Bad battery, bad alternator, or other?

SpeedracerIndy · 09-10-2007, 12:55 PM

I'm trying to fix a problem with my dad's 88 Carrera. The car will not start when it is left sitting over night. After about one week, there will not even be enough juice left in it to work the clock. However, if jump started, it will run fine all day and start fine when left sitting in a parking lot for several hours. I have a pretty nice battery charger that will test the alternator and battery. When I hook that up, it will tell me that the alternator is bad. It will charge the battery at 2, 10, 20 and 35 amps without any faults. When I checked the voltage at the battery with the car running, I get 13.59 volts. When I checked the voltage with the car off, I get 12.59 volts. The radio just recently stopped working too, although I think that this is unrelated. I'm thinking that the alternator is working fine because I can drive the car around all day and it starts right up every time. I didn't think a bad alternator wold cause a slow drain on the battery over night. Can someone help me figure out what could be the problem here? Thanks in advance!

Rot 911 · 09-10-2007, 12:58 PM

The charging is a little low, but still acceptable. What is the voltage at the battery when the car has sat overnight? You could either have something draining the battery or a bad battery that will not hold a charge.

SpeedracerIndy · 09-10-2007, 01:02 PM

I just picked up the car today and started poking around, so I'll have to check in the morning after it's had a chance to drain. I'm thinking that maybe the radio does have something to do with it now. I drove it a few weeks ago, and the radio was emitting loud static, then it just stopped working. It has a factory Blaupunkt (sp?) radio and factory (I think!) Blaupunkt EQ/amp under the passengers seat.

SpeedracerIndy · 09-12-2007, 04:39 AM

I charged the battery fully, and let it sit all night. After a night of sitting the battery showed 12.85 volts. Now I'm confused.

Porsche_monkey · 09-12-2007, 05:14 AM

So after sitting all night did the engine turn over?

SpeedracerIndy · 09-12-2007, 06:08 AM

Yes, it turned over strong as ever. In fact I drove it to work today.

I charged it up to full yesterday, drove it to dinner, then parked it over night. After one night, it doesn't appear to have lost any charge. I think my dad might have underestimated the amount of time it takes to loose its charge. He hardley ever drives it. It probably sat for more like a week the last time he tried to start it and it wouldn't start. When I picked it up the other day, it was dead as a door nail. The clock wasn't even working. So, does this mean bad battery or a slow leak? If slow leak, how do I go about tracking it down?

Porsche_monkey · 09-12-2007, 06:24 AM

You need to measure the current draw with the ignition off and doors closed. Remove the + terminal and use a multimeter set on 'amps' to measure the current between the + terminal and the + cable.

Post the result here. You should only be drawing current for the clock and radio memory with the ignition off.

Grady Clay · 09-12-2007, 06:35 AM

Unless the battery is new, I would summarily replace it.

I would also disconnect power to the radio and amp. Actually the radio needs to go in for service.

I agree with Kurt that the charging voltage is slightly low but still acceptable. I wouldn’t do anything with the charging circuit until you have a new battery.

There are also all the normal things to check; ground straps (particularly transmission-to-chassis), battery connections and the big red wire at the battery B+.

Best,
Grady

SpeedracerIndy · 09-12-2007, 07:13 AM

Great! Thanks for the advice guys. I'll test the amperage draw tonight when I get home from work.

I put the battery in the car probably 3 years ago. It says it was manufactured in 2002. It probably only has 5,000 miles on it at the most. I guess that could be why it went bad, from not being used. I bought a battery tender for the car, but it might be too late for that.

rick-l · 09-12-2007, 08:16 AM

Quote:

Originally Posted by PBH

Remove the + terminal and use a multimeter set on 'amps' to measure the current between the + terminal and the + cable.

It might be safer to remove the "-" terminal off the battery. Your meter won't care.

My 88 draws 90 mA. It has a high tech (for 1988) Clifford alarm and a similar vintage 10 disc Sony CD changer.

SpeedracerIndy · 09-13-2007, 02:29 PM

Well, I tried hooking up my meter in line with the battery (to measure amperage) with nothing on, doors closed, etc. It fried my meter in a matter of seconds. It started smoking, then blew the fuse on the meter. Seems like it would have to be a pretty big current draw to do that, or something with much higher resistance than my meter. Any ideas? As soon as I get another fuse for my meter, I will try disconnecting the radio/amp and try to get a reading again.