924Board.org

[xpernet]

Hey guys!

I have just fixed a vacum leak in the car, it was a broken pipe behind the throttle body. Anyhow the car was great untill i decided to hit the brake pedal while at idle, and suddenly i hear this hissing sound from under the dashboard and the car starts to stall, untill i hit the gas pedal. Help!!!

And whenever i rev the car from under 1000 RPM the car seems to stall, if i quickly hit the pedal, but if its above 1000 RPM there is no problem. Can my fuel pump be making some problems?

Also when i turn of the car, i hear this little hissing sound, again from underneath the dash, that suddenly after 4 or 5 seconds burst into one short, yet loud hissing.

I am getting really annoyed

Thanx in Advance !!!

xpernet
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1977 Porsche 924
Sunroof Delete
Megasquirt II EFI & EDIS
Carrera GTS / 944 Body

"If one does not fail at times, then one has not challenged himself." Ferdinand Porsche

[Paul]

Check your vacuum booster (behind the brake master cylinder) by removing and plugging the vacuum hose running to it. If this solves the problem (caution you will have to push much harder on the brake pedal to stop the car), you may have a leaking booster or a failed check valve.

[xpernet]

thanx, ill check that later on. But before i mess around, is there a picture of it ???

xpernet
_________________
1977 Porsche 924
Sunroof Delete
Megasquirt II EFI & EDIS
Carrera GTS / 944 Body

"If one does not fail at times, then one has not challenged himself." Ferdinand Porsche

[xpernet]

I almost forgot. When the car isnt running, the pedal is solid, but when i crank the car the pedal just goes all the way to the end if i apply the brakes.

xpernet
_________________
1977 Porsche 924
Sunroof Delete
Megasquirt II EFI & EDIS
Carrera GTS / 944 Body

"If one does not fail at times, then one has not challenged himself." Ferdinand Porsche

[Smoothie]

The lower blue part at bottom-right of this pic is the brake booster check valve. The fat vacuum line to it is the one to disconnect and block for testing. The check valve should allow flow only in the from-booster-to-manifold direction (right to left in the picture) -
http://pg.photos.yahoo.com/ph/smoothies931pics/detail?.dir=bdb3&.dnm=9e98.jpg&.src=ph

The brake boosters' function in life is to make it easier to operate the brakes - the pedal should move down further and easier when there's vacuum in the booster (engine running). As long as the brakes are operating correctly, it's normal for the pedal to move further when running. If it goes all the way to the floor with no braking occuring, you have a different brake problem - such as air in the lines and/or bad mc and/or slave cylinder/s. If the pedal feels the same whether running or not, then there's a problem with the booster, the vacuum supply to it or the check valve. Apparently, your booster is functioning at least well enough to operate the brakes, but there's still the possibility of a vacuum leak, so pull and block the hose as mentioned before and check the check valve. -And check any other vacuum check valves that you find. That's another one in the pic appearing higher up to the right - you may or may not have one there, but they're all similar in appearance and should all flow toward the manifold.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[CMXXXI]

The brake booster is that big black round thing that the master cylinder and brake fluid reservoir are attached to...
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'79 Eurospec 931