warm start issue 911 3.0 sc

[mirat]

hi

the car won't start when it's hot..the car is 911 from 1968 with engine 3.0 sc from 1980

new parts:
fuel filter
fuel pump
fuel accumulator
injectors
WUR is testet 1.5 bar (cold) 3.6 bar (Hot)

it's a clean engine without lambda and control box, when i check the fuel pressure(cold) it goes to 1.5 bar and within minutes then goes to 3.5-3.6 bar, but when i take the ignition off (fuel pump) the pressure drops to 0 bar right away.

what is keeping the pressure in the system? when the pump is off, i can understand that it's a combination of the pump and the accumulator, but what about the return fuel line, should there be some kind of valve to stop the return and hold pressure.
i am a bit confused about this.

BTW. engine starts fine when it's cold

Br
Michael

[proporsche]

Hi ..yes there is a fuel pump check valve...like this one..that could be your culprit.
Ivan

[boyt911sc]

Michael,

Test your residual fuel pressure. Your pump might not have the check valve used in later CIS cars or the check valve is leaking. Test and inspect your FP.

Tony

[ixxified]

Originally Posted by proporsche

Hi ..yes there is a fuel pump check valve...like this one..that could be your culprit.
Ivan

In what way?

[timmy2]

Residual pressure is on supply side. None on return side.

[boyt911sc]

Originally Posted by ixxified

In what way?

The FP check valve prevents the return flow of the fuel to the gas tank after the FP ceased running. Thus preventing the sudden loss of residual fuel pressure in the system. There are several known culprits to cause residual pressure loss and the FP check valve is one of them.

Tony

[mirat]

hi

yes yes...found the problem, there were no valve in the in the fuel pump on the pressure side, i will install one and check/test again.

Thanks to all for quick response and help to solve the problem, i will write back when i have tested it.

Br
Michael