buugiewuugie

This morning my truck started displaying the battery light when I take the truck over 2000 rpms. It is in the same spot every time, right at 2k rpms. As soon as it drops below 2k the light goes out. There is no noticeable change in the truck when the light is on. I had the battery and alt checked at Advance and both were normal. I revved it to 4k and the guy said it dropped down to 12.5volts, but that was normal. Any ideas what the problem could be? The cables and terminals at the battery are secure and no corrosion. It has a 7 month old battery and alternator.

Also this is a 2003 Escape V6

Thanks in advance

Lord Humongous

It's the alternator.

Fabrik8

If it drops down to 12.5V, that means the alternator is not producing power. The 12.5V is the battery voltage; the alternator has to go above that voltage in order to charge the battery and provide power for the electrical loads. Sooooo I don't think the alternator is working properly. IIRC, the lamp lights when there is no alternator output, which would match the 12.5V system voltage. I'm assuming that 2k RPM is probably some threshold where the voltage regulator realizes something is wrong based on the output voltage or frequency at that RPM. I can't imagine that 2k engine RPM would be the minimum regulation RPM for the alternator, but maybe that's another symptom that something is wrong.

[strike]This doesn't necessarily mean that the alternator is bad, especially if it tests properly at wherever tested it. Whether you feel you can trust that alternator test is completely up to you. I'm not very trusting. Anyway, it's possible that the alternator is bad, but it's also possible that one of the connections between the alternator and the rest of the electrical system is bad/corroded/etc. That could mean a blown fuse or fusible link on one of the sensing or output circuits from the alternator.[/strike]

Because it's RPM-dependant, I'm going to say that it's probably something wrong with the voltage regulator in the alternator. If it was lit all the time, I would say it could be a connection problem. If something else in the electrical system was forcing the alternator into a low voltage state (by drawing a shitload of power for example), you'd most likely see symptoms somewhere else.

Fabrik8

Oh, and don't ever test the alternator without a load like the battery connected to it.

buugiewuugie

Great. The last alternator job took about 5 hours. Not looking forward to this. The alternator is in the worst place imaginable in this truck.

Do you have any tricks/tips to narrow it down to the alt?

Fabrik8

You can test the individual terminals on the alt and see what their behavior is, and test that you have proper connections and good fuses, etc.. You'll have to Google that one. Most alternators are fundamentally the same though (and often the connectors from brand to brand are the same too), so testing instructions for one vehicle will usually work for another as long as the alts are similar.

wright

Take it to auto zone or another parts store and they can test it for free.

SortaFlush

Don't replace it with an Advance or Autozone Alternator.

White Devil

Agreed on this. Look for a performance alt for your make of vehicle. I saw that Bosch makes one, dont know about its quality tho.

T Lowgun

voltage regulator