Porsche Enthusiasts Club Forum

good evening chaps, i have an early 944 with a 968 engine and it has started having hot start problems.
unfortunately i am moving abroad tomorrow and don't have time to book it in anywhere.
So i will pack a box of tools and have to deal with it when i get to france.
I am taking an as new crank sensor incase it is this, and will check the vac lines when i get there.
Can anyone suggest any other possible causes?
TIA, Mitch.......

Retained fuel pressure is my suggestion.

do you mean it over fuels on restart?

No, I mean that it doesn't retain fuel pressure after shutdown as it should, which can make restarting when hot difficult.

thanks will look into that too

im curious as to why this would only affect a hot start, it starts perfectly when cold but tries to stall if i don't give a bit of throttle when hot starting and the idle lopes a bit.

Because the boiling point of fuel is lower than the temperature of a running engine. But as you pressurise it, the boiling point goes up, eventually above 2.0 bar the boiling point of fuel ends up above the temperature of a running engine.

Once you shut down the engine, the fuel warms up to the engine temperature, the engine cools and so does the fuel again.

Also once you shut down, the fuel pressure decreases as some of the fuel weeps back into the tank past the fuel pump check valve.

So, if the rate at which the pressure, and therefore the boiling point of the fuel, decreases, equals the temperature of the cooling engine, the fuel boils, turns to vapour and when you try to start it, it can not pump fresh fuel in to replace the vaporised fuel and causes a hot start problem.

Usual cause is a fuel pump check valve allowing the fuel to go back to the fuel tank too quickly once the fuel pump shuts down... otherwise it can be a dribbling injector or a weeping fuel pressure regulator.

thanks for the info jon, firstly how was the track day??
and secondly is this hot start something that requires attention soon or could i live with it for the summer?? it wont idle on hot restart without a bit of throttle and the idle lopes a bit with a very slight misfire i think.
i have found a main dealer in Nantes i could approach if necessary for parts/service. cheers. Monsieur Mitch....