Re: Bogus (?) Oil warning

[steveb@newkla.kla.com (Steven Buchholz)]

> After a hard run, the oil warning light (and don't fergit the buzzer)
> comes on in my '84 4ks at 2050RPM.  What the hell?
> 
> No matter what gear I'm in, outside temp, when the car is warm, at 
> the approximate RPM, BZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ!.  If I let 
> off or speed up, it turns off.   
> 
> It has happened with 10W-40, 5W-50, and 10W-30 oils.  I always use
> Mobil-1.  The Oil pressure does not fluctuate when this is happening, 
> so I don't think it's mechanical.  It also does not happen if
> the car is in neutral and RPM's are 2050...
> 
> Does anyone have a clue???  Why would the oil pressure sender be wired
> to the tach?
> 
... it turns out that it is by design!  Audi had this "cool" idea to try
to help detect problems with oil pressure that might affect engine long-
evity called the "dynamic" oil pressure circuit.  Most cars have an oil
pressure switch that cause the light to come on at some ridiculously low
pressure.  The Audi system has two switches and there is a module that
monitors the switches.  Anytime the low pressure switch is on the warning
light is activated, and if the RPM is above a certain point and the high-
pressure switch is on then it will warn you as well.  

If you see good oil pressure you may have a problem with the switch, or
since your problem occurs at a particular RPM it may be the electronic
module.  Since it sounds like you have a separate gauge, you may want to
disable the dynamic circuit rather than paying for a new switch or module.
Check the wiring diagram in the Bentley to figure out how to troubleshoot
or disable the circuit.  You may actually find a relay diagram that indi-
cates which is the proper module on your fuse box if you don't have the 
Bentley.  I have the manual for the '84 4kS at home ... I can look it up 
for you if you can't find the info elsewhere ... just let me know!

Steve Buchholz
s_buchho@kla.com
San Jose, CA (USA)