I was reading a car magagzine the other day and they had a 350 tpi with an afpr on it. They turned the fuel pressure up to around 50 psi. They said it wouldn't cause them any real change in gas mileage because the oxygen sensor would make up for the added pressure by changing injector pulse width. I have never heard this before. To get to my point I have an 87 iroc and when the afpr was put on we checked the fuel pressure with the stock one first and it was around 46 psi, then with the new one we set fuel pressure to 36 psi and i gained .3 tenths in the quarter, so does this mean my oxygen sensor was broken when we changed to the afpr. I mean if this is the case i could set the fuel pressure in my 305 to 50psi and go even faster yet. Or can the injector pulse width only go so low? How much variance is there in the ecm for pulse width? Thanks in advance for any info.

 

Hmm... interesting... the whole point of increasing pressure is so that the injectors have the pressure when they need them, they tend to lean out on acceleration. The ECM doesn't need to run them on as high of a duty cycle because of the added pressure keeping them closed, but when they are open more fuel flows through, and because of this you get better atomization and better power...

Thats kinda choppy and thrown together, but I hope you get it... you gained .3 huh... are you usuing fully corrected times, or was it just 15 degrees colder with no humidity when you went for your second run... are your times consistent, you've gotta be having traction problems with that 5.7 if it'sw relativly stock... all these things can attribute to decreased times... my guess that rght now your injectors are running at 100% duty cycle and just making up for the loss in pressure... set it at 50 and see what happens... if you loose power or don't like it, then go back... play with it...

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1985 Camaro SC - 2.8L, auto.

C'mon, spin 'em for papa...
http://www.xenodrgn.f2s.com/Frontright.jpg

 

Sorry Xeno I think that you noticed I said i have a 305 it's down near the bottom, I have an okay understanding of the fuel systems operation. But i don't know why the magazine said that the oxygen sensor would change pulse width to make up for the added pressure, what I mean is that my interpretation is that I could essentially turn the fuel pressure up pretty high as long as it isn't so high it keeps the injectors from opening and I don't burn the fuel pump up too prematurely. I hope someone understands what i mean.

[This message has been edited by AFRO IROC Z (edited October 04, 2001).]