This car was experiencing dead battery syndrome, so we changed out the battery and same problem, so we changed out the alternator and same problem. Will be driving along and it will quit, if i boost it, it will start and only run while booster pac is hooked up then quit when disconnected. I am in a small country repair garage working on friends cars for fun and do not have a code reader......any ideas??????

The charging system on this vintage is pretty straightforward. Check charging voltages at the alternator output and battery positive terminal, and check for lifted grounds, that will leave a net positive voltage on the negative terminal.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

and 12.9 or so at the battery. i was wondering if it might be a problem with the overvoltage protection relay?

Is it 12.9V at idle???

On my 91 190E 2.3L, the intake preheat manifold draw up the battery. End up that is the preheat manifold relay problem. Replaced it and no more problem.

Hopefully, can give you an idea what problem on your car.

The OVP supplies power to the ECU, and should not affect the reading you are getting. That 1/2 Volt drop between the alternator and the battery is too much. Look for bad connections or a large fuse that has blown.

Steve

__________________
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7