Hi recently having a cold start missfire and stall, swapped out the high pressure fuel pump, new plugs, coils etc. appears to be fuel related. no issues after car driven for 1 minute. I suspect a leak down of fuel pressure in the low pressure supply side. Does anyone knows if there is a separate valve that prevents back flow or is it built into the transfer pump in the tank. I used to work for w Mercedes Benz and they had an issue with the B class fuel pumps leaking down overnight causing a cold start issue. possibly the same issue here? anyone else had this problem??

 

Well...... I honestly have no idea. One of the other guys who are more schooled on the fuel side of things will have to weigh in on that. There is a second low pressure pump. That should provide some pressure when the key is on. I think it’s around 60psi, but don’t quote me on that, is been a while since I’ve looked into it. But with everything you’ve replaced, it would seem a logical next thing to look at. Along with the injectors and fuel rail seals. Do you have a scan tool or something that you can use to monitor the fuel pressure on a cold start?
Or you may have gotten a bunk HPFP?

 

strange no missfires or codes when hot, RPM tune running 20 psi boost, you would think if there was a injector seal or fuel rail seal leaking it would cause an issue under high load/high rpm. might have to swap out the fuel tank transfer pump next