Ford Taurus' Flat Battery

courtesy of Bob, The Auto Answer Man

Hi Bob,
I have a problem with an intermittent flat battery on a 1995 Ford Taurus. Here are some numbers. Measurements were made with a DVM.

Battery Voltage (normal charging, engine running) 14 to 14.5 Volts
Battery Voltage (engine off) 12.7 to 13.2 Volts
Typical current drain (engine off) 7 mA

The 7 mA is probably maintenance current for the various computers (ECMs). It's also not nearly enough current to drain the battery overnight. Yet, this is a recurring problem. If the problem were a "hard short" or a solid "resistive short," I could troubleshoot this with a current meter, by pulling fuses and watching when the current stopped flowing, but that won't work in this case. I have removed all the interior lamps (65 mA each), and the problem is continuing. I am beginning to suspect one of the ECMs is behaving badly, perhaps turning lights on when no one is near the car. Since there's more than one ECM, it would be nice to know which one has gone bad. There's no point in replacing the ones that are okay. Any ideas how to troubleshoot this one? It's a new battery, so that's not likely to be the problem.

Hmm, it may be more simple. It simply could be a bad cell that is shorting or not holding a charge. Did you run a SG test on each cell (specific gravity)? This will tell you if a particular cell is having a problem. There may be some build up of sulfur on the plates). Be careful, though, when checking as it is acid and can cause harm if misused.
Good Luck!
Drive Safely!
Bob, The Auto Answer Man

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