Chargeing system

[dodge]

I have a 91 3/4 ton 2wd with a cummins, this truck was made in 10 of 91 and has overdrive and cruise. It will not charge the battery, I have put on 2 new ulternaters and i still have the problem, there is no voltage comeing out of the ulternater yet it test good if i take it off and bring it to be tested. Any ideas?

[cmann250]

1. Welcome
2. The wiring in these trucks is sketchy from the factory. Starting with a known good battery will save you alot of headaches. I played the battery, alternator, voltage regualtor game this summer. If the battery is old and nasty, it won't accept a charge no matter how good the alternator is

[dodge]

I have already replaced battery, only about a month old.

[cmann250]

Are these alternators new, or just different ones? I have heard that to test them, they spin them at like 3000 rpm. You'd have to spend alot of time at wide open throttle to get those results on your truck

[dodge]

new from AutoZone

[ellis93]

If your truck has o/d then the computer turns the alternator on,no external voltage regulator. The computer does this when it sees the motor is running, crank sensor tells it this. The crank sensor could be bad,if it is then the a/c shouldn't work either.

[dodge]

ok, Thanks, I will try that and let you know.

[dodge]

I just started it and it was chargeing fine, i let it idle and when it warmed up it stoped chargeing, should i still replace the crank senser or could it be something else?

[ellis93]

Two things first
1 how are you measuring the voltage
2 are these alts "brand new REMAN" autozone units. If so,then you could actually end up with a few bad ones.

Its weird that it should charge then quit. Sort of sounds alternator related. Just because they test it means jack siht, above post is correct on their "testing" process. If you spin them up that fast you can make one with bad brushes and burnt armature charge.

IMHO
Putting on Autozone rebuilt electrical parts are just about as worthless as pushing rope up hill. My theory on it is that the alt or starter is taken in and the one part inside that's bad is replaced and the rest is ignored.

[BobS]

.. things first
1 how are you measuring the voltage

AND what are you voltage readings USING a real hand held voltmeter at the battery terminals?
What voltage reading is at the battery terminals BEFORE you start it?
What voltage reading is at the battery WHILE it is charging?
What voltage reading is at the battery when it quits charging?
What voltage reading is at the battery after it quits charging and you turn on the headlights and put the heater on high?

The charging system is designed to replace the power consumed from the battery and does not provide additional charging when there is no load placed on the electrical system.

ALSO, does your truck have a crank shaft position sensor? Is it gapped correctly and are the wires and connections intact?

[Mark Nixon]

A 1991 does NOT activate the charge circuit via a crank sensor, as there is no crank sensor, even on a 1991-1/2.
All 1991s are externally regulated.
10 of 1991 means your truck is a 1992 model year.

1. It has the regulator in the ECM behind the battery.
2. The crank sensor is what initiates charging in the ECM.

Off hand, from what you are describing, the simplest things are probably the problem:

1. Bad Crank Sensor.
2. Bad ECM.
3. A heat sensitive problem in the alternator (worn brushes, or open winding), that opens up when it's warm.

I've said it before and I'll say it again!
DON'T blame the wiring in the truck, as 95% of the issues I've found in the wiring on these trucks is trackable to OPERATOR ERROR somewhere along the way.

I have an '07 here that went up in smoke all because they didn't use a fuse or circuit breaker on the power-up side of the solenoid, so when the wire rubbed through it lit the insulation off.
It wasn't even related to the stock electrical.

Mark.