Don't feel like taking up more space on here than need be.

First question. An AFPR can increase performance while decreasing MPG. Now on a long trip, can pressure be lowered and have mpg increase?

2nd Question: Does having a barely any gas in the tank make performance suffer? I put in barely less than 2 gallons. Performance was normal, but as soon as I burnt a gallon, performance was noticeably less especially on a take off. Just curious if this is the case or if it's just placebo.

That is all. Sorry if this has been discussed many times, search function is the best on my cell phone.

 

Well for your first question its more complicated that higher pressure more fuel more performance or the reverse less pressure less fuel better economy. Increasing the pressure only results in increased performance only if the car was running lean to begin with. If the car was tuned perfectly or was already rich it would hurt performance. On the flip side it would seem that fuel economy would be improved by decreasing the pressure which should in theory reduce the amount of fuel sprayed into the motor. However this isnt true because reducing the fuel pressure causes the motor to go lean which the ECM will compensate for by having a longer injector pulse. Now you might wonder if thats the case why does increasing the pressure improve performance if the o2 sensor is just going to allow the ecm to compensate for the change? The only reason increasing the fuel pressure could result in better performance is because the o2 sensor readings are ignored at full throttle because the car is made to run on the rich side in those conditions and a narrow band o2 sensor cannot read that accurately. If you want better gas mileage you could reprogram the prom to run leaner at cruise conditions/idle but i dont think the gains would be note worth. As far as the gas tank is concerned if you truly only had 1 gallon in the tank the fuel pump could easily have troubles picking up fuel. Not to mention running that low isn't really recommended as the fuel pumps use the fuel for cooling and lubrication in many cases which mean low fuel levels like that could damage the pump.