944S, difficult start when hot
10-19-2017, 01:53 PM
#1
944S, difficult start when hot
This problem has persisted for many years (according to the previous owner) and generally appears after about 10 mins after a shutdown when hot. If I go to start before the 10 mins., it usually starts without issue. Otherwise I usually have to press the accelerator when cranking and it will catch after 5 seconds or so.
What seems to help is if I rev to about 3 or 4k rpm when shutting it off (switch key to off when engine is still revving high). This method seems to help 75% of the time.
Do the above symptoms point to anything concrete?
What seems to help is if I rev to about 3 or 4k rpm when shutting it off (switch key to off when engine is still revving high). This method seems to help 75% of the time.
Do the above symptoms point to anything concrete?
10-19-2017, 02:58 PM
#2
Burning Brakes
It sounds like vapor lock.
You need to check the fuel pressure after turning the engine off. The fuel pressure is held by a one way valve on the fuel pump. A leaking injector or fuel pressure regulator can also cause the pressure to drop.
To check the fuel pressure it gets a little complicated since the fuel rail fitting is an oddball type. You could fabricate one out of the right size hose and clamp a gauge to the nipple, or buy a fuel pressure gauge from Arnnworx that has the right size fitting:
http://www.arnnworx.com/catalog/inde...9#.WejmkFuPKUk
The fuel pressure should remain above half its operating pressure for about 20 minutes. This is not exact but there is more information in the Porsche service manual.
It is usually pretty obvious, when you turn off the engine, the fuel pressure should stay high; if it falls rapidly then there is the problem.
Please have a fire extinguisher and a water hose with pressure handy when you work on the fuel system. No paranoia, just good common sense. In fact, it's good to have a fire extinguisher close by anytime you work on a car. You will probably never need it, but...............
You need to check the fuel pressure after turning the engine off. The fuel pressure is held by a one way valve on the fuel pump. A leaking injector or fuel pressure regulator can also cause the pressure to drop.
To check the fuel pressure it gets a little complicated since the fuel rail fitting is an oddball type. You could fabricate one out of the right size hose and clamp a gauge to the nipple, or buy a fuel pressure gauge from Arnnworx that has the right size fitting:
http://www.arnnworx.com/catalog/inde...9#.WejmkFuPKUk
The fuel pressure should remain above half its operating pressure for about 20 minutes. This is not exact but there is more information in the Porsche service manual.
It is usually pretty obvious, when you turn off the engine, the fuel pressure should stay high; if it falls rapidly then there is the problem.
Please have a fire extinguisher and a water hose with pressure handy when you work on the fuel system. No paranoia, just good common sense. In fact, it's good to have a fire extinguisher close by anytime you work on a car. You will probably never need it, but...............