Hi guys.

'88 Daytona, 2.0L (?), turbo, 170k...

I didn't drive my car for a long, long time, then when I went out to crank it up, the battery was dead. Like absolute zero.

Ok, fine-- I figured it was just from sitting there forever. So we jumped it, drove across town, then shut it down at the gas station, and when I went to start it again, it was the same thing-- absolute zero charge, not even a hint of an interior light...

OK, FINE-- so now I figure the battery itself was just toast. Checked my receipts; yup, 2-year warranty battery that was now five years old. So I got a new battery, starts right up, bingo. Then, t'other day, I go out to start it up and it's the same thing-- almost absolute zero, (just a few mere photons from an interior light).

OK FINE!!! So now I figure it was the alternator/charging system the whole time, maybe. So here I am with a dead battery and I want to diagnose this thing correctly this time.

( *** sigh *** )

Question: How can I be sure that it's the alternator rather than, say, an electrical leak somewhere, or some other part of the charging system?

 

It sounds like your alternator/charging system is working, or you shouldn't have been able to drive across town. The car was running off of the alt. current and ignoring the dead battery essentially.

It sounds to me like you have some sort of drain on the battery when you stop the car like a radio wired incorrectly, or an interior or hood light??

You don't say how long it sat with the new battery before you went to start it again, but if it was a few days or more it sounds like a slow drain. If it was overnight, it might be a larger drain...

As far as finding out if your charging system is bad, if you go to a batteries plus or similiar, they will usually test your charging system for free. If this isn't possible, find a friend who has a volt meter and check the battery voltage before and after starting your car. The voltage will probably be around 12 volts on a good battery when it's not running and it should jump up to at least 15 volts (probably more) when the car is running.

Hope this helps,

josh

 

Ah. I guess you're saying that a car with a dead battery AND a dead alternator would not run... EVEN when jump/push started? Interesting; hadn't occurred to me.

Dern it, that makes things complicated. Nothing had been done to the car for a long long time, (no new radio, etc), so if there is an electrical leak, it must be something really sneaky; something that's rusted through finally, or something like that... Oh, bother!

Yes, quite a few days.

I've never heard of Batteries Plus, here in California... A car shop just for batteries?!? Well I can ask around for who might test me for free, but I've never heard of such a thing like that either. Maybe that's a cold-weather part of the country kind of service?

I know I sound like a ditz, but I actually have done alot of my own work on the car; I have a nice digital VOM too. Although, the car itself has a volt meter for the battery. Don't recall ever having seen it climb above 12 ever... Maybe it's not so accurate? Anyhow, I can look for a jump on starting as you describe.

Well... kinda!

Just kidding, thanks alot. I was worried it might be a leak-- tracking that down is really gonna be a bear...

 

Autozone, PartsAmerica, Advance Auto, places like that usually don't charge to test the systems...

 

"Ah. I guess you're saying that a car with a dead battery AND a dead alternator would not run... EVEN when jump/push started? Interesting; hadn't occurred to me."

[b]The fuel pump needs electricity to pump the gas and the computers among other things need electricity to operate, so if the battery was completely dead and the alternator wasn't working and supplying electricity, your car wouldn't run. Back in the day of old school muscle cars that were carb'd and didn't have computers, they could after a jump as long as you didn't shut them off, but newer cars can't.[/b]


"Although, the car itself has a volt meter for the battery. Don't recall ever having seen it climb above 12 ever... Maybe it's not so accurate"

A car voltage meter should go above 12 volts when the car is running if it's calibrated correctly, but I wouldn't use that guage as final anyway. Definitely use a voltage meter across the battery before and after you start it to compare the difference in voltage. It will be higher than 12 volts if the alt is working properly.

Yes, batteries plus is a battery store (watch batteries, common batteries, r/c car batteries, computer batteries, car batteries, etc.).

 

Charge the battery fully,put a meter across the posts and crank it,the voltage should drop but come right back up,if it does not the battery is weak.
Again charge or jump start it and check voltage across the posts,it should be about 13+ to 14+ volts,if it is,turn on accessories(lights,radio,ac/heater and ?)and see if it effects the running and charging,if either the voltage is lower or the running and charging changes some,check alternator and charging circuit.

 

Thanks everyone for the help.

I got a mini-charger ("for motorcycles, etc"), and left it on when I went to work, (9 hours), and it was 11.7 V if measured instantly, or up to 12.3 V if I left the VOM leads connected for awhile, (the reading climbs after awhile, I guess because it's a battery?)

Stuck it in, the car fired right up. Running, I measured 14.2 V, so there was a definite bump happening.

I wanted to follow the advice given and drain amps, so I turned the lights on... and they wouldn't pop up!! They're those "pop-up" lights; if you're reading this forum, I guess you probably know that. Well the yellow fog lights came on, but not the main lights. Weird; never happened before.

Anyway, I shut down and disconnected the + cable, and inserting the VOM between post and cable, I read 0.010 amps leaking, with no interior lights, (and not the hood light on either). Unless I'm confused, that's 10 milliamps.

Doesn't seem like much, but... I guess maybe that's the culprit?

Bother! Any advice on how to track that down? I can only think to take out a bunch of fuses, see if it still leaks, and then... ?

 

That amount is probably memory drain(radio,computer),pull the fuses for each and check.
Did you check to see if the battery voltage came back up after cranking(but not starting the engine(disconnect and ground coil wire)).Voltage will drop but come back up within several seconds.
The 14+ volts charging is good but what amperes is the alternator putting out,thats why I suggested turning on ALL possible accessories(lights,ac/heater,radio,?)on together,ampere output is lowest at idle.

 

OK, I guess I have bad news for myself; I started with the Las Vegas test:

I started the car and turned on every interior light, the radio, the fog lights, the interior fan and the hood light-- the voltage across the terminal posts was up to 16V or so.

Shutting down, it read 13V directly after that.

Then I did your cranking test-- disconnected coil from distrib, crammed that lead onto the frame, and cranked the engine. Within five or ten seconds, the battery was "dead"-- the starter was having trouble going round even once or twice. Of course, I can't say that the battery was fully charged at the beginning of these experiments-- probably not; probably just enough to crank it good. My little battery charger doesn't tell me how charged the battery is.

I don't have anyone else here so I couldn't do the other thing you suggested of measuring volts while at the same time cranking the engine.

Uh oh?

 

Here's an article on charging system diagnosing for 2.2 and like mopars in case it helps...

http://minimopar.knizefamily.net/charging.html