polskifacet said:
What will having a higher performance fuel pump accomplish:
Having a larger fuel pump could "mask" the issue etc but if its allowing the car to keep full fuel pressure then case closed?
Larger HPFP can't suck more fuel out of the tank per se, if its a feed issue, I should have the same issue with a big pump?
Is LMS able to generate more power on stock turbos with the bigger pump? If so I would experience the same issue when getting closer to the limit of the pump if it was a ecu/signal issue?
So what I have read it sounds like all of your individual physical parts have been tested and pass testing. If the pumps test fine and they tested that they can sustain flow AND pressure properly, That tells me your problem lays outside of the individual components and is in the system itself.
This may not be what you want to hear, but I think everyone here is genuinely just trying to help you out.
This is something I have had in my head the last week or two following along in this thread and been waiting to say pending the testing you were doing.
I think it would be interesting to see what the fuel pressure is coming out of the tank right at the tank and right before the HPFP, then also at the HPFP outlet and all the way at the last possible point at the rail. No idea how you would hook sensors up and monitor them during run/passes. Any notable drop between the pairs will tell you that you have a clog someplace between the gauges and could very easily explain your car not recovering FP easily when tuned. Your car may be just fine under low demand like when it is stock (this is a long thread, have you run a log with bone stock tune?), but once you exceed a certain demand (custom tune) then the car is asking for more fuel than can be supplied past the restriction. I work in hydraulics and this is troubleshooting 101 dealing with pressure/flow issues in a system. You look for the pressure drop, we see it all the time in mobile machines were something has caused a restriction in a line. Could be a kink, piece of debris, bad connector, you name it. A kink for example may restrict the flow of your fuel line 25%. Not an issue in stock trim as the car at WOT may only need 70% of max line flow. But with tune, you may need 90% of max fuel line flow to stay at pressure, but your line is only able to flow a max of 75% so you are short 15%. Static pressure test, all will look just fine, you have to check under max flow demand as well.
Having a larger (stronger) pump may mask your issue and get you off and running. But you would then again have issues trying to use the pump to its actual HP capacity at a later time. While I can appreciate that it is a "fix", it is just not the right way to fix an issue like you are having. It is like if someone had installed ballast in your car before you got it. You get it and try 1/4mile and it is running high 14 second, when everything on paper says it should be mid 13's. You could just throw more HP at it with a tune and get yourself back to where it should have been stock, or look around and realize that it has extra weight and get it removed. Then when you do the tune you are right with everyone else rather than having spent extra $ to be where everyone else started from... You will also be working that stronger pump harder all the time, as it will be pushing higher pressure to overcome that flow restriction.
If your current HPFP is being starved then it would not be able to keep pressure. There could be a restriction between the low pressure intank pump and the high pressure. That is what I am thinking at least, and gauges as mentioned would show that. If the pump in the tank is putting out say 80psi at idle, but the inlet of the high pressure only sees 60, then you have an issue. If that differential gets bigger as you rev the engine, again, it points to an issue, the high pressure is asking for more than the low pressure can feed it whether because the low pres pump is bad or the line restricted..
