How do you check if the alternator is bad?

Use a voltmeter while the car is on, see if the voltage is around 14V. If not, have the battery checked. If it's okay, if a V6, make sure the red battery light on the aux gauges comes on. If light works, check wiring to alternator (two wire connector and large wire). Using multimeter, check continuity between large wire post and battery positive cable. If there is continuity, suspect alternator. Take out and get it tested. If after removing the belt, you cannot spin the alternator pulley by hand, or if you can and you hear grinding or similar, bad bearings, which may have burned out internal components.

well, maybe you can be more help. I have a 1987 Pontiac Fiero V6 2.8 liter. My voltmeter is now in the red zone. Many said its the fusible links, some said alternator and others said it can be the voltage regulator. Is their anyway I can narrow it down to one of those?

Thanks

Quick way to see if it is charging enough to run the car. Disconnect the positive battery cable with the car running. If it dies, alternator is weak or dead. This is not a 100% perfect, but just a way to check to see if the battery is doing all the work.

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11 Camaro SS/RS
86 Fiero GT
03 Silverado 3500 Duramax! (Stacked, Tuned, Mean as Hell)
07 Suburban LT2
09 Avalanche LT3

quote Originally posted by pontiackid86: i'm sure i could fly a plane no problem.

well, maybe you can be more help. I have a 1987 Pontiac Fiero V6 2.8 liter. My voltmeter is now in the red zone. Many said its the fusible links, some said alternator and others said it can be the voltage regulator. Is their anyway I can narrow it down to one of those?

Thanks

I don't think it will explode. You should be fine. You will know right away if it is not charging when you pull the cable.

Remove alternator and take it to local auto shop, they can test it off the car for free, that would tell you if its a fuse or wiring.

quote Originally posted by Carver1: Quick way to see if it is charging enough to run the car. Disconnect the positive battery cable with the car running. If it dies, alternator is weak or dead. This is not a 100% perfect, but just a way to check to see if the battery is doing all the work.

I have heard not to disconnect the battery cable with the engine running as sometimes this can cause problems with electronics... ie.. the ecm.

I would suggest to just drive the car to Autozone or Advance Auto Parts and have them test it in the car. It is free and easy.

DO NOT DISCONNECT THE BATTERY WHEN THE CAR IS RUNNING!!! You defiantly run the risk of damaging the ECM, Radio, alternator and any other sensitive electrical components in the car. You also run the risk of causing a spark near something that is producing hydrogen (especially if it’s over charging) and hydrogen will go “BOOM” in a big way (I’ve seen it, it’s not pretty). Sounds like the alternator is possibly over charging. If so, you don’t want to run the car more than necessary (not at all if you can get away with it). Best thing is to pull the alternator and have it check. When they check it make sure that it’s not going over 14.5VDC or less that 13.5VDC (I don’t like less that 14). If you don’t want to pull it first, start the car and see what the voltage is at the battery with the same specifications. Keep in mind that an over charging alternator can do damage (again) to electronic components and the battery.

quote Originally posted by Carver1: Quick way to see if it is charging enough to run the car. Disconnect the positive battery cable with the car running. If it dies, alternator is weak or dead. This is not a 100% perfect, but just a way to check to see if the battery is doing all the work.

You'll be s o r r r r r r r r r r r r r r r r r r r r r r r r r y.

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

we know its the alternator. does anyone know if the voltage regulator is in the alternator or on the outside?

Voltage regulators haven’t been separate units for 30 years. They are internal and you can replace them but it’s usually much better to have the whole thing rebuilt (or buy one already rebuilt). I’m a fan of finding a local rebuild shop (check them out to make sure they are legit). For a rebuild shop to survive they need to do quality work. When you get a rebuilt unit from an auto parts store you don’t really know what you’re getting. I’ve seen more than one alternator (or starter for that matter) where the rebuild was nothing more than replacing the brushes and cleaning it up.

we know its the alternator. does anyone know if the voltage regulator is in the alternator or on the outside?

quote Originally posted by hckyplyr55: thanks, we have soneone checking it out tomorrow

Do yourself a BIG favor and upgrade to the 88 style CS130 alternator. All you have to do is buy a CS130 adapter wire plug. Same fit and belt. This model is more efficient and reliable and doesnt suffer from heat soak death.

NAPA used to carry rebuild kits for our alternators. It included a new regulator, brushes, bushings and diodes. Cost about $15 five years ago. Took about 30 min to assemble once the alternator was off the car.
By the way. If you have an 2.8 with auto trans the alternator comes out through the right wheel well after you move the skirting and tie rod out of the way. Stick shift will come out the bottom.

@2farnorth- its five speed.

The car is now running fine.

If you go to a pick & pull what vehicles can you get a CS130 alternator from.

Okay, the alternator was changed. The car ran at 13 volts for 25 years. Now that the new alrernatir is in, its running at 14.5 volts. I checked it with a voktmeter. Is it okay and safe to drive at 14.5 volts?

That’s right where it should be.