Will an AFPR make your car run rich and use more gas, especially during city driving, than the stock fuel pressure regulator? I use my car as a daily driver and have fun with it once in a while. It does not get on the highway very often. I was told by a mechanic an AFPR would use more fuel, foul plugs and affect the catalytic converter for my use. I thought an AFPR would just increase the fuel pressure and provide for better atomization. Pulse width is controlled by the ECM and will determine how long the injector is open. Please give me your thoughts.

 

The car will run slightly richer in open loop, with a higher fuel pressure. Once the engine acheives closed loop, it starts paying attention to the O2 sensor, and will adjust for the higher pressure.

I actually got better mileage going from 40, to 48 psi at idle. (vacuum line disconnected) Your results may vary. Play with it, and see what works best for you.

 

There was an ad in Summit about the AFPR's and one of them said that not only better power but better fuel economy would be achieved. Happy to see that you may have some evidence to back that up.