forum.audiv8.com Foren English Audi V8 Forum Electrical, hydraulic, or tensioner problem?

I had an interesting drive in the rain today, and then everything slowly went dark, and a little heavy...
After 400 miles, rain stops play.

It started out as what I thought might have been a partial loss of output from the alternator.
First, the voltmeter dropped under 12volts, and slowly crept down, eventually registering 8volts.
Keeping the RPMs up helped a bit.
Surprisingly, the ABS stayed functional until the terminal volts dropped a long way below 10volts, and of course, once it tripped off, it was off for good.
The Battery light did NOT come on solid, though. It was flickering at 1/4
intensity, as was the CAT light. Windscreen wipers initially ran fine, and the engine was running for a good long while.

I managed to nurse the car to some convenient services. The alternative was to stop on the hard shoulder in the miserable conditions. An of course, that was still an option if all went completely wrong.
When I pulled off the motorway, the steering was very heavy, and notchy, as if the pump wasn't running correctly (belt loose?)

So-
Seized Alternator
Seized PS pump

The car started a few minutes later, and seemed a little better for a while, before finally dying on it's own.
While it was running, the belts were ok, no noises, no squealing. I guess the poly belt is a pretty good grip.

A whole hour later, the car started normally, and all was fine, except volts still low, at about 10v, for about 30seconds, and then it all decayed rapidly, and the steering went heavy again.

does the battery pilot lamp light up when you switch on ignition?
I don't think, that the hydraulic pump is the cause, it's obviously the consequence.
What makes you sure that the aux-belt is tensioned seriously? It doesn't mean anything, if you can't hear it squealing, especially when the belt and pulleys are wet.
I guess it is a matter of drive belt tensioning or it's condition. The temporarily break down of the power steering is an unambiguously sign.

The Batt light comes on solid when igniton turned on, so that is normal.
I'm thinking alternator failure, although I'm hoping it's the belt, but there is certainly no slack in it.
I have 2 spares, but all 3 are new- this one was installed when the engine went back in, last year, this time. At least 12kmiles

When time allows, I'll take it off, and check out all of the pulleys, etc.
The

Marc,

do you have Servotronic? The only sensible way how only the alternator could be broken is that the valve control of the electronically regulated power steering valves stops operating when power drops under a certain treshhold. If you don't have servotronic, then I'm with Tim, it's something about the belt.

Bastian

I start disagreeing with myself but first: Do you know, that auxiliary drive belt for the V8 is available in three different dimensions? The possible lengths are 2433, 2460 and 2480 mm. I mention this, because I guess you've made a "few" modifications on your car and I'm searching for the relation between the fault an the weather conditions. Due to that, the moisture and an over long v-belt might cause your problem.
There is one simple way to check the tensioner: Just pull the belt on it's long side (at the bottom). You should feel significant resistance and see the tensioner lever moving without jamming.
Now to my doubts:
Bastian has mentioned the Servotronic steering rack- this was wise!
If the steering ECU has got no (or not enough) electrical power supply, the steering support will collapse. So the alternator might be the cause in deed, because you've written, that the voltage rate was decreasing steadily.
If the pilot lamp is flickering during acceleration that will be a sign for worn carbon brushes.

I think like Tim...

My car normally it's all ready by rainfall, but if the snowfalls is to heavy, the streets are high covered with snow, sometimes the same problem like yours... without squeaking too...

Do your car has the "Motorunterschutz" (i think you know) ?

Post deleted by Mark Hanman

Servotronic is a speed dependent support regulator. It makes your steering rack been engaged easier, the slower you ride and conversely.
It is directed by an own ECU. If this ECU's got less or no power supply, power steering support will collapse.
You can identify Servotronic by a little block fitted to the governor head of the steering rack. The block is equipped with little wires an a jack. No wires and jack at the rack - no Servotronic.