HELP! 86'Firebird 2.8 won't charge more than 12V

My Son swaped a bone yard 85 camaro 2.8v6 into an 86 Firebird. Runs great for about 10 20 miniutes, untill volts drop down, down down till she runs out of battery! New Battery- New Alt (bench tested at 15V twice) Voltmeter on dash says it starts up at 12V. Battery checks the same 12V Big terminal on Alt check same 12V

All three points check the same readings, even as the volts start droping down to about 7-8 volts. As it goes down you have about

2minites to compair & check points till she's dead.

Charge Batt & away we go again for another 10-20 minites

Checked & cleaned as many ground wires were accessable. Big one on front of engine - back one by firewall - one big gouping connected to the back of the head we could not really get at, but we just put them on when installing the engine.

Checked terminals at starter R & S + big positive cable.

Got us stumped why the voltage reg wont kick in when on the vehicle. On the bench - no problem!

Where to look now?

Thanks in advance! Gil

Reply to
Gil
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If you check your output with a digital meter, what do you get? Your alternator may very well be wasted even though it was "bench tested".

Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

Reply to
Bigjfig

My anologe vom is fairly close +-.25V by eye reading. The alt output at big red terminl reads exaclty the same as the the dash

Gil

Reply to
Gil

Just buy a new alternator and battery... :-)

Reply to
Z24PODS says... "Click Here

Oh ok - never thought of that--- (senoir moment)

Ah!!!! Alternator & Battery are NEW as origanl post

Latest trail: jumped small termial on Alternator to try to get it to energize: get up to charging cap of 13.5v - no luck

Can the ECM turn the charging on this guy?

Reply to
Gil

A new battery and alternator won't solve a wiring problem :). Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

Reply to
Bigjfig

It won't?? Them basterds lied to me!!!!!!!! Just like the time I bought a brake power boster. The parts guy really thought if you put this thing on, you'll get more power out of your engine! LOL....... Now come on! Somebody has to have had a simular electrical problem out there? or just intreprt how the charging system actually works - get it? ok? ie: can read the GM manual's curcutry schematic, which we have. get it? ok?

Before this post goes south, Thanks Gil

Reply to
Gil

If ya can read the diagram and have the GM shop manual, I believe they have a troubleshooting chart in the manual. What did that have to say? :)

Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

Reply to
Bigjfig

Q: Does the ECM control any charging functions??? I'm gonna try a bone yard one next, if someone can tell me Y/N the ECM does have a charging system control/function.

Gil

Reply to
Gil

HEY OUT THERE!!!!!!!!!!!

A LITTLE HELP HERE PLEASE.

I'M STUMPED!

thx gil

Reply to
Gil

Gil:

You mentioned you have the GM shop manual for this vehicle. What does the troubleshooting chart in the book say? That's the first place to go and follow along.

It will lead you to the problem. Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

Reply to
Bigjfig

Ok I give. PLEASE Can anyone tell me if the ECM (brain box computer) has any bearing on the charging output???? Thanks Gil

Reply to
Gil

no it don't even gm isn't that stupid. the big term should have battery voltage at all times.the field term should go hot when the key is on. charlie 69' firebird 400 H.O.

Reply to
CButtacavo

I'm a Ford man, so this GM stuff has got me stumped. I'd really like to get this thing on the road & not take it to a shop so I can pay them to guess like me. Any other idea's on what to try next? Please e-mail me also, Its hard to check all the groups. Thanks

Gil

Reply to
Gil

I hate stuff like this because its all really a guess unless you have the right trouble shooting manuals from the factory. Here are a few things off the top of my head.... First off, although it sounds weird it could be possible for an alt to check out fine on the bench but when it actually is in the car it wont charge. Who bench checked it and how did they do the bench check? Did they open it up and check everything inside with an ohm meter? I don't know which cars had this problem (I cant remember but I think it was a GM) but here it is anyway. As far as i can remember certain GM engines had a bad or insufficient ground going from the alternator itself to the engine. Even though the alt is mounted to a metal bracket that is mounted to the engine it still couldnt get a good enough ground and the alt wouldnt charge. It seems impossible but i've seen it happen. More than likely this isn't your problem but at least its something to think about. You could always run a wire from the alt mounting bolt to a really clean engine ground to see if it helps. These cars do have internal regulators right?

Reply to
Mike

The plug that plugs into the alternator:

One terminal is for the light/gauge, and one terminal excites the field. When the battery is fully charged, turn on the key with the white plug removed from the alternator to see if you are receiving current to the terminals on the white plug.

When it was bench tested, they put twelve volts to the field terminal in the alternator. If you aren't receiving voltage to the white plug when you turn on the key, the field isn't getting the current to cause the magnetism, hence. No charge.

First look at the fuses, possibly there will be a charge, alt, batt, gauge fuse. it might be as simple as that. If not, you're in for some diagnostics.

I think the web site is

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and for like $25.00 you'll have access to every piece of diagnostic, and maintenance data for your car. Better than having a bunch of shop manuals, and what they don't have. Call the 800 number and they'll get it for you.

Refinish King

Reply to
Refinish King

As someone else mentioned, make sure the alternator is grounded. I have seen the brackets not ground a lot of times over the years on GM's. You can check that by taking a booster cable and running from the battery negative to the alternator case to see if it turns on.

My 86 Jeep runs the same GM alternator and it gets it's excite power from the coil power wire just before the ballast wire (on the 12 volt side).

I also have seen this same alternator have the wires switched on the small white plug on the alternator. Some versions have the A and B switched for some reason on different years of Jeeps anyway.

Maybe your harness is for the other version of the alternator and those two wires are in the wrong places?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Gil wrote:

Reply to
Mike Romain

Close King, it's

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** To email a reply, please remove everything up to and including the underscore in my email reply header.
Reply to
SgtSilicon

Thank you kindly for the correction:

I like to help, not give out misinformation!

Sincerely,

Refinish King

Reply to
Refinish King

Alldata is good, but they rip off the information from the factory shop manual.

I've paid as little as $15 for the factory shop manuals for my cars. A Haynes will cost you that and be totally wrong! Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

Reply to
Bigjfig

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