Bosch Motronic AFM Spring Tension - Further Comments

[Brad Anesi]

Herewith the opinion of Don (ex-Alfa, now Fiat R&D):

The EFI discussion is difficult: one must first know if the system is
analog or digital and to which degree of autoadaptivity is provided.
Example: Fiat uses/has used _many_ executions of Bosch Motronic
alone, many L-Jet, Monotronic, Weber-Marelli, Rochester, Hitachi....

Maybe this will help:

1. Forget that the closed loop O2 sensor function will correct, in the
end, any minor changes upstream. It will, but that does not seem to be
the issue. We talk open loop.
2. Spring tension makes a difference only during _transient_ movement
and will enrichen until steady state, where it has no effect. There is no
effect at WOT as you are already using the longest pulse found in the
look-up table (MAP) for that set of parameters.
3. Remember, electrons are faster than air!
4. The base calibration is not always based on vane position: depends
on system.
5. Even open-loop, later generations use autoadaptivity, which further
permits default corrections for components operating outside their spec.
ranges, within the ROM map.
6. Aside from AFM vs inputs to controller, this signal is further
corrected by rpm, load, temps, etc., always cross-checking table for
correct fuel delivery before the O2 sensor.
7. To see the effects, get a J.C. Whitney A/F checker.
8. In systems with separate ignition controllers, more benefits can be had
by changing the spark map.
9. Significant changes cannot be made by DIY, nor without a dyno.
10. Perceptions and stop-watch times do not always concur.
11. There are other ways of increasing fuel delivery such as raising rail
pressure, larger nozzles, with larger AFM. But the intake runners and
valves have to be sized accordingly.
12. Our experiences with DIY modified EFI systems do not yield
measurable differences.

Conclusion: for DIY, it seems more cost effective to use carburetors and
a modern ignition system, leaving original EFI system intact for use later
at resale.