My alternator gauge shows around 14v at idle and running down the road most of the time. However, when I have lights and/or wipers going, it drops just under 12v at idle and at red lights. My turn signals also slow down somewhat when idling. As soon as I hit the gas, the blinkers speed up and the lights brighten. Any clues? Thanks

 

I would guess it's the Voltage Regulator (VR) in the PCM/ECU (computer). I've got the same problem (1993 B250 5.2) and I'm waiting to get a new PCM. When I bought the van the previous owner had got an external VR fitted which kind of stopped the volatage going too high but it's a bit of a hack. I got flamed here for even thinking this was a good idea (joke)..

I'm a novice but the experts on here will help diagnose the issue I'm sure.

good luck

Wilbo

 

I was afraid of that. I saw something like that elsewhere. I wonder who came up with that bright idea. Kind of like the TV/DVD combo. When the TV goes bad, the whole thing is bad. I guess I'll just keep running it until it quits. Right now it's just bugging me!

 

It's not the fault of the VR, the alternator just cannot keep up with the electrical demand at idle speeds. It might claim to be a 90 or 130 amp alternator, but it can only put out that much current at 2500rpm or above.

Upgrading the alternator will not put out any more amps at idle speed unless the alternator is physically larger.

You can put a smaller pulley on the alternator, but if you regularly redline your engine you could overrev the alternator. A smaller pulley could also slip easier, and causes faster belt wear.

If the battery is getting weak the lights can dim at idle as well.

One thing I have found on mine, is that the charge wires leading to ground and battery (+) are too small a gauge(6 or 8). The fusible link has also been replaced with one that it too small(14awg). It heats up significantly whenever my batteries or other electrical systems demand more that 25 amps. The hotter it gets, the more resistance, the less amperage flows. It's bad for the alternator, it's bad for charging the batteries.

My blower motor draws about 18 amps on high
My low beams draw about 14 amps
My hi beams draw about 20.
Un amplified dash Stereo 0.8 to ~5.2 depending on volume/bass
Fuel pump draws 4+ amps and just turning the key to run not start( after the fuel pump stops) draws about 3.5 amps. So I'm guessing the engine needs about 7.5 amps from the alternator or battery just to run.

So once the engine is warm and no longer idleing at a higher rpm, and once the alternator is hot, and less efficient, and the charge wires are warm/ hot and highly resistant, the alternator simply cannot keep up with the demand.

Unless you do short trips with prolonged idling, don't worry about it. Put your battery on a wall charger once in a while. Or put larger wires on it, and a smaller pulley.

http://www.alternatorparts.com/FAQ.htm

http://www.aa1car.com/library/charging_checks.htm

 

landyacht318, you may be right. The guy I bought the van from 3 weeks ago said the original alternator was seized when he got it and he put another one on. I suspect that he got it from a u-pull-it yard because it isn't anywhere near new looking. I think I'll run by Autozone and let them test it.

 

Before ripping out the alternator to have it tested, clean all the connectors leading from the alternator to the battery. There are several in line connectors, and each one causes a voltage drop, and restricts alternator current. You can try just adding another fused wire between the alternator(+) and battery (+)

I have 3 batteries in my van, with a battery monitor which shows alternator amperage, and the stock wiring just is not designed to handle charging 3 batteries.

I will soon be ripping out the stock wiring and adding a shorter length of some thick cable(2 awg).

Read through those links thoroughly, there is a lot of good info there.