79 3.0l fuel pressure

[DeFreest]

I have a 79 911 SC stock and I think I have low fuel pressure but not sure. The engine doesn't run on all 6 and I know I'm getting spark. I think some of the injectors don't have enough pressure to open. I hooked up the pressure gages to the WUR and have a 43 psi system pressure. I have searched the forums but I cant find the pressure value for the 79 system.
So my questions are am I hooking up the gages in the right place? and what should the pressures be?
I am going to replace the fuel filter just in case it's plugged. And lastly what manual is good to own for this car?
I have a Haynes manual that covers a broad range of years that make it difficult to find the right specs for my car and I don't like its lack of information when you do find the right section.
So where can I find the correct or at least better more informative manual for the 79 SC?

[ossiblue]

Originally Posted by DeFreest

I have a 79 911 SC stock and I think I have low fuel pressure but not sure. The engine doesn't run on all 6 and I know I'm getting spark. I think some of the injectors don't have enough pressure to open. I hooked up the pressure gages to the WUR and have a 43 psi system pressure. I have searched the forums but I cant find the pressure value for the 79 system.
So my questions are am I hooking up the gages in the right place? and what should the pressures be?
I am going to replace the fuel filter just in case it's plugged. And lastly what manual is good to own for this car?
I have a Haynes manual that covers a broad range of years that make it difficult to find the right specs for my car and I don't like its lack of information when you do find the right section.
So where can I find the correct or at least better more informative manual for the 79 SC?

The Bentley Manual is the "bible" for SC and later 911's and is a must-have for DIY.

Hook up your fuel gauge in the following manner: Disconnect the fuel line from the fuel distributor to the wur, at the wur. Connect you fuel gauge to the wur with the shut-off valve on the wur side of the gauge and the line from the fuel distributor is connected to the hose on the gauge that goes directly to the gauge.

Once connected as above, close the valve and start your fuel pump by either jumping the terminals at the fuel pump relay (terminal 30 to 87a) or unplugging the wire to the air flow sensor, and turning on the ignition switch. The reading you get will be the system pressure which should be ~75 psi or greater.

If you recorded the correct system pressure in your post (43 psi) then you do have an issue. If your pressure reading was cold control pressure--valve was open and gauge connected correctly, then you are within range of proper pressure, depending on ambient temperature.

Basically, double check your gauge set up, report to us you system pressure and cold control pressure, and report back. We will need this information to proceed without just guessing.

[timmy2]

Get the Bently manual first and read it. It will become clear how and what to test.
Download the workshop manual as well. Cannell uk has it, google it.

[DeFreest]

Originally Posted by ossiblue

The Bentley Manual is the "bible" for SC and later 911's and is a must-have for DIY.

Hook up your fuel Gage in the following manner: Disconnect the fuel line from the fuel distributor to the wur, at the wur. Connect you fuel Gage to the wur with the shut-off valve on the wur side of the Gage and the line from the fuel distributor is connected to the hose on the Gage that goes directly to the Gage.

Once connected as above, close the valve and start your fuel pump by either jumping the terminals at the fuel pump relay (terminal 30 to 87a) or unplugging the wire to the air flow sensor, and turning on the ignition switch. The reading you get will be the system pressure which should be ~75 psi or greater.

If you recorded the correct system pressure in your post (43 psi) then you do have an issue. If your pressure reading was cold control pressure--valve was open and Gage connected correctly, then you are within range of proper pressure, depending on ambient temperature.

Basically, double check your Gage set up, report to us you system pressure and cold control pressure, and report back. We will need this information to proceed without just guessing.

Ok Thanks. I hooked up and have a system pressure of 5.1 bar and cold pressure of 3 bar at 78 F. Checked the injectors and there working fine. Guess it's spark after all. Plug wires look old so will do a tune up. Wires cap rotor and plugs and report back. Also will change out the fuel filter for good measure.

[DeFreest]

Originally Posted by timmy2

Get the Bently manual first and read it. It will become clear how and what to test.
Download the workshop manual as well. Cannell uk has it, google it.

Fantastic. Thanks.