Cajun

My '87 S4 has developed an issue with the ABS. The brake pedal grinds and bucks when depressed (and causes the car to pull hard right under braking), and I can't quite figure out what the deal is. I spoke to Roger while the problem was going on, and he mentioned that the problem might be with the ABS...lo-and behold, the other day the ABS light came on, and the car stopped perfectly.

I just had the brakes and rotors replaced. I thought about pulling the fuse related to the ABS until I can track down the problem, however the schematic for the fuses is missing and I have no idea which fuse to pull! Has anyone had this problem? Where should I begin troubleshooting the system?

Also, the A/C blows cold in the rear (my car has the rear A/C option) and lukewarm in the front center, and relatively cool out of the side vents in the doors. I had the system checked two months ago and it was full & holds the charge. Any ideas? It is HOT AS HELL in New Orleans this time of year, especially with black interior.

Any guidance or input on either of these questions is greatly appreciated. I expect to burn up because of poor A/C in my 930, but not in my 928!!!

Marine Blue

It sounds like you have vacuum related issues with your HVAC controls, same problem I had with the 87 S4. Have you checked the vacuum system for leaks?

Cajun

Although I am pretty mechanically inclined, I don't know very much about my 928.

What is HVAC?

Mike Frye

HVAC=Heating, Ventilation, Air Conditioning

AO

Most likely the culprit for your warm air is either a vacuum leak as discussed, or another distinct possibility is a faulty heater valve.

On the '87 I just bought, the valve closes, but warm air still enters the cab (rear is cold). I will be replacing the valve at a total cost of $25.

As for the ABS... sorry, I can't help, but it sounds like maybe a faulty valve in the ABS system. Just a SWAG (silly wild *** guess)

Cajun

Sounds like the valve might be the culprit. Sometimes on the center vents the top vent will blow cold and the lower vent will blow warm.

Where is the valve located?

Thanks for the responses gentlemen...

cold_beer839

I had the same problems recently.

You need to pull the side covers off your center console and vacuum test the HVAC lines to see if you have a bad vacuum pod.

In the meantime, pull your center vent above the HVAC controls and see if your comb flap closes all the way (it is a likely spot for hot air getting past the heater core and into the cabin). If not, just tape it closed until you can replace the vacuum pod that controls it (located inside the dash just to the right of the comb flap). Roger has the replacement diaphragm for $32 for the comb flap. Go in through the glovebox to get to it. It will be tight.

Also replace the heater valve as others have stated above. It is a cheap and easy repair. 928 Motorsports sells a nice metal replacement for about $32 plus shipping. It is located under the air cleaner assembly and takes about 20 minutes to replace. (http://www.928motorsports.com/parts/heatervalve.php) The other 928 suppliers also carry these valves in plastic and metal.

Cold AC is always nice.

Erling G-P

David, can you just yank out the center vent, or is there something you have to loosen first ?

Would like to make the same check on mine, since my AC isn't as effective as I'd like it to be - and I normally get warmer than ambient air through the vent, if the AC isn't on.

Thanks in advance,
Erling

Alan

Go to www.928gt.com and look under the tips section fot the fuse/relay printout for your car.

The HVAC issue could be the water valve (from a vacuum perspective thats the only real possibility for a temperature issue) - so I'd just observe the water valve operation - remove the air filter box - its right underneath. Test it with the ignition on but car not started. With HVAc on - in full cold slider position it should be closed and should be open at full hot position.

It could also be a faulty/clogged AC expansion valve limiting evaporator effectiveness. Cleaning the evaporator may also help...

Alan

WallyP

If you will send me a request via normal email (not thru Rennlist) at techAT928gt.com (change AT to @), I will send you a tech paper on the HVAC system that should help...

ew928

When at the 928GT web site, look for the ABS relay for your 87.
Pull the relay till you get the ABS fixed.
That way you will have regular non-ABS brakes and car will not pull to one side.
With ABS relay removed, the orange ABS fault light will stay on on the dash.

Cajun

Its interesting that you should mention this. After running the car for a while with the A/C on, if I make a sharp or extended right hand turn, COLD WATER pours from under the dash board on the drivers side and soaks my shin and lower leg. Could something down there be clogged? I know that it is A/C related, but I am not sure what I am looking for.

All of the comments above are EXTREMELY helpful, and this weekend I will jump in and figure out the problem...

Jim bailey - 928 International

The ABS relay on the central fuse board is on the bottom row fourth from the right part # 928 615 124 01 . The 928 ABS is a three channel set up one controls BOTH rear calipers , one the left front and one the right front. All the ABS can do is release pressure it NEVER adds pressure . But it is possible , very rare , for one to malfunction and bleed off brake pressure at the wrong time the question is is it a brain problem or the Hydraulic unit. My guess is that it is more likely a brain (control unit 928 618 120 01) issue.

Cajun

Thanks. Will do.

Cajun

What is the best way to determine whether or not it is a "brain" problem?