[Diy_efi] idle control strategy for SD systems w/o bypass air control?

[pjr at teknology.net]

I had the same difficulty controlling a random, 100 RPM idle roll with a
BDS blown, 355 SBC equipped w/ Accel DFI and 16, 25lb. injectors in the hat
at 40 PSI F/P. I found that giving the engine as much idle spark as it
would tolerate and then dialing back the fuel and spark alternately, gave
me a pretty stable idle w/ only a random 25 RPM roll now. Kinda tuff
controlling fuel on one of those monkeys.......long distance from injector
tip to intake valve, large plenum volume, huge valve overlap and spinning
rotors in the way....etc!   ;-)


Cheers!
PJR
----------------------------------------
----- Original Message -----
From: <socrace at ameritech.net>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, August 27, 2002 12:02 AM
Subject: Re: [Diy_efi] idle control strategy for SD systems w/o bypass air
control?


>     There's another method that I've been using for awhile that
stabilizes
> idle rpm pretty well with or without an air motor.
>     The method can be simply stated as follows: as idle rpm drops, richen
> the mixture in direct proportion to the rpm drop. As rpm rises, lean the
> mixture by the same rule.
>     This works because an idling motor is (usually) pulling air at Mach 1
> through the throttle system. This means that air mass entering the
manifold
> per unit of time cannot change, so the mixture changes with rpm.
>     I believe this is the main reason that an idling engine will stall so
> easily with a sudden load change, as the rpm drops it just runs leaner
and
> leaner.
>     I used this method to stabilize the idle on my Edelbrock Pro-Flo, a
> typical heat soak "blower roll" idler.
> Bob D
>
> On Mon, 26 Aug 2002 07:45:41, you wrote:
>  >Vary the ignition timing.
>  >If man built it, man can crack it.
>  >BobR.
>
>
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