Monday morning. I started the car. It started easily and warmed up well, but as the temp gauge hit 80, the idle went rough, and the engine died. Again, a very difficult re-start. Fuel-related, I thought, so I did a fuel volume check just aft of the regulator/dampener. It pumped a pathetic tenth of a liter in 30 seconds. Fuel filter in the engine compartment was clean. Fuel tank and pump appeared new, with correct hoses and clamps. Took out the fuel sender and found a perfectly clean tank, screen, and flower pot. Noted that the plumbing had the "Y" that diverts some of the returned fuel to the bottom of the pump, again with all new hoses and clamps.
Took the fuel cap off, and the car started instantly. Thinking I was on the trail, I checked the vent lines and the canister in the trunk. All good. A red herring, starting deteriorated even with the cap loose or off. Frustrated, I quit for the day.
Tuesday morning. With the engine cold, did another fuel volume check. This time I got the full liter in 30 seconds. I thought this was interesting enough to consult an expert, who told me that what i was seeing was not possible. How could fuel delivery change with temperature? Left to my own devices, I sucked it up and checked the small filter in the pump, which was clean. I unhooked the supply line from the pump and blew it out from the engine compartment back and also disconnected and blew out the S-hose from the filter to the pump. No obvious blockages in either.
Running out of options, I decided I might as well blow out the return line as well. To my surprise, it initially resisted the air pressure, then gave way, and the tank made gurgling noises. Well, that's something, I thought, so I reconnected everything, started the engine and warmed it up. The first hot start was excellent. Others, at intervals of 15, 30, 60, and 120 minutes were also good. The problem appeared to be resolved.
I drove the car for a couple of days, no hot start problems. In fact, starting was best leaving the pedal at rest. Previously, the car had always needed half or full pedal for a hot start.
But why did clearing the return line fix a supply problem?
I think Joe Alexander nailed it in a recent thread on hard hot starting:
"This continuous volume of fuel cools the IP and the fuel itself as it circulates. If the fuel volume or pressure is low, the fuel system will become leaner. and hotter. Fuel can actually boil or vapor lock in the IP or the injector lines in severe cases. Good fuel volume and pressure during start up, helps clear the lines and cool the fuel system. This is why a plugged fuel return line can cause severe starting problems, since the fuel cannot circulate or cool the system."
What this experience adds, I think, is that problems with the fuel return can also affect fuel delivery volume.
The unsolved mystery, is what caused the return line to become plugged?
