'99--battery light flashes

[bowtieboy12]

Anyone know why the battery light would come on with higher RPM's? usually at about 3,000 rpm's the light starts flickering and the more the R's increase the faster the light flashes til it just stays on around 3,500 rpm's. Sometimes it waits til 3500rpm to start flickering, sometimes til 4000rpms, but usually starts right at 3000. I thought at first the regulator could be shooting too many volts out at high R's, but hooked up a meter and it actually went from a little over 14v to about 13.5v with increasing rpms.

Anyone with any ideas? battery? alternator?

I'm planning on buying a scanner just haven't actually done it yet, maybe today I will. And suggestions on best OBDII scanner?

[GTP Dad]

Check the belt. This sounds like the belt is slipping at higher RPM's. It is possible that either the belt is bad or the tensioner is not holding enough pressure at higher RPM> This would cause the light to flicker. Also check the alternator wire to make sure it is tight.

[bowtieboy12]

well the belt is new a few months ago so i wouldnt think that is it, i havent had a chance to check the wires yet but like i said the voltage is about right? anyone? anything?

[Selectron]

I'd go along with GTP Dad and say that the belt condition or the belt tension would be the most likely suspects. Also check that the belt and pulleys are free from grease or oil, because it does sound very like belt slippage at higher RPM.

The battery charging warning light illuminates when the net flow of current is from the battery to the alternator (battery discharging), and it extinguishes when the net current flow is from the alternator to the battery (battery charging). If the belt, the belt tension, and belt/pulley cleanliness all check out ok then the fault is likely to be in one or more of four items:

Battery
Wiring and connections
Alternator
Regulator

Speaking as an electronics engineer, I can't think of a battery fault which would cause the symptom you describe. Even if the battery had started to fail and go high-impedance (which would cause it to not accept a reasonable charging current) then that would already be evident because you would have trouble operating the starter motor long before the poor charging symptom showed up. Likewise with a weak or shorted cell - it would show up as an engine starting problem first. Therefore I doubt that the battery is at fault, assuming of course that the car has been starting normally.

I'd start fault-finding by making a thorough visual inspection of the wiring and connections between the alternator and the battery, looking for any signs of corrosion, which would cause a high-resistance. It's worth noting that a poor (high-resistance) wire or connection between alternator and battery would have no immediate effect on starter motor operation, since the starter motor runs directly from the battery.

After the visual inspection, I'd then measure the voltage at the alternator output (B+) terminal, as described on the Alternator page of the Autozone Escort repair guide. The relevant pages are:

General information
Alternator precautions
Alternator
Regulator

Keep in mind that your battery is no longer charging normally via the alternator, so you may need to top it up with a charger occasionally until you get this problem resolved, otherwise you may find yourself stranded somewhere with a flat battery. Good luck.

[bowtieboy12]

When you put it that way I guess it makes a lot of sense, I'll check today when I get a chance, thanks