Air flow meter modification

[Todd Knighton]

Andrew,
	Good try but won't work.
	Take this example, at closed throttle and idle the engine flows x-cfm
vs Wide Open Throttle (WOT) at idle or 1000 rpm flows y-cfm.  Both these
flows are very low due to low rpm, you can calc it out for engine
displacement and rpm's to find your exact numbers.  Now take the same
two conditions at 7000 rpm's.  Closed throttle is still a fairly low
number, albeit about 7 times idle speed and WOT produces again
approximately 7 times the WOT number at idle.  So if you used the
original code and got the thing wide open at 1000 rpm's the engine would
flood, and become linearly leaner with an increase in rpm's.
	A hot wire with approximately the same flow curve would be a much
better way to replace the AFM with little to no restriction.  You could
send your AFM to Best Products and have them try to calibrate a Ford hot
wire to match the curve of your current AFM, then you would just have to
replace the Inlet air temp sender with some sort of variable resistor
that you could fine tune the air fuel ratio with.  Hot wires don't need
the inlet air temp because they read mass not cfm and don't need the
correction factor.

Godd Luck

Todd Knighton
Protomotive Engineering

Bosch, AN, Andrew, Dr wrote:
> 
> The L-Jetronic has a flapper type air flow meter. If one measures the
> resistance along the graphite? track, it seems to change as you move
> a meter along the track in no seemingly logical way i.e the reading
> increases, then decreases, then increases again, etc Thats one
> question. The next is that I was wondering why the following
> shouldn't work: remove the A/F meter and remove the board with the
> sweeper. Then connect the board and sweeper dirctly to the shaft of
> the throttle body. As the throttle opens, there will now be a direct
> drive to the old A/F meter "mechanism". Only problem that I can think
> of is that the relationship between the amount of opening of the
> throttle  and the movement generated at the "old" A/F meter mechanism
> will not be the same as in the "normal" set-up. So I figured that some
> sort of gearing system could be built in, so that eg when the
> throttle is half open, the A/F meter mechanism is fully across its
> sweep. I thought of doing this electronically, but then came up with
> the problem presented at the start of this post, namely that there
> does not seem to be a linear change in resistance in the A/F meter
> mechanism. The reason for all this, of course, is to try and do away
> with the very restrictive A/F meter.