PWM fuel pump

[Jeffrey T. Birt]

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.

    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.

    How about making an electronically controlled pressure regulator.  For
instance the pressure regulator on my Suzuki is controlled via manifold pressure.
It seems that one could fabricate an adjustable air bleed which would affect fuel
pressure.

    IMHO.  YMMV.

Jeff Birt
rauscher at icst.com wrote:

> Getting back on this late... but better then never...
>
> I think your right on the money here Tom, a PIC or small micro is
> the way to go. Due to all the inputs required, and the fuel pressure
> curve desired, doing this in analog is not the way to go.
>
> I have an analog error-amp/charge-pump feedback system working, but
> this will only provide for a single pressure. The pressure requested  is
> by a pot, the real pressure is fed-back via a fuel pressure sensor. This
> would be adequate for a TBI system. A port system would need at the
> least a manifold pressure sensor (MAP) adjustment also.
>
> At this point, I've gots' to get the EFI system fully operational on the car,
> then I can start playing more with this stuff.
>
> BobR.
>
> >rauscher at icst.com wrote:
> >
> >> A possible better use of the PWM system will be to provide a rising
> >> rate fuel pressure. This will allow the pump to relax at idle, and
> >> to run harder as required by the right foot.
>
> Tom S. wrote:
> >
> >Bob and I are on the same wave length. I would like to see a pic driving it
> from a
> >tach lead, MAP sensor and fuel pressure sensor. I would like to see 25 psi
> delta @
> >0-2K rpm rising to a constant 75 psi delta above 6K rpm. Use the maps to tune
> the
> >system from here..
> >
> >This could be a stand alone unit or controlled by an analog signal from the
> ECU..
> >
> >More later when we get the proto's done.
> >
> >Tom S