Ignition System Question

CONCH_E_JOE

MEMBER
1996 CHEVROLET TRUCK
V8
4WD
AUTOMATIC

I have a friend with a mid to late nineties chevy 1500 pick up. 350 v8. He has a loose battery post (positive) and on occasion has to twist it a little to snug it up so the truck starts. I noticed though, that while the truck is running, if you disconect the battery it will shut off. His alternator seems to be working just fine. It supplies 13-14 volts with the truck running and lights and stereo on etc, and his battery always has a charge. I have never had a car or truck that would cut off with a good alternator if you removed the battery terminals and was just curious why his truck will? Truck runs like new so I am asking just for knowledge.

1 Reply

CARADIODOC

MECHANIC
33,871 POSTS

AGGGHHHH! Don't remove the cable with the engine running! That is a trick that was done many years ago by people who didn't understand how these simple systems work. If you speed up the engine, without the battery in the circuit to smooth out the AC ripple coming from the generator, the system can easily reach 30 volts or more. That alone will destroy every computer on the vehicle and any light bulbs that are turned on.

What's worse, starting with the 1987 models, GM's generator is the worst pile in the world and they have no plans on improving it. Due to its design, it produces huge voltage spikes that can cause all kinds of problems with signals radiating into other wires for computer sensors. These generators even have special zener diodes to dampen the voltage spikes. When the battery is not in the circuit to absorb them, the voltage regulator sees them as system voltage too high so it tells the generator to cut back, ... So much in fact that it just about quits working completely.

It is also very common to go through four to six generators in the life of a GM vehicle. What many professionals are finding out is to reduce the repeat failures, you must replace the perfectly good battery at the same time. It will work fine in older cars, but as they age, their "internal resistance" goes up and they lose their ability to absorb those voltage spikes.

Caradiodoc