911 SC Fuel Pressure Diagnosis
We are having a very brief cold start problem in this 911SC. After the car sits for about 8 hours, it struggles to start for a few seconds. Once it has started once, it will start immediately for the next 6-7 hours like everything is normal. Once it sits overnight, it struggles again. This makes diagnosing the issue very difficult, as you can’t tweak something, check it, tweak something else, check it. Instead you get one shot, then have to wait 8 hours for it to act up again. And repeat the process.
There are a couple things that can cause this, including the cold start valve, thermo-time switch, and the warm up regulator (WUR). On any CIS system, knowing what your system pressure, control pressures (hot and cold), and residual pressure, are critical to diagnosis. These are all tested by attaching your fuel pressure tester between the WUR and the fuel head, and using a jumper switch on the fuel pump to check the individual pressures.
Our pressures all checked out within spec, which is good, this means our fuel system should be good. On to the thermo time switch and the cold start valve testing.