jkesselring

Hey guys, I tried this on the engine/tech board and only got one response. That's when I realized that I was a moron and posted on the wrong board.

Alright guys, here is a tough one for you. I have tried everything I can think of and still have had no luck. The car ran fine then the car had starting problems so I eventually replaced the battery. The car ran great for 3 or 4 months and then the car was dead one morning (I think my GF left the dome light on). I jumped it and it ran fine for a month or so. I didn't drive it this last weekend and Monday morning the darn thing was dead. This is the problem, the car runs great if the GF drives it every day (10 miles round trip to work), but if the car sits for 2 or 3 days it is dead. Here is what I have done: I tried the trick of disconnecting the neg cable and hooking a test light between the neg batt cable and the neg post, the bulb lights, but goes out completely after only 3-4 seconds (I think this is the computer). The batt voltage at rest (car off) is 12.17v. When the car is first started it has 14.8v at approx 2000 rpm after 5 minutes or so this drops to 14.0v. When the car is started the voltage drops to 8.7v when the starter engages (though this was after the car was dead and had only charged for an hour or so). I touched the multimeter to the pos terminal and the power wire on the alt and the meter read .40v and I tried touching the neg terminal and the alt case and the meter read .03v. I also stretched the meter from the neg terminal to the neg cable (disconnected) and the meter showed 10.8v. I consider myself pretty good with auto electrical systems, but this damn thing has me whipped. I don't know what else I can do. Any suggestions would really help. The next step is to drop a match in the gas tank. Thanks in advance for any help you can offer.

jkesselring

BTW the car is an 86 IROC with the 305 TPI / 700R4 combo. It also has power windows and locks and antenna (has been converted to regular antenna). I also disconnected the power hatch pull down. These problems have been happening for 3 years and a new battery usually cures the problem for another 3-4 months (exide batteries) and the parts store is probably sick of me returning them. Thanks again guys!

1MEAN92RS

So it's charging okay at idle??? Upon reading it the first thing I thought was it could be the voltage regulator, but if it's charging okay at idle then I dunno. What does it read if you have the headlights and heater fan on at idle?

The second thing I can think of is does it seem to start okay? Does it sound like your starter is dragging? Sometimes when starters go bad they create a slight dead short and will drain the battery slowly over a couple of days (this was the case on my brother's '88 IROC Z28 last month).

Later,
Harry

Danno

First thing to do is to trickle charge the battery. Based on your voltage reading the battery is on the low side of capacity. An alternator will NOT replace a good overnight trickle. It could be as simple as a bad battery no matter how new it is. One severe discharge can permanetly damage a lead acid battery. Use your meter set to amps, disconnect either battery cable and then measure parasitic drain with the meter in series like the test lamp. When you do this make sure doors are closed, and hood light if equipped is disabled-everything must be off. Standby or parasitic drain should be less than 15Ma, or .015 amps. Almost anything in the car causing drain will lift the parasitic value 50Ma or higher, then you need to start pulling fuses to isolate. If that's OK and the alt is 14 or higher have the battery tested. I have worked a lot with L/A batteries over the years, they can be funny animals.

jkesselring

Thanks guys,
The starter is relatively new and has no trouble starting the car so I don't think it is dragging. On the bad battery comment, I have replaced the battery about 3 times so unless all three were bad, I don't think that is the problem. Thanks for the milliamp test that you recommended. I will try that this weekend. Any other ideas out there? I have some time this weekend so I want to really crank on it and get the problem solved! Thanks again guys, YOU ROCK!!!