Fuel Pressure question

[mb911]

For a cis engine what should the proper fuel pressure be?

Ben
81 SC engine

[Jim Sims]

for 81 SC:

System pressure: 65 to 75 psi

Cold control pressure:
23 psi at 50 degrees F
36 psi at 75 degrees F
50 psi at 100 Degrees F

Warm control pressure: 49 to 55 psi

Rest pressure: 22 psi

Return line fuel flow: 2.2 liters per minute

[mb911]

Thanks that helps. I must ahve a bad WUR as my pressures are way off.

Ben

[Ruben911]

Ben, you don't state what your pressures are. However, I recently used a fuel pressure gauge (bought from JC Whitney) and determined that my WUR had a clogged filter and was not allowing the fuel pressure to drop (control pressure). The system pressure and control pressure were the same (93 psi), which should not be the case. I took the WUR appart and removed the clogged filter and after re-installing it, the control pressure dropped to 50 psi. I recently removed my fuel pressure regulator (back of FD) and removed some spacers and my system pressure is now 75 psi and control pressure is 43 psi. BTW you can check if your WUR filter is cloggged by disconnecting the return line from the WUR (not the line from the top of the FD to the WUR) and running the pump (engine off, cold, and disconnect WUR electrical plug) to see if gas comes out of the return line. If it does not, it means that the WUR filter or the return line itself is clogged. As always, one must be very careful with testing involving gasoline. Hope this helps or let us know what your pressures are so that we can help with the troublesooting. Thanks


Ruben
1976 911 s 2.7L

[mb911]

I was getting about 60 psi cold at about 75 degrees. I am told with higher fuel pressure the car will run lean? That would explain my problem(surging and not much power). I am going to check all the lines for blockage as well. I don't know were the pressure regulator is thow> I thought that was really the WUR.

Ben

[Jim Sims]

See:

Busy Weekend

Jim

[Ruben911]

Ben, what are your system and control pressures? have you measured them. Is the 60 psi you quote control pressure (i.e. without valving off the WUR) or system pressure (with the WUR valved off). The pressure regulator is behind the FD. It is a spring/piston component that allows the system pressure to be increased or decreased by adding or removing thin spacers behind the spring. If you follow the thread that Jim listed, there is a picture of a FD and shows where the pressure regulator is. The pressure regulator is used to adjust the system pressure to specs by adding or removing the thin spacers. My experience with the high control pressure was hesitation under load and a significant power reduction, which was caused by the WUR filter being clogged. If you are going to remove the pressure regulator be careful that you don't drop the cap, washer, spring or piston behind the engine because it will be a nightmare to find. I placed a small towel below the fuel pressure regulator just in case I dropped one of these small pieces while removing them. Hope this helps.

[mb911]

I will check into that. I was testing pressure between the FD and the wur? Don't know if that was correct? Thanks for the help I am going to look into that.
Ben

[mb911]

Ok I've got the pressures all worked out. I bought ben watsons book and it is a great help. Thanks everybody
Ben