EFI fuel pressure ?

[Denvervet]

I am planning on using one of Ricks new efi tanks that is set up for 58psi regulator. Brings up a good question. Why do aftermarket EFI system suggests 42-45psi vs some other pressure? What could or would be the downside of running more or less?
I will be running accel Gen 7 but that's just the ECM . I am not running their regulator or fuel pump, etc.
Is there a difference with how the injectors perform with pressure difference? I can imagine there is but....?

[camcojb]

Originally Posted by Denvervet

I am planning on using one of Ricks new efi tanks that is set up for 58psi regulator. Brings up a good question. Why do aftermarket EFI system suggests 42-45psi vs some other pressure? What could or would be the downside of running more or less?
I will be running accel Gen 7 but that's just the ECM . I am not running their regulator or fuel pump, etc.
Is there a difference with how the injectors perform with pressure difference? I can imagine there is but....?

most of the later model LS stuff is all 58 psi. I have heard the reason they did that was because they also went to returnless systems and the higher pressure helped avoid any vapor lock issues. (actually they still return, but the regulator is built into the fuel filter and bypasses there instead of going to the fuel rails and then bypassing to the tank.

With that said I don't think there's any issue running the higher psi as long as the tune is set up for it; if you convert from a 43 psi tune to 58 psi the higher pressure will make it richer and require re-tuning.

Jody

[Denvervet]

Good points. Makes sense that if one has an ECM with preset tuning then changing pressure would be an issue. With many aftermarket ECMs being tunable one could adjust as needed. thx

[supremeefi]

Originally Posted by camcojb

most of the later model LS stuff is all 58 psi. I have heard the reason they did that was because they also went to returnless systems and the higher pressure helped avoid any vapor lock issues. (actually they still return, but the regulator is built into the fuel filter and bypasses there instead of going to the fuel rails and then bypassing to the tank.

With that said I don't think there's any issue running the higher psi as long as the tune is set up for it; if you convert from a 43 psi tune to 58 psi the higher pressure will make it richer and require re-tuning.

Jody

That's not entirely true. On most aftermarket systems once the O2 turns on it'll correct to the programmed air/fuel ratio. The only time it fattens it is in cold start or any other condition that the O2 isn't operating in. Most injectors are rated at 3 bar or 43.5 psi, that's why most regulators are set at that. Some older style injectors get slower as you increase pressure. Doesn't mean much on a programmable Sequential ECM like the Gen 7 but on others it can effect performance, especially at idle. Increased pressure can enhance the spray pattern and atomization though on some injectors, just depends on the type.

OEM stuff works differently. Most of it is programmed to run at stoich throughout much of the rpm range. However they will run richer in power mode with more pressure cuz the O2 turns off and goes to as premapped fuel curve.

If you need help on your Gen 7 let me know. I'm the guy on their website.

Mark

[camcojb]

Originally Posted by supremeefi

That's not entirely true. On most aftermarket systems once the O2 turns on it'll correct to the programmed air/fuel ratio. The only time it fattens it is in cold start or any other condition that the O2 isn't operating in. Most injectors are rated at 3 bar or 43.5 psi, that's why most regulators are set at that. Some older style injectors get slower as you increase pressure. Doesn't mean much on a programmable Sequential ECM like the Gen 7 but on others it can effect performance, especially at idle. Increased pressure can enhance the spray pattern and atomization though on some injectors, just depends on the type.

OEM stuff works differently. Most of it is programmed to run at stoich throughout much of the rpm range. However they will run richer in power mode with more pressure cuz the O2 turns off and goes to as premapped fuel curve.

If you need help on your Gen 7 let me know. I'm the guy on their website.

Mark

that's not entirely true............ Do you tune a car just enough to get it so closed loop can add or subtract and keep the desired a/f? Or do you tune it so the add/subtract from the O2's is minimal when in closed loop? Bottom line, bumping pressure from 43.5 to 58 psi is going to richen the a/f, and should be accompanied with a tuning change. My humble opinion anyway..........

Jody

[supremeefi]

Originally Posted by camcojb

that's not entirely true............ Do you tune a car just enough to get it so closed loop can add or subtract and keep the desired a/f? Or do you tune it so the add/subtract from the O2's is minimal when in closed loop? Bottom line, bumping pressure from 43.5 to 58 psi is going to richen the a/f, and should be accompanied with a tuning change. My humble opinion anyway..........

Jody

I tune it for minimal correction so if you bump the pressure and the O2 is correcting it'll correct right back to the preprogrammed air/fuel, period.

If it's tuned to where the O2 has a big correction to begin with then yes it will fatten it, only because the O2 runs out of room so to speak.

[camcojb]

Originally Posted by supremeefi

I tune it for minimal correction so if you bump the pressure and the O2 is correcting it'll correct right back to the preprogrammed air/fuel, period.

If it's tuned to where the O2 has a big correction to begin with then yes it will fatten it, only because the O2 runs out of room so to speak.

my point was that if it's tuned for minimal correct and then you bump the pressure that much, it will no longer be tuned for minimal correction.... You are correct, should have enough room for the O2's in closed loop to correct it, but my point was that it will change the O2 correction and a tuning adjustment will be needed to get it back as close as it was. Not saying it won't run. Just saying I would tweak the tune to get it back to optimal.

Jody

[supremeefi]

Originally Posted by camcojb

my point was that if it's tuned for minimal correct and then you bump the pressure that much, it will no longer be tuned for minimal correction.... You are correct, should have enough room for the O2's in closed loop to correct it, but my point was that it will change the O2 correction and a tuning adjustment will be needed to get it back as close as it was. Not saying it won't run. Just saying I would tweak the tune to get it back to optimal.

Jody

O.K but you said it would run richer, it won't, not if the O2 has enough room to correct.

The opposite is true when someone has tuned it for minimal correction and then you use fuel with more ethanol in it, guess what, it'll have to add fuel. But as long as it was done correctly there shouldn't be an issue, no more so than an older EFI'd car that was calibrated for 100% petroleum based fuel and now runs on todays 90/10.

[camcojb]

Originally Posted by supremeefi

O.K but you said it would run richer, it won't, not if the O2 has enough room to correct.

well, it will run richer during warm up, cold start, and any open loop areas. That's also a big "if" on if there's enough room for the O2 to correct. Should be I agree.

We're not disagreeing, just playing semantics. My point was raising the fuel pressure will affect the a/f and I would re-tune to compensate to get my trims back in line and to get my cold start and open loop areas back where they need to be. But you are correct in that there should be enough correction available in the O2's to at least keep the closed loop areas in line, but again that assumes the tuning is right in the first place. If the O2's are already maxed out or close to it, and are pulling a bunch of fuel in closed loop to maintain the desired a/f then raising the fuel pressure will cause it to run richer then desired all the time...........

I do appreciate your info and feedback.

Jody

[Denvervet]

Thanks for all the input guys Didn't mean to start something...lol Supreme once I get my project to that point I just my hire you to help some. I do have a person that came highly recommended and well versed in Gen 7 stuff lined up locally. After reading some posts here even expert (?) people can struggle with this Gen 7 stuff.