Fuel Pump Upgrade

[Alpha D]

Question so what happens to fuel pressure regulators that rise at the 1:1 rate. Do they rise and then drop back to the set pressure once you go into vacuum? Or is fuel bled of through the return line to maintain the set pressure?

[mlomker]

It does that would mean. . .for the guys at 30psi plus there FP goes up to upwards up 70PSI?

Right. My car typically idles at 43-44psi and I'm running 25psi of boost so it goes to 68-69 under boost.

The number to be concerned about when it comes to fuel pumps is whether it can deliver the lph/gph at full boost that the motor needs. If a fuel pump doesn't have enough flow at that psi then the psi will drop.

It was exactly that issue that I spent a lot of time troubleshooting this year...looks like it may have been a new fuel pump that was defective. That was the last thing I suspected, of course. lol.

[mlomker]

Question so what happens to fuel pressure regulators that rise at the 1:1 rate. Do they rise and then drop back to the set pressure once you go into vacuum? Or is fuel bled of through the return line to maintain the set pressure?

You normally set the regulator without the vacuum line attached. As an example, my car idles at 44psi or so but it'll drop to 40 under vacuum.

[Alpha D]

Thats crazy 70psi of fuel pressure man. So what happens when your fuel pressure drops under WOT stumbling hesitating ect? mlomker that explain your little quote under your name ha!

[MATCHBX]

It does that would mean. . .for the guys at 30psi plus there FP goes up to upwards up 70PSI? That is serious pressure. . .technically according to his analogy that still wouldn't be enough to render the pump useless since even under hard acceleration the pump only uses 1/3 of its capability meaning at 40-47psi random honda spec. . .120PSI would be needed to max out the pump. Thats just ridicules i dont care what he says 120psi to max a stock pump that dosnt even make any sense.

Efficiencies of the pump change for each amount of pressure it sees. The efficiency is not constant across the pressure range. It may start out at 95% efficient at 5psi FP, but drop to as much as 45% efficient at 70+psi FP. The resulting graph of efficiency % would be a declining line rather than a straight line. That loss in efficiency percentage has to be taken into account.

The reason the FP is a 1:1 rate or rise with boost is the fact that the vacuum line is acting on the same side of the diaphram as the adjustment spring. So basically under vacuum condition (idle), the only force acting on the diaphram is the spring rate (say set to 40psi for round numbers). Once you start adding pressure (boost) in that vacuum line, then the diaphram is being acting upon by both the spring rate AND the pressure in the line. So they are additive. 40psi setting + 20psi boost = 60psi FP. Pretty simple really.

[Shane@DBPerformance]

Most pumps have a crack/bypass pressure and above that the amount of fuel flow drops like a rock.

[mlomker]

So what happens when your fuel pressure drops under WOT stumbling hesitating ect? mlomker that explain your little quote under your name ha!

It'll go lean and the motor will stumble hard.

Yeah, I've struggled with one fuel-related issue after another since my car was built. I'm hoping it's resolved but I won't know for sure until I have the funds for a tuning session.

[Murlo26]

It'll go lean and the motor will stumble hard.

Yeah, I've struggled with one fuel-related issue after another since my car was built. I'm hoping it's resolved but I won't know for sure until I have the funds for a tuning session.

Sell a set of injectors, problem solved.

[mlomker]

Sell a set of injectors, problem solved.

I have a hard time selling $900 injectors for half price or less...and that's all that anyone wants to pay for used parts.

[Murlo26]

Shit for half price I'd almost consider buying those, lol :)

You need to try harder, sell them locally, someone will buy them.

Enough OT from, lol.