alternator – alternating between working and not.

[al]

I have a 00 durrango and long story short last winter the problem started. I was driving and the gage dropped to 0 volts/amps.. it only happened a few times but I found that if I tapped the alternator with the ratchet I kept in the car that it would hum and my lights would go bright and the gage would return to 14 volts. it only happened maybe 4 times threw the winter but was good all the rest of the winter, spring, summer and fall now that its cold again its nonstop. I drive this car long distances.. kind of sketchy. I took it off the car and had it tested. was good. I put it back on, turn the car on and it gives me 11 volts, with no hum. I tap it with the ratchet, it hums and I get 14. I get in the car, start driving and pretty fast it dies. goes to 0 volts. gage zeroed, and soon everything will die. I hop out, pop the hood, hit the alternator…hum, lights bright, 14 volts..i do not believe the alternator is bad.. just somethings not right.. belt tension maybe? I noticed the tension pulley kind of moves when engine running. any ideas guys? I would really really appreciate it. thanks in advance.

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[Mike]

If all the wires to the alternator are tight and look fine, then you should believe you have a faulty alternator. The procedure that you use to get it working again is referred to by professionals as a “tap test”. The fact that your component shows operational change when physically struck means it fails the tap test, and shows conclusively that it is a problem.

[al]

the reason I believe that it works is that when taken off and took to autobone for testing it worked for 14 when tapped it stayed true the whole time. why would it preform on the testing machine and not when on the vehicle? thank you for your reply

[Mike]

In theory, the only difference between the bench test vs. live in the car is the connections. There is another side to it though that is unique to Chrysler, which is that the voltage regulator is not part of the alternator as with virtually all other cars. The PCM uses one of the wires on the alternator connector to control voltage output. I don’t know if the bench tester is able to simulate that PCM-controlled voltage or how it might behave differently on the test bench.

Normal alternators are a package deal and all you have to do is have it spinning and provide 12v to the exciter terminal to switch it on, and it outputs whatever voltage the internal regulator is designed to (as best as it can).

[Gary]

I suspect a faulty alternator. If you have to tap it occasionally to make it work, it may be worn out.

EDIT: Fopeano makes a great point about the voltage regulator. I would look into that as well.

[Erin]

Something I noticed also –
You said in winter, when it is cold, is when the alternator acts up.
Now the bench test – the alternator is then in 70 degrees where it won’t act up, assuming the alternator is at fault.

[Kevin Trillo]

replace it, on bench and in car are totally different test, when on the bench it has no load on the alt. i.e lights, radio, and any other electrical systems that may be running on it, you can troubleshoot and try to put more tension on the belt. i had a problem with a 05 mazda where the vehicle was fine then i notice my wipers would get really really slow and my lights would dim but if i was going about 60 its would be fine a couple weeks later the alt shit the bed and i had to replace it. anyway i would replace it, sounds like it is starting to shit out

[Author]

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