan, driving lights, high beams, rear window defog, Hazard lights flashing, and brake lights). I do not have A/C on my car.) and the front cooling fan on. With everything off and the engine idling I get 14.1V.

I also upgraded the wire on the alternator to a 8 awg high current wire rather than the stock 10 awg wire. This seems to help the most especially when you have the battery front mounted in the car.
I should also note that I am using an Optima yellow battery which seems to reduce the charge up time. Before I upgraded the wire I use to get the headlights to flicker and the volt meter would move to the beat of the music when the stereo was cranked way up at idle, now the volt meter barely moves and the lights don't flicker.

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Happiness isn't around the corner...
Happiness IS the corner.
ZZ4 Powered !!

[This message has been edited by Oreif (edited 08-01-2007).]

What type of alternator are you running? I've had problems with the ol' SI series charging at idle. I've never had issues with CS series alternators charging at idle.

At what speed does your engine idle?
Ive got the CS on my 3.4. When I put the underdrive pulleys on, I had to bump up the idle in my chip by 100-150 RPM or so. As long as I keep it over ~900, it's all good. If it's really hot, it needs 1000 RPM, I think.
Of course, it all depends on your pulley size.

With my 86 gt with a CS upgrade and a wire upgrade I can get almost 17v at idle and thats with no load but under max load (ac,fan, coil blower, all lights, hazards, 1200&1800 watt amps, and brakes on) it doesn't drop below 14.2 volts and goes back up to 17v at 3000rpm. I know this will damage batterys but personally it doesn't bother me and I would rather have to much than not enough in the alternator area. I had a customer who had a stereo system in the 9000 watt area and he couldn't get his volume to 40% because it would suck so much juice it would stall the car (200amp alt, 2xoptima yellow top, 5 farad capacitor, big 3 wire upgrade) so feel luck yours doesn't do that because he had like 15grand into a competition stereo and couldn't use it for more than 15min.

I'm not running an underdrive pulley - those are a really bad idea, especially in Fieros - but the 200amp CS-130 alt I just put in did come with an overdrive pulley to go from 90amp idle charge to 105amp, which I would try but I don't think I've got an amp problem. Sounds like what I really need to do is upgrade the BAT wire on the alt with a fattie 4ga. I don't need 17V, but I'd be okay with 13.5 at full load. At least the windows would work. The battery puts out 12.8, so if I'm going below that then I'm undercharging.

As for the guy with a 15 grand stereo who could only use it for 15 minutes, you could point out that the Bugatti Veyron, which will do 253mph, will only do it for 12 minutes until the gas tank runs dry. And that costs 1.5 mil.

[This message has been edited by crazyd (edited 08-02-2007).]

One of the biggest problems with old cars... is the wiring gets old too
I have replaced various circuits here and there and the first thing Ive noticed
is a voltage increase. IE power windows.... mine were very slow... until
I had to replace the wringing and OMG fast windows. I discovered this
when stripping my 84 and had to put the windows up for safety reasons.
I had already yanked off the door panels so i cut the connector and hooked
up a fresh battery to put them up. They went up fast for the first time in 8 yrs.

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87 Fiero GT 5sp with Vortec L35 4300 Turbocharged V6
Bully Stage 2 clutch
Syclone intake manifold and engine management with Moates adapter and chip burner
Air/water intercooler and Devil's Own progressive water/alky injection
50lb injectors, 3 bar map sensor, Walboro fuel pump and Jabasco Intercooler pump
LM1 wideband on custom manifolds and 3" stainless exhaust system
T31/T04B S4 turbo with a Super T61 in the box
S10 caliper conversion.
Murphy's Constant Matter will be damaged in direct proportion to its value
Murphy's Law of Thermodynamics Things get worse under pressure.
Arthur C. Clarke "Any significantly advanced technology is indistinguishable from magic"

When you got your new alternator, did it come with a spec label? my replacement did, and it specs the 'turn on rpm', and the rpm for the full 120 amp output. Your alternator may not put out until the motor hits about 1200 rpm, normal for cold idle but not for hot.
Orief's post may lead you to the right area, if you can find a lower rpm turn on regulator, you may have your problem solved.

I had done an upgrade on my boat on one motor to a 100 amp self contained alt from the 30 amp stock one, the guy I deal with told me flat out, it would not even turn on til it hit 1500 rpm, then would be fine tho lowered output at idle (600 rpm). if I watch my guage, it will see it kick in at almost exactly 1500, and will never even flinch with a load if motor is over 1200.

I ran a new 4ga wire from the alternator to the C500 junction, and voltage only goes as low as 12.2 volts (tested on the cig. lighter socket in the interior, it's about 12.5 in the engine compartment) with max A/C, headlights, brake lights, and audio. That's a significant improvement. I am going to try a bigger engine block ground next and see if that brings me up some more.

You may be seeing normal voltages. Here's some info from GM that may help. (Could be titled "It Ain't Necessarily So")

quote May 2002 Volume 4, No. 5 Tech Link A monthly publication for GM Dealership Service Professionals Generator Operation and Troubleshooting Over the past few model years, GM has improved generator reliability by installing larger generator bearings, higher temperature greases, and high temperature press-fit diodes across all generator lines. However, while these design changes have improved generator warranty over-all, the percentage of good generator replacements has increased. A recently completed analysis of generators that were replaced shows that roughly half were functioning properly. This raises concerns with proper on-vehicle generator diagnosis. Generator Operation The generator's purpose is to provide electrical power and maintain the battery voltage at the proper level. When electrical loads are switched on, the generator senses this change and increases its output current(amperage) to maintain the proper voltage, until maximum generator output is reached. Electrical loads in excess of generator capability will cause the system voltage to drop below normal. Example: a generator is heavily loaded (summer city traffic) and is attempting to recharge a discharged battery. Generator maximum output increases with engine speed, and typically at low idle speed the generator output capability can be exceeded. Troubleshooting When measuring generator output amperage, make sure you are measuring DC amps in the cable attached to the generator B+ stud and that the current probe is fully closed. Do not measure generator current at the battery. Also make sure your voltage measurement is correct and that the meter is operating properly. Q: What battery voltage level is proper, or normal? A: The generator senses underhood temperature and adjusts the voltage level for proper battery charging. A warm battery will accept a charge more readily, so at higher temperatures, the generator voltage level is lower to avoid overcharging and excessive use of battery water. A higher voltage is needed to charge a cold battery. Normally, battery voltage ranges between 12.0 and 16.0 volts, depending on temperature and load. At engine idle with a fully charged battery and all other electrical loads switched off, the battery voltage should be 13.0 V or greater. At engine idle with a fully charged battery and all electrical loads switched on, the battery voltage can be as low as 12.0 V. Q: If the battery voltage is below 12.0 V, is the generator bad? A: Not necessarily. A discharged battery, and/or high demand for power could mean a low voltage level even though the generator is good and is at maximum output. Also, be sure you are measuring DC volts and not AC. Q: So, then, is the battery bad? A: Not necessarily. If the battery is discharged, and/or if electrical loads are high, the battery voltage could be below the proper level even though the battery and generator are both good. Example: at idle with A/C and other loads operating, the generator may not be able to keep up with demand, so the remaining power comes from the battery. As the battery runs down, the voltage will continue to drop. By raising engine speed, the generator can provide greater out put to restore system voltage. If the battery voltage is below 12.0 V, the generator and battery should be tested independently, following the manufacturer's recommended procedure. Q: If a generator has low or no output current, is it a bad generator? A: Not necessarily. If the battery voltage level is proper for that temperature, the generator will reduce output. Example: the battery has just been charged and is at full voltage when re-installed in the vehicle. If a no-output condition is observed, check the input connection, output connection, and/or presence of a generator turn-on signal. Q: What if the battery voltage is below 12.0V and there is no output from the generator? A: Disconnect and reconnect the multi-pin connector at the generator. The generator could be good, but not getting a good multi-pin connection. In this case, changing the generator may solve the problem, but only because a good connection was made when the new part was installed, not because the removed generator was bad. Q: What if everything seems OK but the generator has very low current output? A: Apply a test load, or turn on the lights, heater blower, rear defroster, etc., and see if the generator output goes up when the demand for electrical power goes up. Try raising the RPM a little. Check all wiring, electrical connections and belt tension. Q: What if the generator current output is intermittent -- high then low amperage? A: Check for an intermittent load. If the A/C, defroster, or climate control are on, the A/C clutch and/or the blower could be kicking in and out, changing the demand, which would cause generator output to fluctuate. Check all connections thoroughly. If vibrations cause any connection to be intermittent, the generator output could fluctuate. Wiggle the wires. One or more of them could be broken inside the insulation. Q: What if the battery voltage is too high, over 16 volts? A: Make sure you are measuring DC voltage and not something else. Check all generator and battery connections, especially if the vehicle is wired with an external battery voltage sense lead through the multi-pin connector. Excess resistance in the sense circuit can fool the generator into overcharging even though it is a good generator. Q: If the battery was discharged, but then checks good after charging, the generator must be bad, right? A: Not necessarily. Maybe the owner just left the dome light on all weekend, or there may be some other power drain due to an electrical problem in the vehicle (see Parasitic Drain, April 2002 Tech Link). This would discharge the battery even though the generator and battery are both good. Occasionally, a battery will become discharged due to the driving pattern of the owner. If the owner takes many short trips every day, over a period of time the battery charge may drop low enough that it will be unable to start the vehicle. Once the battery has been recharged, perform a test of the generator, following the manufacturer’s recommended procedure. Q: If I replace the generator and the output of the new one is higher than the old one, the old one must have been bad, right? A: Not necessarily. The old one was most likely warm. A cool generator will always have a higher output than a warm one until it to warms up. Noises Because the generator has a magnetic field inside which rotates with engine RPM, a magnetic whine can often be heard coming from the generator. Some magnetic noise is considered normal. When trying to determine if a noise is excessive, compare the suspect vehicle to another vehicle of the same type. Noises are difficult to diagnose. There are many devices under the hood that can produce noise similar to that of the generator, such as the power steering pump, fuel pump, fuel regulator, air conditioner, idler pulley, etc. The Technical Assistance Center might be of help and can offer tips about noise issues with particular types of vehicles. Thanks to Rob Rice and Tom Radomski