me1234

Hi guys,

I have a 1993 Bronco 5.0L 120,000 miles with a low voltage issue at idle. Yeah yeah I know another one of THOSE threads.

The symptoms: Low voltage, and occasional burning/hot plastic smell, this only occurs at idle, with the accessories on. The headlights dim and I get a slight miss as well so it's not just the gauge acting up. If I'm above idle I've got no issues at all.

I also get a wonderful groaning noise from the engine bay in reverse 60% of the time. This may be unrelated, but it will also stall in reverse maybe 5% of the time.

Let me say what I've done so far: New serpentine belt, idler pulley, and tensioner last year. I've attacked, relentlessly, the grounds, including the negative to the frame and block. It has new battery cables, and a new fan clutch(it needed it). I've had the alternator checked at Advance and Autozone multiple times and even had a shop check it and it comes out good.

Now, if it weren't for the occasional burning smell I'd probably just say screw it and deal with dim headlights at red-lights but this is my DD and I don't want to have a flaming ball of a truck or an issue on the highway.

The original belt was REALLLLLLLY old. Like massive visible cracks I can't believe it didn't snap or split in two old. I also may have some wear marks on the new belt but can't tell(pics coming soon).

My thoughts are leaning towards a belt slipping, stemming from pulley glazing from the old belt. However, what's weird is most sources I see say a slipping belt will squeal. I get no squealing, just groaning that sometimes accompanies the low voltage and that burning smell if I let the voltage stay low for too long.

Any thoughts?

me1234

Random poor photos of the belt.

nocturnalsuicide

If you are worried about a fire hazard than upgrading to a third generation alternator is something you want to do. The 2g alternators in these fords were pathetically weak, and the connecting clip for the positive alternator side were notorious for rotting out and catching fire. My 1993 4.9 would dim lights as well at stop lights. This was with all stock electronics, no extra lights or other equipment.

It is really simple to install a 3g upgrade. You just splice the two black wires from the old harness and run them to the 1/4 inch post on the alternator. The other wire in the harness gets run to the stator if i remember correctly. The other plug is re-used. If you run a high output model, you run an additional cable from the positive post directly to your ignition relay with a fuse in line.

me1234

Thanks! Yeah I think a new alternator is in my future. Good news is I'm pretty sure it is a slipping belt. Bad news is I made it worse.

I took a Scotch Brite pad to the pulley, and when I took the belt off I noticed mud was caked in the pulley grooves. I knocked all the mud out with a screwdriver and now my voltage goes down anytime my foots off the gas. I think the mud was actually increasing friction and helping me...

Anyways, for now I'm going to buy a pulley and a belt and swap those out while I save up for the alternator. I just moved into a new apartment so I should probably get a couch before spending a few hundred on an alternator lol.

Steve83

That photo shows a 3G alternator already. And if it has tested good several times, there's no reason to replace it. Replacement parts are LESS-reliable than originals (even 25-year-old originals).

Cleaning the pulley grooves can't hurt, but changing it CAN. I recommend you leave it, but wash the engine:


(phone app link)

What brand & PN is the current belt? Is the tensioner pulley near the middle of its travel range? Click these & read the captions:


(phone app link)


(phone app link)


(phone app link)

me1234

Thanks for the response!

My belt P/N is a Carquest K060990 6PK2517. The tensioner and idler pulley are Motorcraft parts I got off RockAuto and i'd say the tensioner is about the midrange in its swing.

I'm still working on the links you gave me. I've got some homework to do lol