How about no MAF or MAP?

[Josh Karnes]

> My pet project at the moment, is a EFI (& Elec. Ign.) system for my
> Datsun 510 club race car. I've taken one look at your average flap
> type mass airflow sensor (280ZX)

L-Jet.

OK, I wanna get into this discussion, as I have a BMW with an L-Jet 
that I'd love to modify.  Of course, this car has the complete L-Jet 
on there now, with all the sensors and AFM, TPS, etc.  Also, the 
original throttle body.

I don't have to meet any emmissions tailpipe tests or whatever here 
in Austin either, so I am very much interested in ditching the AFM in 
my car.  I assume that after a certain number of rpms, the ECU takes 
over for the miixture curve.  It has to sense this rpm somewhere, 
right?  Which means that there must be some circuitry in there for 
determining injector pulse width based on rpm.  This must also be 
independent of the throttle position.

Is it feasible that you could feed the AFM inputs on the ECU with the 
output of some circuit comprising of a frequency-to-voltage converter 
and some op amps, so you could simulate a condition of the variable 
resistor AFM?  Basically a voltage is applied to the rail of the AFM, 
then there is some resistance, so there is an output voltage after 
the drop through the resistor (there must be a reference resistor in 
the ECU, I guess).  So, with a frequency-to-voltage converter 
sampling pulses from the coil, you can convert the rpms to a voltage. 
 You can then use some sort of variable resistor to find the throttle 
position.  Use these to drive the input of an op amp that can be 
tuned to give a voltage output approximating that of the AFM in the 
same scenario.  This would adjust the pulse width of the injectors 
based both on throttle position and on rpm.  No restriction from the 
AFM either.

Just a thought.  I am sure you guys have been all over mmodifying 
L-Jet EFI, so is there an archive anywhere I can read?  I'd like to 
get up to speed on the state of the discussion before asking a bunch 
of questions that have been answered a million times or bringing up 
topics that have been covered already.

Later-
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Josh Karnes                                                 joshk at tanisys.com
Renaissance Man                        http://www.tanisys.com/~joshk/home.htm
Tanisys Technology                                     http://www.tanisys.com
Austin, Texas                      '78 BMW 530i | '72 Datsun 240Z | IZCC #308
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           *** opinions expressed herein are MINE, ALL MINE!! ***