Is there a fuel "one way" valve ?

[Paul99]

When I first start my 230, I have found waiting with the ignition on for 30 secs or so before starting, it seems to start far easier.  It could be the fuel pump is a bit tired, or a red herring re easier starting.  Car runs perfectly fuel wise once started.

I was thinking, is there a "one way" valve which would stop the fuel falling back, so the fuel line is always primed? Or is it normal for the pump to need a few seconds to get the fuel fully delivered?

[mdsalemi]

Paul,

What you experience is completely, 100% normal.

When you turn on the ignition, the fuel pump at the rear of the car by the fuel tank begins to pump, and circulates the fuel in a loop from the pump, through the lines, to the fuel injection pump in the engine compartment, and back to the fuel tank. Leaving the pump on for a few moments prior to engaging the starter allows this system to build pressure and volume flow.

I don't think you need to re-engineer the system. 

[garymand]

There may well be a one-way valve effect in the dampener/regulator on the later motors.  The diaphram works against a spring that sets up a back presssure.  And I think you are thinking down the right path.  If you have a leak, as maybe in the cold start valve solenoid, the back pressure is lost and it might take a few more turns of the pump to fully pressurize the fuel lines. 

I have notice occasionally when I let the car rest for a few weeks, it takes a little longer for the pump to reach full pressure.  It is maybe 2 seconds where you can hear the frequency of the pump whine change as the pump brings the pressure up.  It could also be the pump is overcoming stiction/friction after sitting for weeks.

When mine is daily driven, I don't hear the pump free wheeling with no back pressure at starts.  And usually, I can go for maybe a week or more before noticing change in pitch.  I'm also saying I have noticed it and now wait often to hear the pump and get that satisfying feeling that it should ignite instantainiously.

When I have had some delay in ignition, it has been due to my misadjustment of the idle or warm up device.  When the system is setup correctly, its a joy to have the motor start like a new car.  Conversely, when something isn't right, it is a really downer to have it turn and turn with ought starting.   

[Jordan]

Paul, I believe there is a valve in the fuel pump itself (the one at the back) that prevents the fuel from flowing back into the tank when the pump is not running.

[wwheeler]

Correct me if I am wrong, but I believe that the valve fitting towards the rear of the pump acts more as a restrictor and is responsible for building pressure on the supply line. Could also act as a check valve.

[Paul99]

OK, many thanks guys.  I do only use the car every week or so, so the 20 secs or so  delay with the pump running before starting seems a good idea, and is no hardship.

its been a great summer here and had some great drives in the car including LeMans Classic weekend where I had a chance to drive the circuit just before the race started!  Its a lovely elegant car to drive as you guys know !  I was lucky to be able to buy it some 3 years ago before the prices went mad and out of my reach.  Hope to keep it until I cant manage to get in or out of it without a hoist!

[Shvegel]

Check valve at the outlet of the fuel pump and each of the 6 delivery valves under the outlet fittings of the injection pump. Combined with the fuel injectors holding pressure at rest and the delivery valves acting as a check valve on the inlet the individual lines should each remain under pressure at rest.