PWM fuel pump

[Tom Sharpe]

Jeffrey T. Birt wrote:

> Hi all,
>
>     I'm new on this list so this is the first post that I have seen on the subject
> of controlling pressure via PWM of the pump.  It seems that trying to control a
> pump this way would cause premature failure of the pump.  Generally starting a
> pump (of any type) is much harder on it than continuos operation.  PWM would stop
> the pump and then restart it under load.  It would be much harder on the pump to
> start it with 30 lb or so of pressure
> against it.

> IMHO, the pump never stops, just runs slower....

>    Next, picture this scenario.  Your tooling along @ 20 mph and your pump is
> developing (x) lbs. of pressure.  You then mash the accelerator down and the ECU
> determines that you now need (x+y) lbs.  Currently the fuel system is only @ (x)
> lbs., when you accelerate you are effectively lowering the restriction that your
> pump is developing pressure against.  The duty cycle of you injector(s) go up.
> More fuel in the same time period equals less restriction.  The pump has to
> compensate for the sudden loss of pressure (x) and try to build up even more
> pressure (x+y).  This situation will lead to a lag in fuel pressure on sudden
> acceleration.

Hopefully, the pump will respond in milliseconds, the controller in nanoseconds - as
fast as the injectors.

Tom S