[canadaboy25]

On startup, the belt on my 95 will squeak for a long time before it quiets down. Normally I would just replace the belt but there is a pile of belt powder on the face of the alternator. I wiped it off and ran the vehicle for less than 5 minutes. I shut it down and removed the serpentine belt. The alternator was covered in belt dust and the pulley was hot enough to burn my hand. The body of the alternator was quite hot as well. The battery is not dead.

The alternator coils looked pretty dark to me but when I was looking at the price of new alternators, the coils in the pictures look to be the same color.

The other thing that makes me suspect the alternator is the tach does not work. When the vehicle is running the tach will sit at 500 RPM regardless of actual engine RPM. Rarely the tach will function normally but not very often.

Thoughts?

 

[rangerover]

If the alternator is still charging, then perhaps you have just a bad idler pulley instead.

The tach gets it's reading from the alternator so double-check the connections on the bad of the unit.

 

[canadaboy25]

The belt runs to the AC compressor from one side of the alternator and to the power steering pump from the other. If the idler was bad wouldn't the belt dust show up somewhere else instead of on the alternator?

I have tried wiggling the connections on the back of the alternator but it has made no difference. I will try removing them and cleaning them to see if that helps.

 

[rangerover]

I was thinking along the lines that the squealing is belt-slip and the idler is what is going to tension the belt.

Another possible culprit is an internal component within the alternator that isn't transposing a signal beyond 500rpm. The voltage-regulator might still be okay which is why it's still charging but beyond that, something is failing.

Might not be bad to start looking for a replacement device just in case.

 

[canadaboy25]

Well it turns out the thing isn't charging. The times that the tach worked, I noticed a slight drop in RPM when it happened. This must've been the alternator starting to charge. Could the alternator be losing a signal that enables it which is causing the intermittent behavior?

 

[aussiebushman]

Rather than spend a lot of time trying to fix what sounds like a dud alternator, it only costs around $100 for a new aftermarket 100A alternator. That may sound like a lot of money but it could potentially save you much angst and fix the problem very easily. You can do it yourself without paying a technician. Just be sure to make a sketch of how the belt fits before removing it

 

[canadaboy25]

I don't know where you're shopping but the alternator cost me around $300. Anyways I put the new alternator on and now the system is charging, however the tach still does not work. I put an oscilloscope on the W terminal of the alternator and got a signal that did not vary with engine rpm. This is consistent with the tach displaying roughly 500 RPM all the time. While I was looking at it the alternator changed tone slightly and the tach jumped up to about 900 RPM and worked normally which was reflected on the oscilloscope. I turned the engine off then on again and the tach was back to being stuck at 500.

I tested to make sure the alternator had a good connection to ground and power and that the alternator is receiving constant battery voltage to the D terminal. To make absolutely certain the alternator was being commanded on, I ran a jumper from the D terminal to the positive of the battery. This made no difference. When I grounded the D terminal the battery light came on the dash as expected

The alternator is just a 2 wire internally regulated alternator with a tap for the tach signal. If it has good power, ground, and enable signal, it should work fine.

Looks like a dud alternator? It's an AC Delco but it says re manufactured so you never know.

Thoughts?