2008 voltage drop

[hernan]

I have 2008 chevy 1500 4.3 and as soon as i start my truck the voltage drops to less than 10v iv'e checked the battery and the alternator and they are both good,when this happens evry time i resets my computer can anyone help

[Jsdirt]

Starter could be drawing too many amps - they'll do that when the bushings wear out on the armature, or if it's partially shorted.

 

Does the starter sound normal speed as it cranks over, or does it sound slow? If the battery is indeed good, and it's cranking slow, either the starter is junk, or you've got a bad connection in the cables at the battery or at the starter.

 

Another thing to note, a battery can look good on a multimeter (12.6 - 12.8v), but not have the amp capacity to do much more than barely start an engine. This is where load testing comes in handy.

[txab]

I'd check battery cable condition and connectors

[Doug_Scott]

I have 2008 chevy 1500 4.3 and as soon as i start my truck the voltage drops to less than 10v iv'e checked the battery and the alternator and they are both good,when this happens evry time i resets my computer can anyone help

 

You don't say how you tested the battery and alternator. What you are describing does not sound like it could even be the alternator. As Jsdirt has offered, it will be a bad battery, or starter, or cable/connection. Not unusual for a battery with either a dead cell or becoming sulfated to not be able to supply the amperage needed to crank engine over without having the voltage drop below 10 volts.

 

Is the battery the original battery? If so, 8 years is about double the average life of a auto battery. When you say "voltage drops to less than 10v" are you talking about while the engine is cranking, or that is what it reads after engine starts? Are you using a voltmeter attached directly to the battery or the in dash gauge? Do you hear the engine crank very slow for the first turn or so, then speed up and engine starts? Don't be surprised if you end up needing both battery and starter. An old battery does not handle high amperage draws on a regular basis.

 

Near as I can recall, starter draw on an 8 cylinder engine should be about 150-200 amps, with anything over about 250 amps being excessive. This was back in the old non-electronic AVR testers. We would connect an AVR to the battery, and have someone start the engine while I was watching the voltmeter on the AVR. I would then have the car shut off, and then I would turn the AMP test knob in until the voltage dropped to what it was while cranking. The AMP gauge would show me the amperage being drawn by the AVR. The AVR test knob was basically a bunch of carbon pucks that were a variable resistance controlled by how hard you compressed them together. If battery voltage was below 9volts and the amperage was within allowable specs, it meant a bad battery. BTW, if you are old enough to remember ballast resistors on Dodges, the reason they were used was because while engine was cranking the ignition system could not get 13volts, so, the ignition system was actually running on 9-10 volts at all times. The resistor was bypassed during cranking. Other manufacturers used other means to accomplish this, some using a special wire in the harness, some using built in resistance in the coil. I know, off topic, just something about this that made me recall this trivial trivia.

[Jsdirt]

I built a shunt for my multimeter - it was a precise length of 8 or 10awg wire, with meter leads soldered to each end of it, positive and negative, along with small battery clamps. Plug then into the millivolt ports and set the meter to millivolts, clamp that wire in series with the starter negative, and you have a fairly accurate reading of amperage without turning the $200 meter into a fuse.

 

I had got the plans from one of my instructors at MMI Phoenix in the late 90's. I'm sure that info is readily available on the net somewhere.

 

 

I get between 8 & 10 years out of batteries, and I constantly maintain them with a 3 stage desulphating charger whenever they sit any length of time. My Silverado OEM battery was getting very weak at year 8. Required more frequent charges to keep it working. Capacity was way down.

[Doug_Scott]

I have seen those plans around before. When I was working, the shops all had the commercial AVR meters/testers on a cart. I have a Herbrand (that is how old I am) MultiMeter/AVR with a shunt type cable to test starter draw with. I think I used it once, it was faster to just use the shops tool since it did not require any cable disconnect.

[Jsdirt]

Yeah, inductive is the way to go - saves alot of time.