[s-cars] Fwd: Oil Pressure Warning on Auto Check System '91 200TQ

[calvinlc at earthlink.net]

My '91 200tqa reads about 4-4.5 bar when warm and driving at higher rpm,
pegged at cold and rpm, and around 1.5-2 bar when idling and warm.  My S4
gauge is off  as it reads 0.5 bar without the car even running :)

BTW, it is widely known amongst the American musclecar community that the
rule of thumb for safety in oil pressure is approx. 10 psi/1k rpm.  When I
build my engines I always try for 18 psi or above at idle (I like margin)
and about 50-60 psi above 3500 rpm.  Above 80 psi on a prolonged basis and
you start to run into other issues.
--Calvin


-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com]On Behalf Of Huw Powell
Sent: Tuesday, November 14, 2006 6:13 PM
To: Abe Berman
Cc: Keith Franchetti; quattro at audifans.com; Robert Rossato;
Pasqualoni,James E; Perron,Bill; Tom Mullane; s-car-list at audifans.com;
200q20v at audifans.com
Subject: Re: [s-cars] Fwd: Oil Pressure Warning on Auto Check System '91
200TQ



> Can anyone help with this?  Just picked up this great Pearl '91 200
> TQ.  It's a killer great car, but the oil pressure warning on the
> autocheck system comes on between 2k and 3k rpm.  Above about 2800,
> it's on constantly, so on the highway at least it quits beeping.

As I'm sure you know, the first thing with issues like this is a
"reality check."  For instance, if my temp gauge pegged all of a sudden,
the first thought should be "turn it off," not "hmmm, bad sender."

That said, it's nice that most of these cars have an oil pressure gauge
for cross checking.

So, anyway, the system in your car consists of two senders with a total
of three outputs.  One feeds the gauge.  The other two feed the warning
light via a control module thing.  There is a low pressure sender, I
think it triggers below 0.8 bar, and the control unit only worries about
that one below about 3k rpm.  At higher rpms, attention switches over to
the other sender, which I think trips below 1.8 or so bar.

Odds are your sender is futzed, though it might be the CU (it's tall
relay sized).  Try swapping in a borrowed one from a car that works
normally to diagnose.

> Also, I do
> notice the oil pressure guage tends to run a little low, e.g. mid
> range or lower when idling, and just above midrange when engine is
> working or revving.  Could this be the pressure sender?

Do you see 5 bar when cold and revving a bit?  A 1.5-2 bar warm idle is
normal, with pressure rising to 3.5-4.5 or so at revs.  Oil weight and
type can affect this, too.  Running 5w30 in my '57 loader got me barely
perceptible pressure on an Audi gauge, changing to 20w50 got me 2 bar
cold and a solid 1 bar warm.

--
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/
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