-

<snip
Sounds good I'll try that first.
I was thinking of changing the frequency to change the leaning. Easier
than changing the MAF output.

Paul Lamar

Paul -

Depending upon the circuit you use this may not work.

1) If you select a simple duty-cycle circuit (like the one I linked to
yesterday), varying the frequency won't change the fuel injected.
Example using a 40/60 duty cycle:
200Hz = 5ms;  2ms on, 3ms off
100Hz = 10ms; 4ms on, 6ms off
50Hz  = 20ms; 8ms on, 12ms off
Running for 1 second (at any frequency) results in 400ms of "on time".
200Hz: 200 * 2ms = 400ms
100Hz: 100 * 4ms = 400ms
50Hz:   50 * 8ms = 400ms
Therefore varying frequency will have a negligible effect on mixture
(except at the extremes).  This WILL NOT function as a mixture control.

2) If you generate a MAF-proportional-pulse on an adjustable trigger
clock (which is another approach altogether), then varying the clock
trigger freq will have a proportional effect on fuel injected.  This
WILL function as a mixture control.

For the sake of discussion clarity, it would be best if you declared
which approach you are going to try.  Both of the above variations are
simple compared to RPM feedback schemes.

I think your goal is a simple fuel injector controller.  Your
adjustable trigger clock idea (#2 above) would involve a second 555
timer (one as a trigger generator, another as a pulse width generator).

In a single 555 circuit, I think simply playing with RC values to vary
pulse freq will not affect the duty cycle.  Then again, the 555 is so
VERY flexible, maybe there exists a circuit variation to do what you
want.

-Vince Orton

You are changing both. The pulse width at a given RPM and a given flow
is fixed by the mass airflow sensor. More often more fuel less often
less fuel.

Paul Lamar