Fuel Pressure Issues

[phocussed]

I have a 1980 911sc. Just finished the ground up restoration and working out some kinks. One of which is the CIS.

The engine is brand new, and running rich, poor cold idle. It reacts to tuning, but I thought it best to check the fuel pressures prior to monkeying with too much.

All possible vacuum leaks were buttoned up during rebuild (I did it.. so I know).

Here are my results:

1. Fuel Pump is about 10 years old. Fuel pump on, test valve closed the system pressure is 69 PSI (4.75 bar)

(suspected that it might have sucked up bad gas from the gas left in tank during restoration.. replaced, same readings)

2. Fuel Pump on, valve open... the same

3. New accumulator, residual pressure is 60 psi.

4. WUR unplugged, FP on, Valve Open, 69psi

5. WUR plugged in, FP on, Valve Open, 69 psi

6. Checked voltage to WUR... about 10.4 volts

7. Checked ohms at WUR... not open, some resistance (sorry, number escapes me)

Before I spend $$$ on a new WUR... any suggestions of the cause of the lack of pressure fluctuation?

Thanks in advance,

Rick

[turborat]

Rick,

Spend some time looking over the engine electrical harness connector and wiring before too much adjusting or replacement of components. You mentioned 10.4 volts on one of the connections. One would expect to see 12 volts with ignition on or a little higher with the engine running.

I had the exact same symptoms on my SC after I removed and replaced the engine. The wire-ends break and corrode where they are secured into the pins that make up the engine harness connector. Separate the harness and carefully remove the covers to get a closer look at each wire and pin.

[ossiblue]

Assuming you have the gauge set hooked up correctly, it appears that you may have a blockage in the WUR. The pressure readings all appear to be around spec for system pressure and the fact they do not drop indicates the fuel is not flowing freely through the loop of the WUR.

You might try removing the return line from the WUR, placing it in a container, and test again to see if fuel is actually flowing through. (Do this carefully, with a fire extinguisher handy.) There is a screen in the entry port of the WUR that could be clogged and you might check that also.

If fuel is flowing, have you tried adjusting the cold pressure on the WUR by knocking down the pin? If not, try that and if you succeed in dropping the pressure, you can then move on to adjust the WUR once you determine the heating element is working.

The pressures you record would lead to a lean condition rather than an overly rich one as you describe so how you determined the overly rich mixture is important. If it is truly too rich, once the pressure issue is settled you will need to adjust the fuel mixture screw in the FD.

[phocussed]

I believe it is running rich because the rings are not seated yet.

I took out the wur this morning and there was some crud in there. I've disassembled up to the thin metal disk, I'll tackle that tonight... I didn't want to risk rushing and damaging it. I hope to find a blockage, but the screen was pretty clean.

The system did sit for 2 years while the car was restored... so it is possible there is a varnish build up.

I will also check on the electrical connections throughout.

Thanks so much for your prompt replies.

[boyt911sc]

Phoccused,

LJ has given you the right direction. Unplug WUR the return line and let the FP run a few seconds with the pressure gauge attached. Check for the drop in control pressure. Two (2) things come to mind: micro mesh @ WUR and primary pressure return valve. Keep us posted.

Tony

[phocussed]

Well... one problem solved, one remaining.

The reason the pressure would not drop is that the gauge was defective! I exchanged it this morning and voila.... I have readings. Oh the joys of Chinese tools.

Ok... here are my readings.

System Pressure: 70lb (4.8 bar)
Cold Control Pressure: 58psi (4 bar)
Warm Control Pressure: 69 psi (~4 bar)
Residual Pressure: 25lbs. (1.6 bar) after 20 minutes

So it appears that my cold and warm pressure is too high. Is that something I can adjust in WUR myself, or is a rebuild in order? I took the thing apart and cleaned it, so I am not intimidated by the guts.

[phocussed]

New update!!!!!!

Found the problems:

1. Faulty Gauge replaced
2. Bad O ring in pressure regulator on fuel distributor

New Numbers:
System: 60 PSI, 4.2bar
Cold Control: 27psi (1.8bar)
Warm Control: 50psi (3.5 bar)

I know the numbers are a little off, I am going to start by ordering a shim or two to bump up system pressure and see were we are then.

Thanks so much for all your input! Patience, patience, patience..