MicroSquirt.com read only forum (Jan.15,2018)

Hey guys,

I was given a proposal by our formula SAE team:

To design a feedback control system where you regulate pressure in the rail by measuring the pressure using a sensor and modulating the power applied to the fuel pump.

Then you could use a map sensor (or TPS in our case) or rpm as an input thus adding an additional tuning parameter of fuel rail pressure VS RPM or MAP or TPS (or all 3) curves.

Im weighing up the pros and cons at the monent...

Ive been asking around trying to get quotes for a 0 to 10BAR fluid pressure sensor so far i havent been able to find anything < $350(AU).

I was told that a latest model ford focus used this principal, but then i was lucky enough to score the wiring drawings for the whole model range and found that only the diesel models use this form of fuel pressure control.

I could probably use an OEM (to reduce cost) fuel rail pressure sensor of some other late model diesel and give it ago - but i would need some sort of compressor jig with an analouge gauge to work out the Pressure / voltage graph of the sensor.

I was thinking too this might aid some of the problems with fuel injecting motorcycle engine where due to high RPM you get issues with injector small opening times.

what do you think?

davo5 wrote:...I was told that a latest model ford focus used this principal, but then i was lucky enough to score the wiring drawings for the whole model range and found that only the diesel models use this form of fuel pressure control...

All post-2002 U.S. Spec Zetec (2.0L) motors use a returnless fuel rail system. All post-2003 Neon's use a similar system. I'm not sure what AU spec cars would have that kind of system.

The systems I've seen and read about use a constant voltage/varying pulsewidth signal to the pump that changes based on pulsewidth.

For a race car, you're probably in the best position to use this kind of technology. There are very few opportunities for the fuel to sit or cavitate at the consistently high volumes you'll experience.

Something to consider: these systems vary the output of the fuel pump to supply a given volume to meet consumption at a constant pressure. They are not designed to vary pressure and in fact have bypass valves at the pump outlet to protect against an over-pressure situation cause by a blockage or during a "fail safe" mode where the ECU to FPC (Fuel Pump Control unit) communications are lost.

-Brian

thanks for the reply.

So they do pressure feedback control more to maintain a constant pressure, and prevent any drops / increases in pressure which may deviate the mixture from what they want (when not under EGO feedback control i guess?)

I know some MOTEC fuel injection computers use fuel rail pressure compensation when calculating injecting dutycycles.

Its probably cheaper from a manufacturing point of view too, its one less pipe to run through the car and removes the need for a pressure regulator.

I called ford australia and im guessing because the 2.0ltr zetec and diesel combinations arnt available in australia they didnt have a rail pressure sensor in their spare parts catalouges.

Dont suppose you mind doing me a big favour and calling ford US, pr a price on a fuel rail pressure sensor?

hmm just thinking, if the system is designed to maintain a single constant pressure - then the pressure sensor will probably have a hysteresis kind of curve - similar to a narrow band EGR - which will make an OEM sensor unappropriate.

I could still use it on the race car for the same benefits of maintaining a constant rail pressure - and removing the pressure reg and return line full of fuel might have a small weight saving.