Starting Issues
 

I bought a 1998 Z71 4X4 Chevy pick-m-up - gots high miles but sound enough - at least it was. The battery was many years old - it was struggling starting so I tried charging the battery. Wouldn't really take a charge, would not turn but it would back fire every so often so I bought a new battery. Started up so I thought all was good. Few days later same thing. What do you think it is?

Something draining the battery down?

I thought that as well. It has a aftermarket sound system. I turned it off - actually I should just take it out and sell it / give it away. Maybe I'll put a meter on the fuses to see whats drawing juice?

I would start by putting a voltmeter on the battery before starting. Check reading. Then I would start the car and put the voltmeter on with the engine running. If output is greater than before engine started then alternator/generator is doing its job.If no change then alternator is not doing its job. Otherwise there could be a stealth drain on the battery.

The backfiring could be another issue altogether.
Guy

Alternator can be failing.

Start er up and turn on everything that uses juice.

Check the headlights to see if they are dim or flickering.

Take off the negative battery cable and install a multimeter in-line on AMP setting using alligator clip jumpers.
-That's the total parasitic draw. Key Off, Engine Off.
-A 12V test light probe will work also for basic test purposes.
-If there is any current flowing, the connector will spark when tapped on the battery.

If juice is flowing, now find which branch:
1). Isolate the alternator by disconnecting it from the red positive cable. The battery is disconnected when doing this of course.
2). Isolate other branches such as radio, alarm, other by pulling respective fuses.
3). When something is disconnected and amp flow drops to zero, or near, you've found the problem.

If it is equipped with a trailer brake controller I would suspect it. It's usually attached as an add-on wire to the battery + terminal. I've had a couple that drew the truck battery down over a 3 day period.

Disconnect the ground overnight and see if it starts fine. If it does you have too much draw when the ignition is off.

Might just be a bulb somewhere, like the glove box.

can you do this by removing branch fuses from the fuse box?

I've heard of alum foil, pennies, and bullets being used as fuses. But never branches.

Paul, is that you? Welcome back.

Got smart, sorry. ;)

(please correct if this is wrong!!! It's been a while since school.)
I think wiring typically goes from battery to ignition switch to fuse box to device to chassis/ground and back to battery/neg.
A circular chain.
Fuses are the weak link, designed to burn up before the wires.

Heavier loads will go through relays activated remotely by the ignition switch.
(They don't want too much juice right next to the hands in case it shorts out and there is only so much room through the steering column.)

Ignition modules are on the ground side for protection.
There is a lot of voltage there, seeking a path back to battery ground.
(Shorts will hopefully find another path back first before frying the electronics.)

hey Paul!!!

There goes the neighborhood :D

Yes, pull the fuse, use the ammeter to make the circuit.

But you should start at the battery to be sure you even have a problem.

this^^ my first move is always to pull out my voltmeter. you are totally guessing without knowing if the battery is healthy, or being charged.

Brand new battery. Hope its healthy and it isn't toast now...

Mike, there ya go again trying to start things......

Went through all the typical electrical diag - nothing anomalous presented itself. Tried jumping from another battery - nada. Looked at the PVC valve, took it off the valve cover head. Engines turned over. I wiped it off and put my finger over it - felt the vacuum so I put it back on. Shut the truck off and waited 15 minutes. Started up. Now it seems fine.

interesting