Ritz928

Hi Guys,

I have a few questions for you all, firstly Im looking at buying a Porsche 928GT 1991 its done just over 80k miles and it looks in real good condition. I have just had it checked over buy a porche specialist and he has noticed a couple of faults.

1. The ABS turns it self off when you power up the ignition???

The owner tells me he has asked a porsche specialist about this issue and was told it was due to the fact the car is not driven enough and the computer goes into shutdown mode and de-activates certain functions. If the car is driven on a regular basis the functions will be re-activated???

2. Also the auto active differential turns itself off when you power up the ignition???

(same as above)

So guys what do you think? To me it sounds a little strange but you never know. Looking into the history the car has only traveled 600-750 miles in the last 3 years and owner has replaced the battery, car is normally kept on a trickle charge.

Just so you know the car is rarely driven in the rain, the A/C all works after a huge amount of money was thrown at a new compressor. The rest of the car looks super, but Im still concerned that I will need to spend serious money on the ABS & electronic diff.

Im keen to hear your comments???

Regards,

Carl

Peter F

It can be any of the relays in the ABS circuit.
If it goes off when the car moves it is probably one of the sensors at the wheels.
But it can also be the PSD that is not working and that can be very expensive to fix since the parts is very costly.
If ABS or PSD doesn't work I think they shut each other down so it may be only one of them not working causing alarm for both.
I had the same issue with mone when I bought it and it turned out to be the PSD pump that was not building pressure.
I payed a lot less for the car with all the warning lights flashing.
My fix in the end was to hunt down a second hand pump unit for 300 USD.
With that in place the ABS warning went away as well.

/Peter

Marine Blue

Might want to start with the relays. Other possibilities are poor contact at your grounds, do a search for the locations of the grounds.

I'm sure others will chime in as well with other possibilities. Good luck and if you get it welcome to club!

Also where are you located?

RyanPerrella

You should have it correctly diagnosed by someone that knows these cars. I think the sellers reasoning to you why it dosent work is BS. "dosent get driven enough." No, there is an issue there wether its as simple as a relay or abs sensor, that would be nice. But you should have it properly diagnosed before hand, unless you can get them to drop the price $2.5K and fix it yourself.

Peter F

With the risk that it is the PSD pump that has been neglected and therefore being toast the discount should be at least 3K USD.
Seems that many owners and also shops are not aware of the PSD system being filled with brake fluid.
Since that is hygroscopic it will absorb water and if not changed every second or third Year it will bring problems to the system.
(it is in the rear wheel well on the drivers side behind the rear cover)
In my case the system ran dry on fluid and the pump had been running dry for probably a long time.

/Peter

borland

PSD Pump Assembly, a rare find on eBay

http://cgi.ebay.com/ebaymotors/ws/eB...m=330035070248

John Speake

Get the owner to pay for a diagnostic tester to be used on the car. This should identify what the real problem is, then a price reduction can be negotiated.

The ABS sensors can corrode in the hubs and crush the senor, damaging it. Pumps also fail, as mentioned above.

Sensors are not too expensive, but it can take some time to remove the old ones.

RyanPerrella

Sterling,

About your mention of the faults showing when a car dosent move an inch, I have a PSD issue when the car is initially started, and hasnt moved. I get the error of differential control out or something to that effect. Yet i notice the PSD light come on when accelerating out of a turn or on wet pavement. I am pretty sure my PSD isnt functioning correctly but if its disabled like my information display tells me, why then do i get a PSD light at all? Are you familiar with this at all?

I had tried once to bleed my psd system but couldnt get fluid out of the lock cylinder, and gave up. I have been told to try to bleed it again which i just havent gotten around to.

Any ideas on these symptoms?

Schocki

Carl,
A faulty ABS Sensor could be the problem already. It is not very likely that two independent system fail simultaneously. Both ABS and PSD use the same Sensor source (ABS Sensor). Before you go any further it would be time to read out the ECU with a JDS-Spanner or a KTS 300. Looks like a faulty sensor to me.

My right rear ABS sensor delivered a non plausible signal one day while driving the car on the highway. ABS, PSD and RDK where shut down immediately. Cleaning of the sensor was the solution. But if your fault comes on before you even move the car than the sensor itself or the wiring is complete gone. The ABS ECU checks the circuits and as soon as you drive it should get speed signals, if these are not OK than you get the fault after you start driving. If the a sensor circuit is missing it shuts down the system even before you move.

BTW what about your RDK??? It also depends on the ABS sensors. Sounds like the ECU is jumped already...

Ritz928

Guys,

Thanks very much for all your comments, as I pretty much already suspected there is a lot more to it then simply driving the car more.

I think with an overall view the owner will either need to drop the price or get the fault properly diagnosed (the second option being the best) as it could be a problem with more than one component.

Cheers again to all you guys!!!!

Ritz928

Schocki,

Funny you mentioned that but the RDK is also intermittant! What do you mean about the ECU having jumped already? Is this in relation to like a checklist where if a fault is located it jumps to an alarm status?

Carl

Vilhuer

RDK is notorious for not working and in many cases wiring to control box is jumped to stop warning coming on at dash. Jump is also done to allow use of non original wheels which do not have RDK sensors installed.

zorbas23x

My RDK gives me the warnig all the time because of the cup1 wheels.I did a flush of the PSD a couple ofweeks ago and it took the new brake fluid with no problem.I am still getting the differential of warning but every time i push the car on turns or on wet road the green PSD light comes on that is working

JPTL

First of all, Ryan's comment above is not opinion, it is fact. Cars 'not getting driven enough' is not reason for these problems. If it were, my '91 GT that, by definition 'isn't driven enough' - in fact is driven half as much as this guy's, is not having any of these problems. Another thing to consider regarding the value of this car beyond mechanical issues is it's ability to pass a state inspection. Although state requirements vary from state to state, I believe that an ABS fault may lead to an automatic failure of a state inspection in some states. That in itself would reduce the value of this car.
If the seller is downplaying the complexity and/or cost of fixing this problem, give the seller an opportunity to fix the problem himself, and make him an offer on the car based on the problem having been fixed.
edit: Oops, I didn't notice that you're in the UK...my comment about states' inspections wouldn't apply.

RyanPerrella

yeah i have heard all kinds of stories from sellers about why this dosent work or that dosent work, it usually NEVER as simple as they can make it out to be.