[Diy_efi] New project

Dennis Noordsij dennis.noordsij at wiral.com
Mon Nov 18 14:32:35 GMT 2002


> The most fundamental table in a GM SD setup is the VE table, indexed by
> RPM and MAP.  Then there are adders for sudden changes in TPS, for
> coolant temp, for throttle near WOT, etc.
>
> Keep us posted, I'd like to hear how it turns out.
>
> --steve

Hi,

The TBI body is there, with an adapter piece in the works to mount it on th=
e=20
intake manifold. I've been thinking about installing EFI on car/boat for=20
almost a year now, reading all I could find, but always got held back by th=
e=20
mechanical/machining/finding components parts. Guess now I have to fulfull =
my=20
part of the deal though :-)

One thing you mentioned, a VE table for SD. If you take the MAP, compare it=
 to=20
the ambient pressure, isn't there a nifty formula that takes the size of th=
e=20
throttle opening and angle of the butterfly to calculate exactly how much a=
ir=20
would have moved in due to pressure differences? Which would give you the=20
exact amount of air almost as accurately as a MAF could? Every time you=20
receive a TACH pulse, take the time that has elapsed since the last pulse, =
do=20
the math, inject the fuel. I.e., where does the VE come into play?=20

I kind of though the SD using MAP+RPM would mostly eliminate the need for V=
E=20
tables, might as well go with Alpha-N then?

Boat only has one forward gear, is always propped to reach max RPM and no m=
ore=20
at WOT, never goes uphill, never goes downhill, and is always under load=20
(though, because of the different curves of engine power and power needed t=
o=20
rotate the prop, cruise RPM allows the engine to run at 50-60% of throttle=
=20
only).

So, MAP+RPM+whatever other sensors, ambient pressure, humidity, air temp,=20
calculates A/F ratio. Idle is controled by a stepper and maintained at 800=
=20
RPM, cranking enrichments, cold engine enrichments, maybe fast idle (these=
=20
babies heat up FAST though), and TPS for PE.

Megasquirt looks like a great project, and I'll keep it in mind as a backup=
 in=20
case I get in over my head :) MS suits a much wider variety of conditions=20
than I need to deal with, but there is plenty in terms of algorithms and=20
designs to learn from.

Like I said before, it's for-fun, to actually build an EFI setup ourselves.=
=20
The point is not to end up with EFI, which could be done much more=20
painlessly, but to build it from scratch.

Cheers,
Dennis

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