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

My standard ECU has two fuel pump voltages - one for below certain air-flow levels and one for above. Theres a main fuel pump relay circuit (FC) and a pump speed selector line (FPR) that controls the switch between resistor'd pump feed and straight resistorless feed. Both lines are earthed when fuel pump is at top speed - can anyone see a reason not to earth both through the stock MS fuel pump control? I believe the main relay feed is diode protected but the speed selector isnt, but if they are wired in parallel they'll both benefit from the diode.

Thanks
James

There may be a slight reduction in the lifespan of the fuelpump and perhaps a little more heat put into the fuel at low engine power levels but on the whole the system should still work fine. There are plenty of high power turbo motors running with high volume flow pumps. the nature of the system is such that as the manifold pressure drops, so does the fuel pressure. With fuel pump current being roughly proportional to fuel pressure (at least for a roller cell positive flow pump), the curent drops also, thereby achieving a form of automatic fuel pump power control..

The only major problem would be if the two-level fuel pump scheme was introduced to prevent the fuel pressure regulator from being overloaded by excessive flow rates that could mess with the fuel pressure at low engine power levels (high manifold vacuum). I would be surprised if this was the case though.

OK, thats good to hear. Not too worried about lifespan really. Surely if the pump overwhelms the regulator then, at least with the MS, you could change the VE tables to reduce the fuel delivery, at least to a certain degree?

I would expect that you could and alternatively placing a somewhat bigger fuel regulator should not be a large issue either. Nothing insurmountable..

CB wrote:...Surely if the pump overwhelms the regulator then, at least with the MS, you could change the VE tables to reduce the fuel delivery, at least to a certain degree?

Reducing the fuel delivery would INCREASE the load on the regulator.

Remember, MS is not controlling your fuel pump or your regulator, only the injectors.

-Brian

No but increased load on the reg will simply lead to higher rail pressures, and therefore DC tweaks will counteract the extra flow. Bit of an itterative process but will level out somewhere.