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carrera 4 poor starting when left


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hi all

i have a porsche 996 carrera 4 2002 model year manual gearbox

it has a fault the longer its left the longer it cranks over before starting.

checked on pst2 no faults found . when a fuel pressure test is done its showing 7 bar at idle and no residual pressure when switched off ? it also takes about 10 seconds of continual cranking to build the pressure up when cold. can anyone confirm the spec for pressure and residual pressure on this model

many thanks simon

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I don't have the exact pressure schedule in front of me, but 7 bar (= 7Kg/cm²) at idle is more than (in general, for most of Bosch systems) needed, i doubt if the engine will run under this conditions. I would check the quantity (amount) of fuel flow first, partial clogged fuel filter, partial clogged or clamped fuel lines (inclusive return line, fuel pressure is controlled by the variable opening and closing of the return line by the fuel pressure regulator(s), can cause that phenomenon. A worn fuel pump act a little different, but i would check that out as well.

Just found the values for 997 which are approx. the same and may used as a benchmark value: 3.8 bar +/- 0.1 with a flow quantity of 80 liter/h.

Hope it helps.

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thanks for your replys .

i have found that on model year 2002 the fuel system was changed from a return line system to a non return line system. this car looks like its been messed about with ! found a bolt jubilee clamped into a cut off fuel line :eek: but cant see the other end of line . the vin no is wpozzz99z2s608829 can anyone confirm which type or fuel line system this car should have ?

thanks very much simon

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thanks for your replys .

i have found that on model year 2002 the fuel system was changed from a return line system to a non return line system. this car looks like its been messed about with ! found a bolt jubilee clamped into a cut off fuel line :eek: but cant see the other end of line . the vin no is wpozzz99z2s608829 can anyone confirm which type or fuel line system this car should have ?

thanks very much simon

That VIN checks out as a MY2002 - so it would have the returnless system.

You can read about the system in the Porsche Tech Book here (for Contributing Members only)

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Return less system means that there is no longer a return line from the engine to the tank, in this case the pressure regulator, short return line (calibrated hole), fuel filter are all part of the fuel pump unit inside the tank. Bosch systems use the return as supply pressure, the more the fuel return get squeezed, the higher the supply pressure will be. I hope this is a little clearer.

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