Fuel pressure?

jimberg · 05-22-2001, 01:03 PM

LX XLR8R, the way you are using your FPR is correct. I have mine set at 47 psi for the same reason. The only effect setting it has is increasing or decreasing the amount of fuel available at the top end. The computer cannot control fuel pressure. That's strictly mechanical.

I was responding more to TheSloAod's message so I didn't cover all of the nuances of adjustable FPRs and how the computer works. I guess I'll go over it again.

The computer has preprogrammed air/fuel settings that it sticks to. It uses the MAF and O2 sensors to keep it at those settings during closed loop operation (normal cruise). While it adjusts the amount of fuel delivered into the cylinders it keeps track of how long it's opening the injectors to keep the correct air/fuel ratio. This information is stored in adjustment tables and is used at WOT when the computer is just using MAF to figure out how much fuel to deliver. If you don't have fuel starvation problems, adjusting your FPR does nothing. That's why it's a waste to put it on a stock engine.

If you're leaning out on the top end like you were, that means you have reached the throughput limits of your injectors running at stock pressure. By increasing the pressure, you are increasing the throughput limits of the injectors and, therefore, making it possible for the computer to do its job by delivering more fuel at WOT.

Our computers are programmed to balance power with cleanliness. If cleanliness wasn't an issue, we would probably have a richer air/fuel mixture for more power. This is why TheSloAod saw positive results as he bumped up his fuel pressure at the track. The computer will see that fuel increase and start to adjust back down to the clean running air/fuel ratio. The next time he goes to the track it will be back to what it normally runs unless he resets the computer before his runs.

If he was having fuel starvation problems, that's a different matter as explained above.

I hope this is clearer now.

------------------
351W 89 Mustang GT Convertible

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05-22-2001, 01:03 PM	#5
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	LX XLR8R, the way you are using your FPR is correct. I have mine set at 47 psi for the same reason. The only effect setting it has is increasing or decreasing the amount of fuel available at the top end. The computer cannot control fuel pressure. That's strictly mechanical. I was responding more to TheSloAod's message so I didn't cover all of the nuances of adjustable FPRs and how the computer works. I guess I'll go over it again. The computer has preprogrammed air/fuel settings that it sticks to. It uses the MAF and O2 sensors to keep it at those settings during closed loop operation (normal cruise). While it adjusts the amount of fuel delivered into the cylinders it keeps track of how long it's opening the injectors to keep the correct air/fuel ratio. This information is stored in adjustment tables and is used at WOT when the computer is just using MAF to figure out how much fuel to deliver. If you don't have fuel starvation problems, adjusting your FPR does nothing. That's why it's a waste to put it on a stock engine. If you're leaning out on the top end like you were, that means you have reached the throughput limits of your injectors running at stock pressure. By increasing the pressure, you are increasing the throughput limits of the injectors and, therefore, making it possible for the computer to do its job by delivering more fuel at WOT. Our computers are programmed to balance power with cleanliness. If cleanliness wasn't an issue, we would probably have a richer air/fuel mixture for more power. This is why TheSloAod saw positive results as he bumped up his fuel pressure at the track. The computer will see that fuel increase and start to adjust back down to the clean running air/fuel ratio. The next time he goes to the track it will be back to what it normally runs unless he resets the computer before his runs. If he was having fuel starvation problems, that's a different matter as explained above. I hope this is clearer now. ------------------ 351W 89 Mustang GT Convertible