We have installed a 3.4 in my son's '87 GT. It runs fairly well, everything seems right on....except the alternator voltage.

When we first fired up the motor, Hunt (my son) was in the driver's seat & I was around back, observing. The engine caught & began to idle. I thought I saw a small single spark shoot from the alternator, but didn't pay it any mind since the engine caught & I was looking more at fuel pressure & looking for leaks.

After letting it warm up I sat in the driver's seat & noticed the voltage was @ 8 volts, way low. I pulsed the throttle to see if the belt was loose & the alternator would engage. Absolutely no response on the guage.

I have checked the belt,good tension. I checked the voltage at the big red wire on the alternator, 12.8 volts (engine off). I checked all electrical connectors, grounds, etc., all looked good. I can tell the engine is running off the battery: cab lights are low & engine idles & sounds like the alternator belt is real loose (all Fiero owners can recognize this condition). There is a steady drain on the battery, & I keep trickle charging it.

Today I replaced the alternator with a good spare I had. Fired up the engine and got 12.8 volts plus at the guage. This lasted about 10 seconds or less, and the guage dropped to 8 volts or less, cab lights dimmed, and no response from the throttle blips, trying to stimulate a loose belt condition again. And that crisp edge of engine idle & throttle response was gone again.

Only thing I can think of is to go over the entire wiring harness again. I'm going to pull the entire engine block grounding stud and clean & replace it (the main one which the battery negative wire runs to) and replace the flat grounding strap that also attaches between it & the passenger side hinge.

Any advice direly appreciated.

you know what? i'm having this exact same problem, although intermittently, in one of my cars. it has a 3.1 in there. there are no shorts. the only thing that i think mine can be, and trust me, i've checked,is the idler/tensioner pulley. i know that mine is slowly, but surely going the way of the dodo. let me know if you figure it out.

What is the voltage at the alt? Should be around 14.4V. You may have a wiring mistake that is killing alts.

quote Originally posted by rube: What is the voltage at the alt? Should be around 14.4V. You may have a wiring mistake that is killing alts.

my guess too, specially since you noticed a 'spark'. Maybe a wiring short somewhere too. With next alt, leave the wiring off and have a voltmeter connected to it. Watch what the voltage does. I think that should show you what the alt is doing. Then if you connect it and it quits youll know. Make sure you disconnect battery when you connect alt wiring.

I have gone though every fiero alternator problem in the book all with working alterntors or as i like to call them known goods :-). Obviously there are 3 wires tot he alternor. ONe main to the battery juction box , one of that to pin one of the plug, and one to the ECM (black) on pin to. It gets it ground from the block. First thing you should note
1 IF you have a good battery you should be able to run the car well for 20-30 mintues on battery power and watch the guages SLOWLY creep down to 8 volts from 12 and shut off. IF this is not the case and your battery is good then you proabably have a short that is makeing the volts drop quickly. Two possiblitys on that... ether the alternor is interally shorting (ie its bad) to ground, OR the more likly possiblty is that the main positve cable to the juction box is shorting or the lead off it to pin one. This cable is predicuallar hard to route and likes to get caudght up in belts and exaust manifolds and the muffler(ive blew a cable all of the above ways in a week) and then preceds to short out intermitinaly or all the time as the car moves.
BEst way to check this is to remove the psotive cable fromt eh jcution box and see if the car last longer before droping to 8 volts. IF it does then youve got a short somewhere AFTER that wire. IF not yopu may have a short on one of the other unfused connections fromt he juction box.

The other posibilty is that that cable is just plain bad. I had one that would work sometimes and not others with 3 different alternors finally i took it in and they moved the cable around while the car was on and the voltage would go up and down accordingly... Cable was bad interally (i picked up from a junkyard replacing a burnt old one and it looked poerfectly good) REplace that cable and check resitse from the termal on the alternor to the postive batttery termal. There shouldnt be very much if any at all. wiggle it and mkae sure this doesnt change. I would buy a new cable form like walmart or womething this way u are sure. Replace the 2 proung connector with a new one if it looks curroded at all. Resplice it. Avaible at any auto parts store in the "HELP!" deparment. This way you mkae sure that is also working good. MAke sure that there is still plastic bettwen the postive termal on the alterntr and the casing. OBviously if that is worn enough that the cable touches the casing youll ground out and bbe in trouble. PM me email me or IM on aim if you have any more probelems or question ive have more ideas and im always glad to help. IVe changed my alternor at least 6 times tryying to hunt down these problems! IT works now though :-)
RATE ME!
ALEX

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Silver 85 GT modified 5 speed
Black 87 GT Getrag 5 speed 7 speaker sound
Black 85 coupe parts car (need any parts?)
88 GT black auto minor wreak in front ON THE WAY! :-) (thanks forum!)
SOLD! Blue 87 coupe

RIP 86 white coupe 49k miles (Unrecalled) Burned to the ground :-(

AIM: (please IM ME LETS TALK. I love to BS about Fieros) IAMKURTDCOBAIN (old sn cant lose it)

EMAIL : Anaverin@juno.com

Check the wires at the starter, make sure that they arn't touching the block. or the little stud that comes from the solinoid.

V/R

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Ed

http://hometown.aol.com/idomy0wnracing

Ok, I just got caught up on the last few posts, and will be back out today to test & try those suggestions.

I did take the first alternator in to town & had it checked. The autoparts store pronounced it "good". I guess that is a relief, and helps narrow the search somewhat.

With the multimeter, I read 12.8 volts across the battery with ignition off. Also read same voltage at alternator & battery junction block.

I read fairly low resistance from alternator to bat. junc. block, but will "unharness" that wire, inspect it, and maybe replace it as suggested.

I read fairly low resistance across the gronding strap from engine block to hood hinge.

I checked all fuses in the fuse block, they were good.

I tried running engine again. Before, I had said it indicated 8 volts. That is wrong, 8 is down under the red zone. The needle is resting about on 11 or 12 (somewhere above the red zone and below the middle mark on the guage). That is the same voltage I read across the battery, at the alternator, and at the bat. junc. box when the engine is running.

I wish I lived in Florida right now, it's cold out there.

PROBLEM SOLVED
:> :>

You'll laugh when you hear what it was. We had detailed & painted almost everything on the engine. The alternator bracket had three coats of por15 on it, looks real nice.

Turns out the por15 had isolated the case from grounding thru the bolts. I ran a ground strap from the engine block to the alternator case, and presto, 15.7 volts.

The sun began to shine again at that moment, and I knew that deep down inside, I really do like working on Fiero's. We finally took it out for a brief road test and it was sweet.

I can't tell you guys what I've been thru the last few days, and how intimate I've become with the charging system. Thanks a million for your advice and guidance!

My 'ol Daddy allways said that the best advice you give is that which you learned about the hard way. So, if you ever paint an engine bracket, think twice about the electrical grounding of whatever it is holding up.