When in wot, with the headlights on, the headlights dim to almost nothing. The dash lights dim and the radio shuts off but does not lose its memory. When i let off the throttle everything goes back to normal and my alt is reading just over 13 volts.

I have just replaced the starter and and before i did it never had this problem. Any ideas?

 

bump

 

I just went this same/similar mystery voltage drop on my '86 corvette last month. My old alternator died on my, no surprise for a original alternator on a 25 year old car. I picked up a factory rebuilt Remy and after a couple of days the mystery voltage drop appeared.

Long story, short: the NEW REBUILT Remy was crap. There must be a break in the armature windings which at RPM separate and stop generating power.

http://forums.corvetteforum.com/c4-t...ator-woes.html

 

yeah my alternator is less than 3 months old..... guess i could take it back. It just never had this problem befor i replaced the starter. thanks for the link.

 

Make sure your belt is not slipping, I've seen it happen at high rpm on car where the belt loose or a bad tensioner.

 

ok i will check it out. thanks

 

ok so i tightened the belt. still have the problem. wonder why this is going on right after i changed the starter. Could it be the Starter?

 

Doubt it unless your starter has the guts of a alt and is belt driven..

Do you have a volt gauge? whats it do at wot? drop off? if so your alt is bad ooor you may have a loose connection at the batt.

 

in wot it hauls *** , never hesitates. but the very second i hit the gas the volt meter will drop, the dash and head lights dim, but not always. sometimes my radio just shuts off, but it does not lose its memory. The alt is brand new i even had it tested. Everything is clean. had no problems before. im lost on this one.

 

Anyone?

 

Get your alternator tested first before asking questions.

 

Put the headlights on and wiggle all the connectors on the big batt cables and grounds, see what happens.

 

yes i forgot to mention i had it tested it cam out fine. Got it tested at autozone.

 

Had a similar thing happen to my blazer a few years back. Year old alternator would charge fine at idle and cruising. But as soon as the RPMs went up it stopped charging. Let off the gas and it would start charging again.

 

Okay very easy to test, first there's a 12v power supply to the alt with ign on, you need to check this(edit read below) first, next you need to test at the back of the alt to duplicate the problem, this is where it's get creative, you need a multimeter, run a 10g wire from the back of the alt into the car and check the readings at the speed and rpm to point of problem (the wire is not fused so make sure you don't short it otherwise you will need a new alt and batt maybe) if voltage drops then do the same to the 12v ing on wire to see if its losing the 12v there, if its not then you need a new alt if the belt is not slipping, if its not dropping voltage at the 10g wire then you need to go the starter, disconnect the batt and check continuity top and bottom of the fusable links.

Also make sure you have at least 3 grounds, 1 from batt to eng, 1 from batt to body and 1 from end to body, check is first!

 

OK I had the exact same problem after I replaced my starter and the culprit was extremely unusual. I had just replaced the starter with a smaller LT1 unit and so I did not need to use the L-shaped support bracket that attaches at the rear of the starter.

Being lazy I just left the bracket dangling from the block by its attachment bolt. Well, on WOT the bracket would pivot at that bolt, swing backwards, contact the starter terminals and short everything all to hell until I let off the gas allowing the bracket to swing forward and everything would be back to normal.

Never figured it out until this one time the sparks from the bracket shorting at the starter were so violent the bracket got welded to the starter terminals and the battery positive terminal puked lead and broke off. The car went dark and rolled to a stop. I had to replace the battery, and the starter positive cable. Oh and I removed that pesky bracket.

Moral of the story? Check all the connections at the starter, make sure all those bolts are tight and that wires aren't moving around when you go WOT.

 

Checking the output "S" Terminal should have been the first thing (before even posting ) Do NOT disconnect the post just check voltage while running.

But when checking the field "F/I" terminal things can get a little weird. You can unplug the connector (with the engine running) and no harm will come to the alternator. The field terminal only needs voltage initiate the magnetic field. After the alternator starts charging it doesn't need the field voltage, BUT (depending on the regulator model) voltage is sensed at this terminal for the warning light so any drop off will trigger the lamp/gauge.

http://oljeep.com/gw/alt/edge_Altern...html#Section_4

I checked the field voltage and had power (un-plugged, engine running). When I used a jumper between the alternator and wire to sense voltage, it would drop at high throttle (because of the bad alternator). Checking the alternator at low/normal RPMs it was fine. On a test stand it was fine. At 4000+ RPMs -> CRAP.

 

OK so its been a while since Ive posted any updates but i got the problem at Wot to go away by replacing the alternator even tho the one i had was new.

BUT NOW!!!!.......... i drove it around a while with no problems at all until one day my guage to drop to 8v

here is whats been done

New alt to bat wire
new ground, ground to body and another ground
new alternator, after i turned in another one that passed a test but they exchanged it anyways (tested in another car to be sure it was working!!)
new alternator belt nice and snug on the pully
all connections appear to be good.

now i tested the back of the alt at the single post,engine running and got 8v. i thought it would be at least twelve.

what else could it be?
i figure it cant be the alternator is passed and brand new! although its only reading 8v. help!

 

o and where are the fuseable links located ?

 

i think i have narrowed this down to a computer problem

 

What computer?

Do you mean the ECM?

The regulator?

 

not sure yet all i know is that it can be a problem with the ecm. i think the regulator is inside the alternator and that is new.. I never had to go this deep into a charging problem before.

 

I can't see how the ECM could affect the voltage.

You have probably either a faulty alternator or regulator.

It could also be a poor earth or bad connector.

 

I think you've ventured out into Left Field; the ECM does not control the regulator or alternator on these cars .

Back to your problem: Have you checked your field voltage? Explain your testing procedures so far and maybe we can help. It sounds like you are buying discount parts store alternators (read: junk).

 

I had someone tell me that one of the three wires was could have been controlled by the ECM. turns out he was wrong.

So i realized searching forums is a fine art ,got to find the right terminology. So i have done some extensive research and have come up with this.

The wire that should have 12v with key on is linked to the C/H Fan Fuse so I am going to start today by checking it at the fuse box and checking the fan relay. I am a little worried because i know the fuse for the fan is good. will post back soon.

i will keep you all updated.

 

He could have been right if he was talking a later year GM (CS130D) or some other Make vehicle, not for a third gen. Check your voltage at the harness plug F/I ("field") terminal.


http://oljeep.com/gw/alt/edge_Altern...html#Section_4

 

So i checked the CH-fan fuse and had a solid 12+ voltage.
checked the wire.... was good. tried everything without fixing the problem.

Then i decided the only thing i did not do to charging system was change that CH-Fan fuse.

Then i fired it up i got a almost 14v with all accessories on. which is strange because looking at the fuse it looks flawless. I put it back in to see if it was the problem and the car failed at charging. Bad fuse was the whole problem. I think it was just caroded enogh to break the conection but the apread to be no serious corrosion

i have never had the car run this kind of voltage before. at the most it would run @max 12 volts a little under with every thing going. She has never run better and i now i know how dependent these cars are on the charging system.

Thanks everyone for your help on this. This website is the only reason that car is not in the junk yard.