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  #11  
Old 09-26-2005, 11:12 PM
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Hulk Hulk is offline
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OK, I think my problem may be something else...

This morning my 80 would not start after sitting all weekend. I put the trickle charger on it, and left it for the day. It was a very nice day for driving my topless 40 anyway.

I bought a $20 multimeter from Sears. Tonight I did some measurements:
Battery with vehicle off: 12.34 v
Battery with vehicle on, idling: 14.56 v
Battery with vehicle on, headlights on, car stereo blasting, A/C on super cold with fan blowing on high, idling: 14.55 v
So I'm thinking that my battery is probably OK (it's an Optima red top, only 1 year old). And I'm thinking that my alternator is doing its job. So something is probably drawing current when the vehicle is off, and now I need to discover what it is.

What next?
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  #12  
Old 09-26-2005, 11:37 PM
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Rzeppa Rzeppa is offline
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Take that nice new multimeter, disconnect the red test lead from volts/ohms and connect it to amps. Set the range to 200mA. Disconect one of your battery leads. Connect the multimeter between the battery post and the disconnected lead. A current draw of a couple, maybe tens of milliamps will be normal draw from stereo clock, etc. Several hundred milliamps means trouble and could explain battery discharging while sitting. If current draw is normal, then your red top may be bad, not holding a charge. I have a yellow top which exhibited the same symptoms. Rare, but it happens. Less rare, you have a faulty load such as your ECU.

You certainly want to eliminate your battery cables as the source of the problem. I assume you jump start at the battery end of the battery cables. Usually, if the cables are bad, it won't start this way, but not always. Another good test is to prick the top of each battery post with your test leads while measuring voltage while an assistant cranks the engine. If the voltage drops very low, say under 11 volts or so, it is almost surely a faulty or discharged battery. You can repeat the test with the positive lead at the starter post and a chassis ground to see how much different it is due to voltage drop from the battery cables and associated connections. You shouldn't see more than a half volt or so difference.

At least you know your alternator is good. Those numbers are fairly typical, maybe even a little high. 13.8-14.2 is more what you want to see, but 14.5 shouldn't be too bad. Overcharging due to too high regulator output can shorten battery life greatly.
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  #13  
Old 09-28-2005, 12:09 PM
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Jeff, thanks. I'll work on this some tonight.
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Old 09-28-2005, 05:10 PM
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Matt, one caution on checking the parasitic draw (amps) make sure everything is off and the key is out of the ignition. Dome light on = blown fuse in meter. No big deal, but you just have to hunt down another fuse. The spec from toyota is 40-45 milliamps or less with everything off.

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