I have been searching for a few weeks and can't seem to find the answer so I am taking to posting. Sorry if this is a duplicate. On my olds, it is a 70 delta 88 convertible with 455 engine. I have replaced the voltage regulator which usually is the issue and also had the battery checked which it tests fine. If I use a voltage tester what should be the running voltage at the battery amd at the alternator before the voltage regulator? I am trying to pinpoint the issue. When I drive it and stop and turn it off it doesn't want to start. When it sits I have a disconnect on it. Anybody know what readings I should get and when I should consider the alternator needing to be replaced or rebuild it if the voltage is below a certain level?

 

Sounds like a drain or draw if you have to disconnect the battery so you can use it again!

Unhook the negative side terminal and hook your meter or test light in series, with all doors closed, radio and key switch off. If you have drain your meter or light will show it.

Pat

 

I have tried the test light and nothing. I put the disconnect on think there was some sort of draw but there isn't. The battery currently is at 11.98 volts, and when i try to start it it will start to turn the engine but then nothing, it seems like it wants to start but just can't kick it over.

 

12V is too low for a fully charged 12V battery, so something's not right.

The alternator should put out somewhere between 13½ and 14¼ volts (maybe up to 14½, especially if you don't take long trips).
You should have essentially the same voltage to ground when measured at the battery (+) post or the alternator output post, and also at the horn relay post.
You also need to be sure that all of your battery connections and grounds are shiny and tight.

- Eric

 

Make sure the belt is tight.

 

What is the battery voltage when attempting to engage the starter?

We used to watch the headlights while cranking. If the lights dim out that means the battery is unable to provide the voltage required when the starter load is applied. Faulty battery or starter.

Can you get your starter out and have it tested?

You can peek inside the starter and see if it is obviously worn out, after you remove it... if you have some degree of mechanical skill. Worn out brushes are pretty obvious.

 

If there is only 11.98 volts on your battery there is no need to test the starter. The battery is at 40% or less. It will exhibit slow or no cranking there.

 

It's my understanding that each cell of the battery is 2.1v. You have six cells on a 12v battery so fully charged it should read 12.6 volts

 

I agree that this statement with a no load voltage of 11.98 "does not compute". I'd start looking for another battery to see if it solves the problem.

 

My wife's Toyota would not crank a couple years ago. I tested the battery and it tested fine. we ended up taking it to the Toyota dealer where they replaced the starter, starter relays, onboard computer and spent 3 days diagnosing that the car had a bad battery. Always eliminate the simple things first. As others have said, if the battery voltage is less than 12 Vt there is an issue. Good luck in finding the problem.

 

If you have to disconnect the battery to keep it from discharging, you may have a bad diode in the alternator.

 

I guess this brings up the question of what does "tested" mean?

Measured the specific gravity of the electrolyte?
Performed a load test?
Or simply measured the open-circuit voltage?

 

Correct about the load test. Even a weak battery will often read 12v across the terminals, but won't crank the motor over.

 

A closed (fused) contact in the voltage regulator will also discharge a battery overnight.

 

Load test and open circuit voltage. We did not have access to a hydrometer at the time. The unusual thing was lights burned bright, and all electrical circuits seemed to work normally. I believe the battery shorted internally. It happened during a ride on a ferry. I believe the vibration of the ferry effected the battery.

 

Yeah, that happens a lot with the off-road vehicle out here in the rocky desert - the vibrations break the plates loose and they short out. That is why the AGM batteries are so popular.

Optima batteries used to be the ticket but over the past couple years their quality has gone downhill so badly they fell out of favor.