new fuel pump, runs like a scalded dog

[fast97gt]

alrite here it goes, i was riding down the road and it happened she died. i feard the worst, cause i just got done puttin her throught the paces. i had it towed home were i found to my releif, it was the fuel pump. so i ordered and installed a jegs 255lph fuel pump. now i know for a fact this is not an infigmant of my imagination, but the car pulls like hell, i thought it ran good after the pi engine swap but fellas this things great now. the question is why? can anyone explain. ps the engine swap has been done for a year now so theres not anyway the pump could have been going "bad".

 

[trinity_gt]

The only logical conclusion is the engine was previously starved for fuel.

Without some sort of objective, empirical indication (e.g. an AFR meter and/or a fuel pressure gauge at the rails) we can only assume that better performance after a fuel pump ---> fuel starvation before the fuel pump.

 

[fast97gt]

this is true, but my thoughts were that witht the stock pump fuel delivery at a higher rpm is limited because of the pressure drop and with the pump set at around 70-80% duty cycle the pressure is there but the volume isnt?(correct me if im wrong please) but now with the higher flow pump, wouldnt that be like tuning the factory pump to a 100% duty cyle thus delivery more fuel at the same pressure?

 

[fast97gt]

also would an adjustible fuel pressure regulator be worth gettin to better tune it?

 

[trinity_gt]

this is true, but my thoughts were that witht the stock pump fuel delivery at a higher rpm is limited because of the pressure drop and with the pump set at around 70-80% duty cycle the pressure is there but the volume isnt?(correct me if im wrong please) but now with the higher flow pump, wouldnt that be like tuning the factory pump to a 100% duty cyle thus delivery more fuel at the same pressure?

I'm not as familiar with the fuel pump control in the return-systems but I believe the pump is simply driven by the fuel pump relay at "100%". The FPR and return lines maintain the correct pressure at the rails.

If the fuel pump lacks the volume to supply the engine the pressure at the rails will drop and that would be seen on a gauge. Since the pressure is "set" by the FPR then, at this point, the FPR would be commanding maximum rail flow (minimum return flow) and the pump itself becomes the limiting term.

also would an adjustible fuel pressure regulator be worth gettin to better tune it?

It's possible. Ideally you want ~40psi across the injectors. That's what the PCM expects for its fuel calculations. If for some reason your current setup is, say, high (for example, the volume available from the pump overwhelms the FPR and return lines to some degree producing a pressure higher than required) it may be worthwhile looking at both the FPR and the up-sizing the return lines.