efi555

[Peter Wales]

At 03:57 PM 1/26/96 MST, diy_efi at coulomb.eng.ohio-state.edu wrote:
>In December we had a small thread going on 555 based efi systems.
>This looked like a fun project so I rigged one up on the bench. There
>wasn't alot of detail in the thread so I'm guessing here; I presume
>the 555 was used as a pulse width modulator.
>

Use the Cmos version of the 555 and the control voltage input will be the
"mixture". For the basic version this can be connected to a pot wired as a
voltage divider across the power supply, but later on as the system gets a
cpu to add a microprocessor based control function, it will be connected to
a d-a output for pulse width modulation. The values of components around the
555 should be selected to give a minimum-maximum pulse randge of 2 mS to
20mS so that the full range of RPMs can be covered. There will undoubtedly
be different requirements for different numbers of injectors etc, so this
bit of the design will be upto the user.

The reason for not giving too much detail is the sheer variety of
applications this setup has, and the fact that I proposed it for a very
unusual one of a single injector MGB engine. However, I have built and used
one on a race car and know it works so ask questions when you have problems
and I will do my best to help


>Is there a way to safeguard against run-away? It seems to me that a vacuum
>leak in the intake system could send the engine into orbit, the only limiting
>factor would seem to be the amount of fuel getting passed the throttle plates.

The lack of fuel would stop the engine racing away. Also it would be
possible to incorporate a rev limiter in the cpu design later, or fit it
into the ignition system.


Peter Wales
President Superchips Inc
Chairman Superchips Ltd        "Timing is everything"
Superchips home page with all the answers http://www.superchips.com