odonnell

You have a check valve installed that works, and the injectors aren't leaking

If you are losing pressure, at least one of the above can't be true anymore, unless it's going into your vacuum line (sniff FPR vac line?)

If the check valve is working, then the system would hold pressure for a lot longer regardless of the FPRs design. and likewise, if the check valve IS working as intended, then your injectors are leaking. There's simply nowhere else for the fuel to go besides the FPR vacuum hose.

nick_968

I am not sure you are correct. The check valve is on the flow side, the FPR is on the return line. If the FPR is losing pressure (which it does by design) then that is where the pressure goes, down the return line. The vacuum line is dry, that would be an easy one if it was wet as you just replace the diaphragm in the FPR. Fuelab themself advise that you will lose pressure after them pump is shut down, it does not work like a factory regulator.

Tom M'Guinn

To test the pressure theory, you might try leaving the pump running after you shut off the motor (to keep the fuel circulating and cooler) and see if you still have the hot start issue.

nick_968

I am past that point now, all the lines and the regulator are off waiting for the new parts to go on once they arrive this week. I could hot start it if I restarted within a minute though, much longer than that and it got progressively harder to start as the pressure dropped off further. Who knows if this is the problem but by trying the factory regulator I can eliminate one more link in the chain. I have replaced pretty much everything else.

Jay Wellwood

later model 928s have experienced the same issue. IRRC, replacement of the check valve and the damper seemed to be the cure.

Might do a quick search there.

nick_968

The check valve is new. The Damper is Marren and although not new, is not old. No visual signs of leaking but that will be the only item I have yet to replace on the fuel system. The good thing is I can screw my pressure gauge into the FPR adapter that I have ordered so I will be able to see straight away if the pressure drops off after shutdown. If it does then I know there is something else in the system failing.

notny41

Did you get this fixed? If so - what was the culprit?

nick_968

Turned out everything in the fuel system was fine, there is a natural decay of fuel pressure in the system, certainly on mine (which is far from standard). The problem was a setting hidden in the Motel software menu which effectively sets the filtering of the crank signal to a percentage to determine what is an error and what is normal noise. Mine was set to a value that was too low and this meant that on cold starting there was no error, but on hot starting it was giving a slightly more distorted signal which resulted in no spark being given intermittently. Three Motec specialists failed to pick this up over the years. I only solved it in the end after learning to map the car myself and working through every setting in the system having eliminated anything physical under the bonnet. In the end it was a Motec webinar that alerted me to this setting when I was learning about potential causes of ref and sync errors and how to perfect the setup. The issue was with me for so long I still think the car is going to struggle to fire up after stopping to fuel up or similar. A very nice feeling when it starts on the button