[Diy_efi] Donegan ECU

[Daniel Nicoson]

I would vote to "keep it simple Sam".  The "normal" return type fuel system
with a mechanical/pneumatic regulator works great, why add complexity?
Remember, you won't b e tuning the car.  It will be some other bonehead that
doesn't fully understand your system.  When he mucks it up, your system gets
blamed.  Keep it only as complicated as it needs to be.

Ford uses the return-less fuel systems and modulates fuel pressure on the
newer Mustangs; and I'll bet most of their other cars.  I think it is to get
emissions that much cleaner, not having warm fuel vaporize...

I have "heard" that some of the 2003 Cobras have problems on shifts with the
pressure spiking and then being too low after the shift.  I don't know how
prevalent this problem really is.  I know there are tuning parameters in the
program code that can be adjusted.

I would suggest that fuel pressure control by PWM of the pump motor would be
too slow except to make up for longer duration events (longer than 2
seconds).  Compared to changing injector PW, motor control is much slower.

My vote, keep it simple.

Good luck with the project.

Dan Nicoson

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
Behalf Of Steven P. Donegan
Sent: Thursday, January 04, 2007 7:49 PM
To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] Donegan ECU

I can't quite read this as a yes or a no to fuel pump pressure control -
can you give me a binary response :-)

I.E. does fuel pressure sensing/fuel pump control make sense for an EFI
system or not.

Thanks!

On Fri, 2007-01-05 at 08:00 +0900, Bernd Felsche wrote:
> On Friday 05 January 2007 00:57, Steven P. Donegan wrote:
> > I had not thought of fuel temp at all - every vehicle I drive
> > would consume the gas in the rails well before it got warm :-)
> > However this does raise a point - perhaps my ECM/PCM/EFI computer
> > needs a way to open a fuel return line and to sense fuel temp in
> > the rails? Any ideas on how useful that would be in the 'real
> > world' anyone?
>
> Superflous if you're running in closed-loop; which you would be if
> the fuel rail was warm enough to make a difference.
>
> If the temperature in the fuel rail is a problem, then a
> recirculating fuel pressure control system is IMNHSO a better
> solution. In such a system, there's always "fresh" fuel that's in
> excess to the amount required for injection from the tank flushing
> the rail(s). The fuel tank is the cooling environment for the fuel.
>
> Pressure regulation also happens at the rail(s), whereas in
> "dead-end" systems it's at the fuel pump, perhaps a several metres
> from the rail and therefore the injectors. That increases the
> difficulty in controlling the pressure (time delays that depend on
> fuel pressure and temperature); especially if it's to vary
> dynamically wrt manifold pressure.
>
> The ability to vary the fuel rail pressure is at least desirable to
> get consistent injected quantities due to a fairly constant pressure
> difference across the injector; between the fuel rail and the
> manifold where it's injecting.  Makes for simpler calculations on
> injected quantity.
>
> If you're stuck with a "dead-end" fuel delivery system, then you
> need to add a return line and a valve that vents the rail(s) back to
> the tank in the interval between the fuel pump running and the
> engine actually being started. The time delay will depend largely on
> the free-delivery rate of the fuel pump and the volume of the fuel
> rail(s). That ensures that there's "cold" fuel in the rail(s) before
> you start injecting it.
>

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