RPMs go up, Voltage goes down

[stubborn1]

I'm trying to diagnose an electrical problem on my 98. When I go to accelerate, the voltage gauge will start dropping once I am above 2500 rpms and the lights go dim. The higher the rpms, the lower the voltage. The battery light on the dash comes on at about 3500 rpms. When the tranny shifts or I reach cruising speed, everything is fine. My first thought is that the alternator may be bad, so I'm pulling it and taking it in tomorrow.

Is there anything else I might be overlooking?

 

[Xzibit A]

no its pretty much the alternator, it goes dwn cause the engine is using the voltage to run, did you check the tension on the belt too and the condition of the belt

 

[nascar_intimid]

could be the voltage regulator inside the alt. Just get a new one then you know what tou got without waisting your time repairing it only to have the brushes go on you next and then.... it never ends, just buy a reconditioned one...new if you have $$$

 

[lwn]

Ring on the stator has a short a higher RPM'S very common on Ford altenators. If it charges at an idle then the ring is expanding at higher rpm's causing a bad connection on the wire under it.

 

[WDP]

The stator rings are worn/egg shaped. When the revs rise the brushes or whats left of them bounce and make intermittant contact. Don't try to true the stator, it is only thin copper over a ceramic base and there isn't much left. Time for an overhauled one. If you go the junk yard route, get a fresh one, these die at about 90-100 K real regular.

WDP

 

[stubborn1]

Just an update -

I bought a cheap rebuilt alternator from Autozone and everything is back to normal. I guess 142k miles on the original is pretty decent. I went with the cheap rebuilt alternator with the lifetime warranty because it's an easy pull if something goes bad.