Weird intermittent low voltage warning (90GT).
09-28-2011, 05:20 PM
#16
Racer
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Didn't have much time to fix the problem lately, but there's an update either way - the car has developed some new behavior:
1) Dashboard voltmeter does not show the voltage drop anymore, although the ABS light (and it looks like the PSD light too), plus the "Batterie strom sparen" warning still go on when going left with a fairly high side g-force.
2) Alternator does not start charging until I rev the car to ~3K.
The ABS/PSD system is rather complex to pinpoint the exact problem, but maybe the second symptom can help isolate the issue?
1) Dashboard voltmeter does not show the voltage drop anymore, although the ABS light (and it looks like the PSD light too), plus the "Batterie strom sparen" warning still go on when going left with a fairly high side g-force.
2) Alternator does not start charging until I rev the car to ~3K.
The ABS/PSD system is rather complex to pinpoint the exact problem, but maybe the second symptom can help isolate the issue?
09-28-2011, 05:50 PM
#17
Under the Lift
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Guess what? The ABS power lead is unfused. 
I would unfasten, clean and retighten all the major ground points if you haven't done that. Good idea regardless.
If the alternator does not charge at idle something is broken in the exciter circuit. It passes through the 14-pin connector near the jump post in the engine compartment. It might be worth checking the condition of that connector and the wire harness attached to it. It is common for the insulation on the wires to deteriorate near this connector and create quite a mess. The outer harness sheath is usually quite age/heat hardened and brittle, and the wires inside even worse.
I would unfasten, clean and retighten all the major ground points if you haven't done that. Good idea regardless.
If the alternator does not charge at idle something is broken in the exciter circuit. It passes through the 14-pin connector near the jump post in the engine compartment. It might be worth checking the condition of that connector and the wire harness attached to it. It is common for the insulation on the wires to deteriorate near this connector and create quite a mess. The outer harness sheath is usually quite age/heat hardened and brittle, and the wires inside even worse.
09-28-2011, 05:55 PM
#18
Electron Wrangler
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I think the PSD/ABS is likely quite unrelated - when there is a warning these systems are disabled.
Seem you have a fault with the alternator exciter curcuit - I'd fix that first since its a known issue.
Other things I would do for this are:
Check (clean/tighten) the wiring connections at the jump post and on top of the CE panel, at the starter and on the alternator.
Replace the ignition switch.
I agree with you it isn't the interior lights and it probably isn't a short - its more likely the alternator kicking out and/or a loose (open) connection. It possible it couls also be ground related - I'd especially check the engine to chassis ground.
Alan
BTW - there are many many things not fused - at all - on a 928
The path from the battery to the starter and alternator, the whole path to the front jump post and to the top of the CE panel, the fan final stage feeders, the ABS main supply for the hydraulic pump, the ABS supply for the brake circuit actuator solenoids, the EZK ECU and the Disable Ignition relay that feeds the LH ECU... its a horribly long list which is why you always need to remove battery power when working on the car electrics...
Seem you have a fault with the alternator exciter curcuit - I'd fix that first since its a known issue.
Other things I would do for this are:
Check (clean/tighten) the wiring connections at the jump post and on top of the CE panel, at the starter and on the alternator.
Replace the ignition switch.
I agree with you it isn't the interior lights and it probably isn't a short - its more likely the alternator kicking out and/or a loose (open) connection. It possible it couls also be ground related - I'd especially check the engine to chassis ground.
Alan
BTW - there are many many things not fused - at all - on a 928
The path from the battery to the starter and alternator, the whole path to the front jump post and to the top of the CE panel, the fan final stage feeders, the ABS main supply for the hydraulic pump, the ABS supply for the brake circuit actuator solenoids, the EZK ECU and the Disable Ignition relay that feeds the LH ECU... its a horribly long list which is why you always need to remove battery power when working on the car electrics...
