[Diy_efi] Donegan ECU, subject of fuel returns and failures

[Mike]

FWIW,

Some 15 years feedback on the return fuel system of the VL Commodore
with the low pressure in tank pump and the high pressure external pump
which feeds into a pulsation absorber (some people confuse this with a regulator).

This has a simple fuel pressure regulator on the exit of the fuel rail and the
pressure regulator reference is off the inlet manifold so the injectors get
fixed pressure across them regardless of boost,  on mine that goes to 10.5psi
and others have seen it at 13psi) For hot starts there is a small cannister
than holds the last highest manifold pressure (ostensibly from boost) and
it holds it for well over an hour without any problem. The ECU switches
a solenoid to apply this pressure to the sense for the pressure regulator
instead of manifold for the first few seconds of cranking and the whole system
works really well and has done for over 20 years...

However, many people who have the T3 turbo setup and go one better with
higher boost occasionally complain of leaning out or erratic performance
and the first item to blame has almost always been the fuel pressure regulator.
Also after a few years of inadequate service the n/a guys complain of lagging
performance and occasional engine damage from running too lean...

However, on 95% of the times I have followed through the service rationale it
turns out to be in order of decreasing frequency of problems:-

!!!!!  Fuel filter blocked with carbon granules/fibre glass threads/resin/gluey goo/silastic
!!!    Broken(Squashed)/Blocked strainer at intank fuel pump inlet.
!!!   Seized low pressure intank fuel pump.
!!    Internally leaky high pressure fuel pump (where the recirculating ball mechanism is badly worn)
!     Cracked  fuel pressure sense line hose
!     Pinhole in fuel pressure sense line (presumably acting as one way valve)

In the remaining 5% of times the fuel pressure regulator has been replaced but, has been found
to make little if any difference, suffice it to say the regulator is the non adjustable type.
In my experience with trying some 4 such regulators on my car over the last 10 years I
have noticed negligible difference in fuel pressure and performance, the most common
failure has been fuel filter and low pressure pump by far with occasional high pressure pump leaks.

Interestingly when people first got onto forums discussing these issues some 10 years ago,
people used to mouth off the value of "rising rate regulators" of course they were not aware
of  the issue of differential pressure and it was quite amusing watching the debates get
ever more heated over this simple point, especially when people starting to push 25psi
boost remonstrating the regulators fault also cracking the plastic housings of the injectors etc...

Having been through electronic engineering some 24 years ago and laboured with control
systems theory, I dont like the chance of making a PWM (PID) type control run effectively
if the pump is some way from the fuel rail, in any case you would need a smart filter to remove
the pump pulsations and reflections from the injector closings. Kalman filters come to mind as
you are doing a sampled data system, I wish you a lot of luck - though being a qualified
machinist would (I thought) have put you in better stead making good fuel delivery and
return lines along with a pulsation absorber allowing your intellect to attend to more
useful issues...


Rgds

Mike
ps Yes Bernd, I trimmed things a bit ;)



At 11:26 AM 1/5/07, "Steven P. Donegan" <donegan at donegan.org> wrote:
>Well, since I am asking for feedback you can call it ugly if you
>wish :-) For me doing just about anything in electronics and software is
>far easier than doing it in metal (and I am a fully qualified machinist
>as well as an electronics/software dude). Given this will require one
>more mostly passive input conditioning circuit and one PWM output
>circuit I may add it on general principles. And thank you for the
>feedback!



Regards from


Mike Massen
Network Power Systems
Lab 08 9444 8961
Mb 0438 048961
Perth, Western Australia
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