boerge

Hello,
First, is there a place with info for the 928, just like there is Clarks garage for the 944?

My tire pressure warning system on the 1989 GT, is telling me that my two rear tires are low on pressure. It is indicated all the time from startup.
Checking the tires shows everything normal.
What are the main problems with the tire pressure monitor system?
Is there an easy fix here?

I have original 16" Clubsport rims.

Thanks
Boerge

Bertrand Daoust

The main problem with this system is that it's really too sensitive to be all that useful.

A do it youself fix is to unplug the connector (leaving the RDK computer disconnected) and put a jumper between pins 2 and 13 on the harness connector.

That's what I did on my car. No more false low pressure warnings!

Marine Blue

What pressures are you running at the rear?

RKD in OKC

The tire pressure monitors on my 90GT worked GREAT!, But you absolutely have to set them according to the manual. ie fill to low pressure, drive around the block, fill to higher pressure drive around the block, air back down to set pressure of 36 front 44 rear on 90 GT... The low and high pressures are different for front and rear and it's been too long for me to remember what they were.

Several time my local garage tried to reset the sensors using the hammer and rolling the car only a few feet. They ALWAYS falsed unless set according to the manual.

GregBBRD

And don't forget to hop around in a clockwise direction, on one foot, while doing what the manual says...

boerge

Thanks, great answers, I didn' t know the procedure on how to fill the tyres, neither that it was so sensitive..

Does anyone happen to know low/high pressures front/rear, for use in the filling sequence?

If I still can't get it right, I'll go the "jumper-fix" way.

Regards

Boerge

RKD in OKC

Try 6 psi below he set pressure, then 6 psi above the set pressure with the set pressure for fronts being 36 and rears 44. I'm pretty sure that was the pressures on my 90 GT.

bigmac

Boerge, My 90 S4 was so sensitive that every time a weather front came through the warnings went off.

I had them disconnected.

jcorenman

Isn't it also possible to fit 36# sensors (used in the front) to the rear wheels ? I understand that this is not a simple or cheap suggestion. But personally we're much happier with 36# all around, car handles better and the rear tires wear more evenly. It also seems that most folks here prefer that.

RKD in OKC

Like I said before, in the two years I drove my 90 GT when I set the tire pressure like my manual said I only got warnings when the tires were actually low, no matter the weather. And they saved me from coming out to a flat tire twice. If I remember right the warning went off at 30 psi and I was able to make it to a tire shop to get the screw removed and the tire plugged.

Procedure...

Air front tires to 30 psi rear to 38.
Drive around the block not exceeding 15 mph
Air the fronts up to 42 rears to 50.
Drive around the block not exceeding 15 mph.
Bleed fronts down to 36, rears to 44.
You are done.

And though I thought the rear seemed too high, I didn't have the abnormal center of tread tire wear typical with too high of a pressure.

boerge

Thanks for excellent help on this.
I thought I already had a high pressure on my rear tires, but by checking, they were 38 psi, so I filled them up to 44, and alarm is gone. Cant blame the germans on this one..
The only thing is that 44 seems very high, especially in the rain...
It's just the feeling when you get rid of these alarms, I'll sleep good tonight.
So case closed for me.

Thanks again.

Boerge

damonoresky

How exactly does this monitoring system work? The PO of my car said they rear sensors were damaged and I have the warning lights on all the time. I haven't tried the above procedure, maybe that will work but none the less, what can be damaged when removing the tire here?

Jim Chambers

Where is the RDK computer/connector located?

Rob Edwards

The RDK computer's up under the dash above your left foot- if you had to R&R the hood cable or remove the clutch pedal it's the one making your life difficult.

TheoJ

Extract from the 1990 service info manual:
Each wheel has a high frequency sender (2) on wheel carrier (1) . High frequency senders are connec-
ted with the RDK control unit. Each high frequency sender produces an electromagnetic field on the
sender end, which is directed toward the diaphragm pressure switches . Diaphragm pressure switches
pass the high frequency sender as the road wheel turns. In this manner the oscillating circuit of the
diaphragm pressure switch is brought into the sphere of influence of the high frequency sender's elec-
tromagnetic field .
Inductive coupling is produced between the high frequency sender and diaphragm pressure switch .
Current flows in the pressure switch oscillating circuit when the tire pressure is correct (pressure
switch oscillating circuit made), since the oscillating circuit acts as a consumer because of the cir-
cuitry design . This additional power consumption is recognized and processed into voltage pulses in
the RDK control unit. These voltage pulses are compared with the wheel speed pulses of the ABS
control unit .

I agree that the RDK is a perfect device if only it could be adjusted a bit. Much is based on the trigger point of the wheel sensors. When I have more time I want to have a look at this unit.

For those of you who want to ditch the RDK: don't. Besides the safety aspects, the RDK also offers a monitoring possibility of the ABS sensors through the RDK diagnostics over the diag bus. Just hook up the diagnostic interface and off you go. Best way to see if the sensors work all right.

regards
Theo