88 with an L67 swap. I have a .64A drain. Takes about 8-10 hours to drain the battery. After following advice from another thread I hooked up a voltmeter and started pulling fuses under the dash. Pulled all of them and still have a .64A draw somewhere. Check the alternator and it comes back good with a good diode. The auto parts store asked if it had been replaced recently it was working so well. So now I'm at a loss. Fusible links would be next to check? Anything else I should look for? Maybe a *cringe* headlight module?
-Mike

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Disconnect the alternator wiring completely, if the drain stops then the diode trio inside it is blown. Electricity is really simple in the Fiero. Other than the alternator the only other devices connected full time to power are the radio and the ECM. IIRC, the radio memory circuit is through a fuse but the ECM memory is through a fusible link.

JazzMan

Yep, try to unplug the alternator completely as stated. Also try unplugging the ECM, maybe something there is wired wrong? Anything aftermarket like stereo equipment or alarms? When did the draw first start?

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88 Coupe: Modded 4.9L V8 5 speed
84 Coupe: 4 Cyl 4 speed
www.geocities.com/fast88fiero

Like JazzMan says, the alternator is a likely suspect. The headlight module is also powered on all the time through fusible links but the connectors can be easily removed to break the circuit.

[This message has been edited by spark1 (edited 02-22-2009).]

quote Originally posted by JazzMan: Disconnect the alternator wiring completely, if the drain stops then the diode trio inside it is blown. Electricity is really simple in the Fiero. Other than the alternator the only other devices connected full time to power are the radio and the ECM. IIRC, the radio memory circuit is through a fuse but the ECM memory is through a fusible link. JazzMan

What about that huge wire going from the positive terminal to the starter...? I know, it's highly unlikely since it's controlled by the solenoid, but I still thought I'd keep that in the loop of possibles...
-Paul

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Journal of a concept: http://southeastfieros.com >>> Build Thread >>> Parts thread (for project funding)

Sometime last month is when the drain started and it was just to cold/snowy to bother trying to find it. I guess I'll try to find some time between working on computers this afternoon to unhook the alternator and check it again. Thanks guys a + to all that don't already have one from me. I'll report back soon as I can get that stuff checked

When a BMW comes in the shop with a battery drain, the first thing we do is unplug the alternator....I think it is the most common problem with battery drains that I see.
Dave

Autozone has not done anything but disapoint me lately. Glad you found your problem. I had a drain on my car that ended up being a bad headlight motor but took me a few days and many jump starts to figure it out!

Jason

Welp pulled the alternator put in a new one and the drain dropped to .58A but its still there Now where should I start looking?

You're Lucky your draw was so low, My replacement alt from autozone put a 4 amp load on my battery!
It took about 6 months of on / off troubleshooting to figure that out...

Sounds like another bad alternator (the new alternator is plugged in when it's reading 0.58 Amps, correct?). Unplug it and see if it drops back to 0.02 (0.02, or 20mA, is well below the acceptable 0.035). I got an AC Delco remanufactured 105A CS unit from Rock Auto, has worked great for years.

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1984 Fiero SE

Don't overlook the headlight module. The 87-88 module and headlight motors are not prone to failure and battery drains, but it's possible since they are powered on at all times.

quote Originally posted by Silentassassin185: Welp pulled the alternator put in a new one and the drain dropped to .58A but its still there Now where should I start looking?

Do you still get that drain when the control connector is disconnected from the back but the large red charge wire is connected to the bolt?

TK - I'm not sure I'm at work right now but I'll check it tomorrow after class.

jscott - That's on my list of suspects. Something else that should get checked tomorrow.

quote Originally posted by Silentassassin185: Just checked this and the drain disappears when I disconnect this. So does that mean this alternator is junk too?

With the key off, measure the voltages on the connector.

Are you using the Fiero alternator or the one from the L67?

TK - will check that after work tommorow morning if its not snowing >_<

spark1 - the L67 alternator

I think the regulators on the two types are different. Ogre mentions that in his Cave. The 88 Fiero uses the "I" (ignition) lead which is the "F" (field) lead on other CS alternators. He mentions that this can cause a problem and that the "I" lead shouldn't be connected if a non-Fiero CS is used. Don't know if this is what's causing your problem but it's another possibility.

quote Originally posted by TK: With the key off, measure the voltages on the connector.

Ok so we got a few inches of snow today and by the time it stopped I went out and couldn't see what i was doing without a light and couldn't do it all, didn't have enough hands. However a quick question. On the connection which two should I be testing? I have a picture on my phone of the connector I can upload tomorrow if need be. But the basic shape is like this.

code:

---

__________
|P|L|F|S|

---

I'm assuming I'm checking the two smaller connections. The first(P) is empty and the last(S) is a bit larger then the smaller two in the middle.


"P" Terminal (Phase Connection) - This terminal sends a signal to a relay, frequency sensing tachometer, or computer indicating alternator speed. This terminal may not be used - this is normal.
"L" Terminal (Charge Light) - This terminal is fed from the ignition through the charge light on the dash. This connection turns the alternator "on". Without a signal to turn "on", the alternator will not charge. However the "I" terminal may be used to turn this alternator "on", as described, instead of the "L" terminal. Please note that if there is a connection on the "I" terminal there will be NO connection on the "L" terminal.
"F" Terminal (Field Monitor) - This terminal sends a signal to the computer telling it how much field current is flowing (therefore the computer knows how hard the alternator is working). This terminal is not always used AND can only be used if the alternator is turned on by the "L" terminal.
"S" Terminal (Battery Sense Connection) - This terminal is larger than the others and provides the alternator with a precise battery voltage reading however, this connection may not used. When not used, the alternator will automatically sense battery voltage at the battery post.

:edit: Did some searching and so far all I can tell about the connector is what each terminal is lettered. What are they and how exactly do I check them?
:edit2: for more stuff

[This message has been edited by Silentassassin185 (edited 03-01-2009).]

bump

Here is a comparison of the two alternator types; the Fiero is on the right. Since the drain current reduces when the regulator plug is pulled, current must be flowing in one of the circuits (L, F or S).

Bump from the dead. Life calmed down enough to dig back into this and the drain is in the "L" terminal. Any idea as to what would cause this?

quote Originally posted by Silentassassin185: Bump from the dead. Life calmed down enough to dig back into this and the drain is in the "L" terminal. Any idea as to what would cause this?

I have read through this post with some vested interest as mine is showing similar symptoms. (too many other problems with the car to address this right now)... Alternators generate A/C, which is no good to a car. The "Rectifier bridge" in your schematic is what converts the A/C to D/C. The bridge is made of diodes, which only allow electricity to flow in one direction. If one of the diodes blows, it could allow a drain. New alternators are rarely new. Most are rebuilds. If the alternator you bought bench tested okay, they wouldn't have replaced the rectifier. Higher dollar models get new parts without bothering with bench testing. Autozone often sells two parts: the good stuff (Usually in nice packaging), and the generic (Plain white box). It is possible you got a bad alternator out of the box. Your voltage difference from one alt to the other makes me suspect this. If the alternator was identical and not the problem, in theory the drain should have been identical. If you still have the receipt for the alt, I would exchange it. It will either fix the problem or eliminate the alternator from the equation. I would also try some of the suggestions offered on other possible drains... When you pulled fuses, did you pull the circuit breakers also? (Small silver boxes in the fuse box)...

When I get around to diagnosing mine, if you still haven't solved this I will keep you posted on what I find. (My son and I are working on a project car for him, but school just started so the car is weekends only now).

I pulled everything when I pulled the fuses. Is there any way to test for a bad diode? The old alternator tested fine at Autozone and Oriellys both but we replaced it anyway expecting a bad diode and still had the drain. Been trying to find more information about the "L" Terminal but with school plus work I haven't had much time and even less luck finding anything when I have the time.

It looks like the schematic on the left (L67?) utilizes a resistor at the idiot light (probably built into the cluster).
The fiero on the right does not,it has the resistor built into the alternator.
Maybe adding the resistor..?

quote Originally posted by Silentassassin185: I pulled everything when I pulled the fuses. Is there any way to test for a bad diode? The old alternator tested fine at Autozone and Oriellys both but we replaced it anyway expecting a bad diode and still had the drain. Been trying to find more information about the "L" Terminal but with school plus work I haven't had much time and even less luck finding anything when I have the time.

Testing a diode by itself is easy... It's an electrical check valve. Voltage will flow in one direction, but not the other. When these diodes are wired together in a bridge rectifier, they create a passage for A/C to become D/C. The problem with testing them is you would need to pull the alternator apart, and test each one independently. I don't know of any other means of testing them.

Try disconnecting other components. Physically disconnect the headlight motors, ECM, and then pull the fuses. If you're still reading a draw, then disconnect the Alternator. If the drop goes away, I'd say it must be the alt. (With the radio fuse and ECM disconnected, your current should go to zero. The .02 Amps you saw is probably the constant hot wire to the stereo. Also... Pull the connector to the gauge pod. (First car I've ever owned with both a gauge and a dummy light...)

-Also...Like FieroMaster88 asked,do you have any aftermarket accessories? If you aren't the original owner I'd look for signs of aftermarket equipment. I had a Thunderbird with a similar problem. When I finally tore it apart in an effort to find what was causing it, I found an aftermarket security system hidden in the dash All other components had been removed, but they left the module. The system wasn't installed correctly, and was pulling about an amp.

I guess I might pull the alternator out and have it tested but can't afford $200+ for another new alternator and they wont replace this one if it tests ok.

quote Originally posted by DefEddie: It looks like the schematic on the left (L67?) utilizes a resistor at the idiot light (probably built into the cluster). The fiero on the right does not,it has the resistor built into the alternator. Maybe adding the resistor..?

This is on your L terminal,have you tried adding the resistor?
The resistor look to be simulating a load across the circuit.
If you installed the 3800 alternator then it's expecting the resistor in the guage,though your old one(guage,alt) had the resistor built into the alternator.
You could have a short to ground on the L circuit also pulling voltage.

And never test an alternator off the vehicle,the testers we have at autozone suck.
Same with starters,these things operate normally with an electrical or mechanical load.
Your testing without the load applied,most will pass everytime unless it's a diode or regulator.
Even then they aren't real accurate,always test on the vehicle whenever possible.

Is there a way to check for faulty diodes on the alternator? I am thinking that a small battery hooked up to the alternator (away from the car), or measure for resistance or something. I would have to see the car in person to help. So you need to give me the car Mike.

Just to confuse Mike more than needed, here is a wiring diagram that has nothing to do with this. Anyone scanning the page and not reading should also be confused.



Brad

I haven't drove it in a couple of weeks so I'm sure the battery is probably dead but I'm going to try to start it this weekend and cruise up to autozone and test it in the car and see what happens. Its supposed to rain all weekend so I can't pull the alternator out til I get some decent weather.

quote Originally posted by Silentassassin185: ... the drain is in the "L" terminal. Any idea as to what would cause this?

Just a minute! There's probably nothing wrong with your alternator. The only source of power to the "L" terminal is through the ignition switch. If your car is wired correctly, it should be impossible for current to flow into the "L" terminal with the ignition switched off.

First check: As TK suggested way back in February, disconnect the regulator plug at the alternator and check the voltages present on the pins. With the ignition switch off, is there still +12 volts at the "L" terminal of the plug? If yes, continue below. If no, there is probably a wiring problem at the plug itself. Does the "L" wire on the plug actually match the correct "L" position on the alternator? Not all alternators are the same.

Second check: You need to check the entire circuit from the ignition switch to the "L" terminal. Is the "Alt" lamp on constantly, even when the ignition switch is off? If yes, then either 1) the ignition switch is bad, or 2) there is a wiring problem between the ignition switch and the lamp. If no, then either 1) the lamp is burned out or missing (replace it and check again), or 2) there is a wiring problem between the "Alt" lamp and the alternator.

Let us know what you find.

[This message has been edited by Marvin McInnis (edited 09-04-2009).]

quote Originally posted by Marvin McInnis: First check: As TK suggested way back in February, disconnect the regulator plug at the alternator and check the voltages present on the pins. With the ignition switch off, is there still +12 volts at the "L" terminal of the plug? If yes, continue below. If no, there is probably a wiring problem at the plug itself. Does the "L" wire on the plug actually match the correct "L" position on the alternator? Not all alternators are the same.

There a right or wrong way to test the pins? I'm not great with wiring and electronics. Prefer the mechanical side of things.

quote Second check: You need to check the entire circuit from the ignition switch to the "L" terminal. Is the "Alt" lamp on constantly, even when the ignition switch is off? If yes, then either 1) the ignition switch is bad, or 2) there is a wiring problem between the ignition switch and the lamp. If no, then either 1) the lamp is burned out or missing (replace it and check again), or 2) there is a wiring problem between the "Alt" lamp and the alternator. Let us know what you find.

It rained all day today and when it finally quit I was running errands, now I'm at work. So I'm hoping for a break in the rain this weekend to try and get this sorted out. A + for you Marvin.

quote Originally posted by Silentassassin185: Stuck the voltmeter to ~V and ...

It appears that you set the meter to measure AC volts rather than DC. That won't work. With the meter set to DC and the 20 volt range, you should measure 0 volts between the "L" terminal on the plug and ground when the ignition switch is off, and approximately 12 volts when the ignition switch is on.

At this point my best suggestion is that you find someone near you who already knows a little about electric circuits and can provide you some hands-on help. Otherwise, troubleshooting your problem is likely to be an exercise in frustration both for you and for those of us who are trying to help you.

DOH! That's why I had asked earlier if there was a right/wrong way of doing it. Figured I had a 50/50 shot. Ran out and put it to DC (can't draw the three dots with the line over the top) and checked it. nothing with the ignition off about 3v with it on but thats because the battery is dead again (its no longer holding a charge) So i'll replace it and continue on.

Trying to find some local help but with full time job plus school and remodeling a house my free time is limited at best. Besides frustration is a common occurrence with Fieros right?

quote Originally posted by Silentassassin185: 88 with an L67 swap. I have a .64A drain. Takes about 8-10 hours to drain the battery. After following advice from another thread I hooked up a voltmeter and started pulling fuses under the dash. Pulled all of them and still have a .64A draw somewhere. Check the alternator and it comes back good with a good diode. The auto parts store asked if it had been replaced recently it was working so well. So now I'm at a loss. Fusible links would be next to check? Anything else I should look for? Maybe a *cringe* headlight module? -Mike

This may sound ridiculous but it happened to my '88 GT. How's your trunk light switch? If your trunk light switch isn't aligned correctly (or the mount hole is cracked) the light will stay on even after you shut the deck lid and you'd never know. Just like you described, my batt would be drained overnight. So, I took the bulb out til I could fix the problem.

A possibility

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=-Eric the Dread

1988 Fiero GT 2.8L V6
2001 Grand Prix GTP SC3.8L V6