[CarlC]

Thanks to Dave for chiming in on issues that can create bald spots for those of us that have enough hair to pull out.

As port injectors and mechanical pumps (LT engines) open/close they send pulses into the fuel. These pulses (high and low) can be picked up by the fuel pressure sensors, and the PWM control system will react fast enough to chase them, hence creating a wildly changing fuel pressure. The controller is essentially turning completely on/off as it chases the pulses.

Mounting the fuel pressure sensor in the rear allows the flexibility of the lines and the column of fuel to act as a pulse damping system. In rare cases where the pulses/fittings/lines/injectors/etc. all "line up" just right the system still chases the pulses. In these cases a Radium Engineering pulse damper cures the troubles.

We have instrumented the pressure loss in a 3/8"/AN6 typical fuel line system. Using my Camaro as the test mule, there are a total of 14 interfaces from the point where the #1 sensor is mounted at the outlet of the pump and the #2 sensor is in the rail + the length of lines. Datalogging was done with HPTuners with separate inputs that allow for monitoring both sensors and to track them with MAP readings. With about 625FWHP supercharged + CTS-V fuel module, the total pressure loss is 2.2psi at WOT. From an AFR standpoint that delta is hard to measure with commercially available equipment and easily taken care of in the tune.

Why the MAP vs. fuel pressure comparison? MAP changes are the first practical and accurate change in the engine that will trigger a change in fuel demand. For a PWM returnless system the changes in volume and pressure can only occur with a change in pump speed. There are valid concerns that the pump speed cannot change as fast as the engine demand/MAP. From a MAP vs. fuel pressure response standpoint, we have found that it's a non-issue. The electric pumps spin up fast enough that there is no concern with them keeping up with engine demand. We're talking less than a few engine revolutions at 6000rpm for the pumps to track with MAP. This has proven out over the last 11 years with zero feedback from customers/tuners of any kind of lean spike due to pressure drop-off due to reaction time.