1979 911SC CIS trouble

fredmeister · fredmeister's Garage

I have a problem with both cold start and warm start on my 1979 911SC with CIS injection that I could use a hand solving. Here is a description of what is happening and the results of system pressure readings I took th eother day:
Upon trying to start the car after sitting overnight....(COLD START) the car will fire momentarily for a half second and then immediately quit. After trying to start it this way for 4-5 times it will finally run at high idle 2000 rpm and gradually settle at 1000 rpm after 30 seconds or so as it warms up.
It will idle this way normally for however long I let it run, however, if I shut it off and IMMMEDIATELY TRY TO RESTART (WARM START) IT IT WILL NOT EVEN KICK.

Now I hooked up CIS pressure gages and got the follwoing readings:
Cold pressure= 2.3bar
Warm pressure= 3.2bar
Control pressure (cold, engine off)= 2.8bar
Rest pressure after shut down= 1.8bar
Rest pressure after shut down (20 minutes later)= 1.4bar

NOW HERE ARE MY QUESTIONS:
1) ARE THESE PRESSURES NORMAL OR OK?
2) With the gages I was able to shut the flow valve in the line between the warm up regulator and the fuel distributor when it was running and I SAW NO CHANGE IN THE PRESSURE OF 3.2BAR WHEN I OPENED AND CLOSED THE VALVE, IS THIS NORMAL?
3) WHAT WOULD CAUSE THIS COLD AND HARD STARTING PROBLEM?

Any input is really appreciated as this hass got me at wits end.

Fred

cmonref · 07-31-2007, 06:16 PM

Your pressures are about right. The COLD pressure of 2.3 bar is correct at about 70-84 degrees F ambient. The HOT pressure is about right: spec is 2.7-3.1 bar without vacuum to the WUR, and 3.2-3.6 bar with 450-550 mbar vacuum on the WUR.

Rest pressures after shutdown show that the accumulator and fuel pump check valve are OK.

Don't think pressures are causing your problem.

A bad, or failing, fuel pump relay might cause what you are experiencing. You DO have a spare, don't you? A spare is highly recommended, because the relay IS different (more than just being RED in color) and you won't find one in an autoparts store in Lower Jibbup on Sunday afternoon.