johnb

1984 euro s 4.7l 16v (no cats) auto, wheel at each corner etc etc.

what is the function of the fuel non return valve?
does it affect the running of the vehicle?

i guess it has a purpose, but if the pump is running and the pressure regs and damper are doing their stuff.....what is the non return valve for?

johnb

Bryan

Uh, non-return valve? Do you mean the check valve in the fuel pump? It's so the fuel lines and rails stay full of fuel. This lets them come up to pressure in less than a second so the car will start immediately. Otherwise, you have to wait for the fuel pump to send fuel all the way up the lines, into the rail, then pressurize it. When I had my 944 apart, it took at least 30 seconds for this to happen when I restarted it (I emptied out the fuel lines when I had the engine apart). I don't want to have to crank the car for 30+ seconds every time I start it.

The check valve is in the fuel pump. Do you have something else in your fuel system in the engine bay besides two regs and a damper? If so, I don't think it's supposed to be there.

Bryan

WallyP

A tight system should hold fuel pressure for a minimum of thirty minutes, and several hours is better. The fuel pump check valve (replaceable separately) is critical to this.

If the fuel pressure is held, the engine will start almost instantly. After the pressure bleeds down, it takes longer for the engine to start. If the system is allowed to drain, starting is very difficult.

dr bob

Reinforcing Wally's discusson, another big reason is to eliminate vapor lock in the system when the pump is shut down. If the pressure is allowed to bleed down when the pump stops, heat in the engine bay will evaporate/vaporize the liquid fuel in the rails and injectors. On warm restart, all that vapor needs to passed through the nozzles or the fuel pressure regulator before liquid fuel is available at the injection nozzle again.

johnb

thanks guys

that all makes perfect sense.

the valve had stuck open in my car. resulting in a small delay in starting....i just thought this was normal. now it has been fixed it starts instantly.

btw: the fix was to clamp off the fuel return line for a second, a couple of times. this shocked the valve back to life. that and plenty of injector cleaner in the fuel. pressure now holds for about 1 hour, slowly dropping to about 30psi over night. before fix, it dropped to nothing instantly.

i love this car, all faults seem to have a logical solution (usually expensive tho'!)oh well, on with fault 873!

regards

johnb <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Normy

John...

You'll find this exotic is exotic in that it is actually easy to work on~

Normy!