[Diy_efi] Donegan ECU
John Gross
jogross3
Fri Jan 5 20:51:02 UTC 2007
Well we need to make sure that we don't confuse pressure with flow. My
understanding through the little bit of the thread I've read so far is that
the intent of the PWM fuel pump control was to reduce the flow into the
rails, not the pressure. Remember that the fuel delivery through the
injector is a square root function of the fuel pressure. If you increase
the fuel pressure by a factor of 2, you will only increase the flow by the
square root of 2. To double your flow, you need to quadruple your pressure
(roughly). Now, if you intend on including a fuel pressure correction
factor in your programming, this is not so much of a problem, though the
engine would likely shut off if the fuel pressure sensor failed. If you are
trying to regulate FLOW with the PWM controller, then you would still want a
mechanical regulator on the system. There are tried and true mechanical
regulators on the market that can and will hold stable fuel pressure to
within about 0.5 psi without breaking a sweat. This type of setup would
give you several benefits to using PWM control for pressure. 1 is that you
don't have to worry about including a fuel pressure correction factor into
the main fuel table. 2 is that your programming is no longer dependent on a
sensor that does not go through the same rigorous QA testing and
certification that TPS sensors go through. Think about the relative
frequency of pressure sensor failures compared to TPS sensor failures.
If your PWM idea is designed around saving the pump over time to make it
last longer, what you can do if you so choose is to use the mechanical
regulator to help you set your operating fuel pressure. At different load
conditions, you can adjust the PWM control on the fuel pump and back the
pump down until your pressure starts to drop. Remember that most pumps will
have a flow rating at free flow and a flow rating at a given psi. You can
back your pump speed down until your bypass through the regulator is
minimal, which can easily by identified by slowing the pump down until the
pressure drops. At part throttle conditions, you will be able to slow the
pump down quite a bit before the pressure starts to drop. Once the pressure
begins to drop, you no longer have fuel bypassing through the regulator, and
you are now at your minimum pump flow to supply the engine at that
programmed injector pulse width.
If this is the methodology that you choose, you must remember that the pump
must speed up quickly in response to throttle tip-in in order to maintain
the new minimum flow. You can do this by either allowing large values for
your accel enrichment, or by giving yourself a larger safety factor for your
minimum flow pump speed (allow more bypass through the regulator), which may
make the additional accel enrichment unneccesary (additional in relation to
a conventional constant net-flow fuel system). Either way it would be a
good idea to have some sort of dV TPS logic built into the PWM control that
looks specifically at your rate of throttle change to control your pump
speed.
My 2 cents
John
>From: "Steven P. Donegan" <donegan at donegan.org>
>Reply-To: diy_efi at diy-efi.org
>To: diy_efi at diy-efi.org
>Subject: Re: [Diy_efi] Donegan ECU
>Date: Fri, 05 Jan 2007 11:12:22 -0800
>
>Well - I was thinking 'simpler' - ie with injectors of X capacity
>subtracting 5-10% of pressure or adding that same would provide a bit of
>tuning capacity. A CPU and pressure sensor and PWM pump control can
>likely beat the pants off a mechanical regulator - but that is my thesis
>and I can certainly be persuaded :-)
>
>On Fri, 2007-01-05 at 18:58 +0000, John Gross wrote:
> > I would say that if you're talking about doing PWM control of the fuel
>pump,
> > and controlling it based on fuel demand from the engine, you need to
>make
> > sure that the software side of the ECU will allow for quite of bit of
> > adjustability in the acceleration enrichment. If you wait for either a
> > specific TPS or a dTPS in order to speed up the pump, if you don't have
> > enough adjustability in the accel enrichment, you'll find the engine
>flat on
> > it's face during tip in. Remember that from the time the TPS registers
>a
> > certain delta and the pump begins to speed up, the entire fuel system
>has to
> > catch up. You might be surprised by how quickly you'll drop pressure at
>the
> > injectors if the pump flow is insufficient.
> >
> > John
> > former Rolex DP Engine Tuner
> >
> >
> > >From: "Steven P. Donegan" <donegan at donegan.org>
> > >Reply-To: diy_efi at diy-efi.org
> > >To: diy_efi at diy-efi.org
> > >Subject: Re: [Diy_efi] Donegan ECU
> > >Date: Fri, 05 Jan 2007 10:45:26 -0800
> > >
> > >And BTW my Mustang has a ~300 lph pump in it now (Holley Black
> > >professional model) :-) A4 4 bolt mains block at 4.0 bore, 342 cubic
> > >inches with a nascar stroker crank, 8:1 CR and 15lbs of B&M Roots style
> > >blower - and of course it's not street legal here in the peoples
> > >republic of CA... Will likely yank the engine and put it in something
> > >pre-1972 so I can daily drive it again...
> > >
> > >On Fri, 2007-01-05 at 12:26 -0600, cobraman at insightbb.com wrote:
> > > > I would like to see a PWM controller with a different purpose - say
>a 2
> > >speed version - then you could use a 1000 HP pump on the street w/o
>beating
> > >the fuel until it boils. Run the pump, with a regulator, at say 50 lph
> > >until full throttle or boost starts, then kick it into high...... just
> > >food for thought. TomS
> > > >
> > > > ----- Original Message -----
> > > > From: "Steven P. Donegan" <donegan at donegan.org>
> > > > Date: Thursday, January 4, 2007 12:41
> > > > Subject: Re: [Diy_efi] Donegan ECU
> > > > To: diy_efi at diy-efi.org
> > > >
> > > > > Well - for track days I simply put dry ice in my fuel cold-can
> > > > > thing -
> > > > > that solves most vapor-lock style problems and lasts for a
> > > > > couple of
> > > > > hours. Simple low-tech solution to that problem. Given the lack of
> > > > > response to my original posting I believe providing PWM fuel pump
> > > > > control and support for a fuel pressure sensor is useful.
> > > > >
> > > > > Given that I normally run at Willow Springs or Buttonwillow
> > > > > during the
> > > > > winter months temps are not normally a factor anyway.
> > > > >
> > > > > On Thu, 2007-01-04 at 12:23 -0600, cobraman at insightbb.com wrote:
> > > > > > My "Edelbrick" ProFlow has fuel pressure controlled with
> > > > > engine vacuum. On track sessions on very hot days, the fuel in
> > > > > the rails will boil under hard braking - accelerator closed (low
> > > > > fuel pressure). When you finally step on it (52 psi), nothing
> > > > > happens until the vapor "recirculates" or is expelled.
> > > > > Usually takes a second or so. I don't think dead heading
> > > > > would do any better - probably just need to keep a constant fuel
> > > > > pressure.
> > > > > > IMHO, hot fuel should give better economy - easier to vaporize
> > > > > - for those green members. TomS
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > ld
> > > > > > > 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?
> > > > > > >
> > > > > > > On Thu, 2007-01-04 at 14:56 +0800, Mike wrote:
> > > > > > > > Isnt one of the main needs for fuel return the fact the
> > > > > fuel
> > > > > > > is heated quite a
> > > > > > > > bit in the fuel rail whilst its waiting for injection ?
> > > > > > > >
> > > > > > > > Of course there is a commercial factor as fuel returns
> > > > > used to
> > > > > > > be so
> > > > > > > > much cheaper than any electronics but getting around the
> > > > > fuel
> > > > > > > heating etc
> > > > > > > >
> > > > > > > > Also the issue of control feedback is an issue to avoid
> > > > > > > vapourisation> during hot start, the good thing about return
> > > > > is
> > > > > > > this can be flushed out,
> > > > > > > > and esp for a turbo as a pressure hold tank can "remember"
> > > > > the last
> > > > > > > > max pressure and temporarily raise the fuel rail pressure
> > > > > to
> > > > > > > this during
> > > > > > > > start to avoid vapour issues... etc
> > > > > > > >
> > > > > > > > Regards
> > > > > > > >
> > > > > > > > Mike
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > At 07:23 AM 1/4/07, you wrote:
> > > > > > > >
> > > > > > > > >This sounds cool...is closed loop control of fuel
> > > > > pressure an
> > > > > > > oem feature for any new vehicles? Or just something you are
> > > > > > > trying out? Are you going to use a PI controller? I am
> > > > > guessing
> > > > > > > when you snap the throttle open the PI controller should
> > > > > know
> > > > > > > about this quite quickly...not wait to see a drop in fuel
> > > > > > > pressure?
> > > > > > > > >
> > > > > > > > >> To add something somewhat useful to the list in this
> > > > > reply
> > > > > > > I'll say the
> > > > > > > > >> Donegan ECM is coming along nicely :-) The input board
> > > > > is
> > > > > > > going to fab
> > > > > > > > >> out at about 3.0 inches by 2.2 inches (exactly matching
> > > > > the
> > > > > > > CPU board -
> > > > > > > > >> ARM based Steve). Inputs designed in are MAP, MAT,
> > > > > > > Barometric, Coolant,
> > > > > > > > >> Throttle, Oil pressure/temp, 4 ea O2 sensors, Crank and
> > > > > Cam
> > > > > > > position, 2
> > > > > > > > >> ea EGT sensors - well pretty much everything everyone
> > > > > told
> > > > > > > me should be
> > > > > > > > >> sensor inputs. Fuel pressure input I'll put on the
> > > > > 'relay'
> > > > > > > control board
> > > > > > > > >> - that will do PWM control of the fuel pump eliminating
> > > > > the
> > > > > > > need for a
> > > > > > > > >> regulator or return line.
> > > > > > > > >>
> > > > > > > > >> Happy New Year :-)
> > > > > > > > >_______________________________________________
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