I have been having trouble starting my car lately. What I get is no cranking but a single loud thump/click from the starter. If I tried long enough it would finally crank. Checked the battery and the voltage was fine at 12.5 volts but I went and had it tested at work(walmart automotive). Found out the battery was only putting out 400 amps so I got it replaced for free(walmart max battery has 3-yr free replacement). Car then started fine for about a week but now its back to the same old crap. The other night I had to get jumped to get home... fired right up when it was jumped too so again I think this brand new battery is bad. So the next morning I pulled it in the shop and tested the new battery to find out it was fine but said it needed charged even though it was putting out 12.5 volts. Of course since it was showing "good battery" I couldnt try another one.

So my question is.... Should I keep pursuing this bad battery theory or should I look elsewhere like at the starter?

 

You could have bad connections, a bad alternator or a bad starter. The first thing to do is eliminate any wiring from the picture. Clean all connections at the battery, the positive cluster, the ground cluster the ground strap and the ground above the starter. Now check the voltage across the battery with the engine running to see that it is near 14 volts. If all that is ok, it may be the starter is bad and is now drawing too much current.

 

I already checked my alternator and its working great.. showing a good 14 volts.

 

The next thing to do is check to see how much current is being drawn from the battery with everything off. It could be you have something draining the battery down when everything should be shut off. I know that big thumping amps and SDM's can go fluky(did I spell that right) and draw current when they shouldn't. Easy check takes only 3 minutes.

By the way, have you checked the alternator output for any AC leakage from defective diodes? I wouldn't expect it since it usually causes the PCM to weird stuff but stranger things have happened. Another 2 minute check that is easy to do. And you don't even have to remove any wires.

Last thing, has it ever cranked slowly before?

 

Damn thing wont start again.. Im gonna have the battery tested once again. I dont have any aftermarket audio equipment and nothing has changed besides a head and LT header install since this began.