Intermittent Charging Problem.

ruddy · November 3, 2007

I've got a frustrating charging problem. My truck will run fine for several days with a charging rate up around 13.8 to 15 volts. Then when I start it up one morning, it won't be charging at all, and the voltmeter shows 12 volts. If I drive for three or four miles and shut off the engine, it's charging again at the usual rate after restarting. It will then charge for the rest of the day. On one occasion, it started charging after I had driven about seven or eight miles. It will do this quite consistently until I disconnect the battery and reconnect it. Disconnecting the battery seems to cure it for a few days.

I replaced the alternator last March, and the battery is three years old. I recently cleaned the battery terminals and cable connectors.

Any ideas?

Zembonez · November 3, 2007

I've got a frustrating charging problem. My truck will run fine for several days with a charging rate up around 13.8 to 15 volts. Then when I start it up one morning, it won't be charging at all, and the voltmeter shows 12 volts. If I drive for three or four miles and shut off the engine, it's charging again at the usual rate after restarting. It will then charge for the rest of the day. On one occasion, it started charging after I had driven about seven or eight miles. It will do this quite consistently until I disconnect the battery and reconnect it. Disconnecting the battery seems to cure it for a few days.

I replaced the alternator last March, and the battery is three years old. I recently cleaned the battery terminals and cable connectors.

Any ideas?

No dead battery issues?

I'd make sure all of the connections between the alternator and harness were clean and tight along with the battery cables. GM cables have a tendency to corrode internally near the ends. Especially if they are original to your 96 truck. I chased a starting/charging issue on our shop truck for a week once only to find out the cable that looked great on the outside was corroded up on the inside and losing connection. Another thing...Pay really good attention to your ground connections making especially sure that the engine is well grounded to the chassis.

Could possibly even be a gage issue or the regulator going out in the alternator but I'd check the wiring first if I were you.

ruddy · November 18, 2007

I replaced the cables, and it still does it. In fact, it will do it more than once during the day. Napa doesn't carry the six foot cable that runs from the positive terminal over to the left rear of the engine compartment. I figure I should probably change it too, since it's as old as the other two battery cables.

Does anyone know where I could get one other than a Chevy/GMC stealer?

Thanks.

ujtruck · November 18, 2007

its look like you have defective voltage regulator, get your alternator tested, also battery.

Here is some more info:

If the alternator or regulator fails, the battery will run down and the vehicle may not crank or start. Low voltage or amperage output from the charging system will usually cause the alternator warning light to glow, the dash voltmeter to read low, the dash ammeter to show discharge or the Check Engine light to come on. The headlights will also be dim when the engine is idling. Low alternator output can be caused by a slipping drive belt (it takes up to five horsepower to turn some alternators), one or more defective diodes in the alternator's rectifier assembly or a defective voltage regulator. Loss of alternator output can be caused by a broken drive belt, loose, broken or corroded wiring connections, electrical failures within the alternator or regulator, or a bad external regulator ground or voltage connection.

In some instances, the alternator can produce too much voltage and overcharge the battery. Symptoms here would include low battery electrolyte, damaged battery plates from overheating and/or burned out bulbs. The cause is usually a defective voltage regulator or poor regulator ground connection.

Many alternators are replaced unnecessarily or are returned because of misdiagnosed charging problems. If possible, have your old alternator bench tested to see if it works. If it does, the problem is not the alternator. It could be a bad regulator or wiring connection. Also, have the replacement alternator bench tested before you leave the parts store to confirm it is delivering the proper voltage and current.

Make sure the replacement alternator's amp capacity matches the vehicle's requirements. Don't buy a 45-amp alternator for an application that requires a 90-amp alternator. Overloading an alternator will cause it to fail prematurely. What you may need is a High Output Alternator