Alternator will not charge

94PROTEGE

MEMBER
1994 MAZDA PROTEGE
1.8L
4 CYL
FWD
AUTOMATIC
100,000 MILES

I have purchased and installed four batteries and five alternators. My battery light only comes on when I give it gas. Even when I have a full charge on battery. I put multi meter on it and it says alternator is okay. I have checked all my grounds all connections and all fuses. The belts squeal from complete stop until you are in second gear. I cannot figure it out and I am out of ideas or things to check. The only thing I did not change yet is the PCM. I was told that it might regulate voltage. Please Help! I am getting desperate.
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1 Reply

CARADIODOC

MECHANIC
33,742 POSTS

I need numbers to analyze. Specifically, start with the battery voltage while the engine is running. That must be between 13.75 and 14.75 volts. If that is okay, it just means it is okay to perform the rest of the tests, but that requires a professional load tester. Find me the values for "full-load output current", and "ripple voltage". Most testers just show ripple voltage on a bar graph between "low" and "high". That is good enough. Testers that make printouts show ripple voltage as a value. That is okay too.

It is not likely you have so many bad generators. I could see one, or maybe two, but if these are rebuilt units, at least one should have been working. You mentioned two clues that point to a slipping drive belt. That is the squeal and the warning light only turns on at higher engine speeds. Your mechanic needs to raise engine speed to 2000 rpm for the full-load output current test. He should notice the slipping belt, and that will show up as reduced generator output current. Inspect the belt to see if it is dry-rotted. That will reduce its grip on the pulleys. Next, tug on it to move the spring-loaded tension-er pulley. That should tighten the belt up when you let go of it.

Another elusive cause of your symptom is a broken harmonic balancer. Many have a cast outer ring glued to the hub, and the drive pulley is cast as part of that outer ring. The bond can break and let that ring slip. To identify that, place a chalk line across the front of the assembly so it crosses the ring and the hub. After a while, check if the line is still one line or if the two parts of it shifted from each other. That will tell you if the ring is slipping.