Won't start with good battery but will start with jump - why?

Hi all,

Getting ready to take my Locost out of hibernation now that the weather is getting nice. It will not start with a new battery but it will start if I use jumper cables from another car. The terminals are tight on the battery posts, so I suspect that it might be the starter, but it seems odd that it would start with jumper cables if this was the case.

Any suggestions? If it helps, the donor engine is a Toyota 3TC from a 1982 Corolla.

Thanks, Mark

I'm going to go with questioning "Good battery". You might have a bad cell. It will charge and have good no-load voltage but a load will pull it right to zero. Have it tested.

I will also question the "Good battery". Take the "Good battery" and try to start another car with it.

And don't trust the battery testers at the auto-parts store. Either the guys don't know how to use them, or those things don't work, or they try to sell you a new battery, or....

I've had "bad" batteries last thru 3 more Canadian winters and "good" batteries refuse to start a car no matter how long the charge.

+1 to GPS. Start with the battery. Put a volt meter on it and hit the starter. I'm betting it drops voltage.

All of the above. And also check your connections, it's rediculous how little corrosion it takes to make a battery seem bad.

Are you jump starting it by putting both cables on the battery, or are you being a good Boy Scout and grounding to the engine?

A bad engine ground acts just this way.

So does a bad connection at the battery-clamp interface, although that one will also work if clamping to the battery at both terminals.

If I recall correctly, one places the negative jumper lead not on the flat battery's negative post but on some other grounding spot under the hood when jump-starting a car. Perhaps your "good" battery isn't grounded properly.

There's a hard scaly layer that can form on the inside surfaces of the clamps, and on the outside surface of the terminals.
It DOES NOT conduct electricity.
Use a wire brush or other mechanical abradement to remove it.

Bad connection?

I would take the battery out of the car your jumping it with just for kicks.... And try it by itself.

yeah, I'd try swapping out the batteries ... see if the "good" one will start the other car and vise-a-versa

Looks like every one pretty well covered the possibilities.

Using a voltmeter, the "good battery" should show 12.5 volts when fully charged. the voltage should not drop below 10 volts when cranking.

Well, I don't know the ignitions system on that car, but I had a similar experience. The 1972 Capri has a ballast resistor, and a low voltage bypass system that sends full voltage to the distributor when the starter is engage. The relay for the low voltage bypass wasn't working. Car would crank but not start, but if I jumped it, would start every time.

Dunno. Hope that helps somehow.

PROBLEM SOLVED!!!

Thanks for everyone's feedback. There are a few of you who got the right diagnosis. My battery was fine, but the ground connection from the chassis to the engine had gone bad. Once I grounded it to a better spot on the engine, that fixed it.

With the car running, I checked the voltage across the battery terminals and was getting approximately 14 volts.

As usual, this forum rocks!

14+ volts means your alternator is working.

Glad you found your problem and were able to fix it. Grounds are probably the most overlooked area in trouble shooting.