At 11:36 AM 5/1/00 +0200, you wrote:
>I'm considering to change the brake fluid on my '85 928S euro AT with ABS, to silicon DOT 5 brake fluid. Any comments on this are welcome.
DON'T! Porsche, along with most auto manufacturers specifically reccommends against using DOT 5 fluid. There are a couple of problems with this fluid. Silicone fluid entrains air very readily, and it is very difficult to get this entrained air out of the fluid. This makes it difficult to effectively bleed the system, as the entrained air creates bubbles at every high spot in the system.
Silicone fluid is not hydrscopic - that is, it doesn't absorb moisture as does standard brake fluid. While this sounds like "a good thing", it isn't. Any moisture int he system works its way to the lowest spots in the system as beads of water - this results in rust pits in the calipers.
>Second, my car is experiencing a starting problem. I will never start up the first time. The second time it will almost start always after +/- 1~2 sec's. Recently i noticed the on turning the key the first time the fuel pump won't run for a few moments. When i just turn the key again without starting the car the pump still won't run. After i crank it over once, the pump will run when i turn the key. I assume the problem i related but i don't know how to fix it.
All cars with electric fuel pumps need some type of safety system to prevent the fuel pump from running when the engine isn't running. Porsche elected to do this electrically. The pump will only run for about two seconds when you hit the starter, then shuts off until either the engine cranks (giving a minimum rpm input) or you hit the starter again.
The engine needs the proper fuel pressure to run, and rather than depend totally upon the pump for starting, there is a fuel check valve located in the fuel pump outlet that is intended to hold the fuel pressure at a minimum level while the engine isn't running. These check valves sometimes fail, causing the condition that you describe.
Check our website < www.928gt.com > for tips (including photos) on replacing this check valve.
Until you replace the check valve, try hitting the starter a couple of times for only two seconds, then try to start the car normally.
>Thanks for any help on this.
>Hans Pijfers, Holland