everyone knows the voltage of a battery is 12 and when the truck is running it goes up to 13-15. with that being said when i turn my truck on the voltage drops to 11ish and it either fluctuates around 11 volts or sometime (actually right now) it starts to decrease to 9 volts then stalls. i got a new red top last month and a new alternator 30 minutes ago. the bearings were bad in the other one but was working fine. any idea what it could be guys? thx for ur help in advance.....

 

What was the voltage like before you replaced the alternator? And where did you get the new one from? Could be a junk alternator.

 

same 11ish. kragen

 

but it never let the truck die? How are your battery cables?

 

The new alt didn't change a thing! The cables r good. And I chked the fuse links and there good. Is there a fuse for the alt?

 

im having the same issue pretty much, when i stop to an idle.. my voltage drops alot.... and im pretty sure my altinator and battery are good... but its worse when i turn my cabin fan on (ac or no ac)

 

I'd make sure all your wires are good. Also did you change out the pulley on the alternator?

 

The pulley was new with the alt. When I disconnect the battery while the truck is running itstalls. Shouldn't it still run without the bat connected? I was thinking of this right now at work. I'm gonna chk to see if the alt is grounded.

 

Sometimes the pulley(s) on the new alternator are not the correct one(s).

 

Absolutely not. An engine cannot run without a battery, unless its like a lawnmower, dirtbike, or other things like that. Newer vehicles from like the 70's? on up are computer controlled and have to have power to read sensors, open injectors, etc. And the alternator grounds at the mount. It doesn't have a ground cable to it.

 

You want to check all cables from the alternator to the battery. And check your battery out with a load test. I had a similar situation 2 years ago where I could charge the battery up and then start the engine and volts would be about 13.5+ while running. But after I shut it down the battery voltage rapidly dropped. I had MotroCraft battery less than a year old and I didn't think that would be the problem - but I took it out and went to where I had purchased it and they did a load test on it - and sure enough, it would not hold a charge!

 

Grounds, wiring, belt, or maybe have the battery checked under load, could be a bad cell.