What do I need to fix? Here are the details.

JCB2525

MEMBER
1999 CHEVROLET MONTE CARLO
155,000 MILES

What do I need to fix? Here are the details: 99 monte carlo, 3.1L V6, engine light NOT on. Vehicle starts and idles fine. While driving, when coming to a stop my interior lights dim like it is losing power, they stay dim until I accelerate again. After accelerating it takes the vehicle about 5 seconds and then I hear a squealing noise, which I assume is my belt or a pully, and the vehicle regains the power. My interior lights come back to full power, my car seems to be accelerating better, and all is well. Until I hit the next stop sign. This has been happening since two days ago, and more recently (as of this morning on my way to work) my car even loses power, (interior lights dim) while driving 60mph. Then after 5-10 seconds, I hear the squealing noise again and it regains power. I have a hunch it could be my alternater finally going out but I want to be sure its not something more serious. Please help! Thank You!

Thursday, February 21st, 2013 AT 2:10 PM

1 Reply

CARADIODOC

MECHANIC
34,331 POSTS

There's two things to look for. The most common is a defective diode inside the generator. That will reduce its output capacity to exactly one third of its rated value which isn't enough to run the entire electrical system, especially at low engine speeds. A professional load-test will identify that by the lower than expected output current and "ripple" will be very high. If the generator is defective, replace the battery at the same time unless it is less than about two years old. The damage to the diodes and / or voltage regulator is caused by huge voltage spikes these generators develop, (which can also contribute to elusive engine running problems). As the battery ages, it loses its ability to dampen and absorb those spikes.

Given the additional dandy symptom you mentioned about a squeal, there may be nothing more wrong than a loose belt. If your generator has an external fan right behind the pulley, push on that with your thumb. (Please do that with the engine not running)! If you can spin the pulley at all under the belt, it's too loose. Next, tug anywhere on the belt and watch if a spring-loaded tensioner pulley moves and springs back freely. If one is used and it's not springing back freely and maintaining tension, it must be replaced.

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Thursday, February 21st, 2013 AT 4:07 PM