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Greetings!
Last week I discussed the hesitation my TEC-II-equipped turbo Miata
experienced. This occured during the 40 kPa to 70kPa pressure range transition
with a slow-opening throttle at rpms under 3000 rpm. After Ray A mentioned his
Link-equipped Aerodyne did the same thing, it got me to thinking about
breaking out of the mold of "tune the car to perfection".
Below are the old settings for the TEC-II. The goal is to set the target
air/fuel ratios, and then tune the Volumetric Efficiency table to account for
variations in the engine efficiency. Remember, with a TEC-II, stoichiometric
(14.64:1 air:fuel) is represented with Gama = 1. Gama > 1 is rich (ie 12:1);
Gama < 1 is lean (ie 16:1).
I was trying to get the air:fuel mixture rich enough at 64 kPa to overcome
the momentary lean spot where the mixture would go as lean as 20:1 and the car
would "bog" for approximately 1/2 second *only when the throttle was opened
slowly at low rpms*. It was several months before I noticed this phenomenon
and then it drove me nuts because this pressure range is also used as the
throttle is opened and closed at cruising speed.
Note: for brevity I did not type in the entire Volumetric Efficiency Table.
rpms 1100 2600 3750 4300 5000
pressure
90 kPa 1 .85 .84 .87 1
64 kPa 1.05 1.1 1 .98 .99
40 kPa .85 .88 .88 .95 .95

Instead of trying to bring the mixture to the proper ratio as the pressure
increased, I figured "Why not purposefully leave the mixture rich at lower
pressures in non-idle ranges?" I'm interested in the proper leaning of the
mixture at idle (1000 rpm in my case), I could care less if it is rich
(14.3:1) at 2600 rpm or higher because I don't idle the engine there. The EGO
correction factor attempts to pull these 40 kPa "rich" settings lean but the
settings are rich enough the air:fuel will not go as lean nor for as long as
previously when the throttle is slowly cracked open. Since I neither cruise
nor idle at these rpm/pressure combinations they only affect engine operation
a small percentage of the time.
The new values are:
rpms 1100 2600 3750 4300 5000
pressure
90 kPa 1 .85 .83 .87 1
64 kPa 1 1 .97 .95 .99
40 kPa .83 1 1 .95 .95

Please note I have done what Shiv P refers to as "purposefully detuning" the
engine control parameters.
I estimate 80% of the previous hesitation is now gone; the throttle response
is *much* smoother and I note *no* hesitation at highway cruising speeds of 50
to XX mph. On city streets, lugging the engine under 2000 rpm, I can still get
occasional hesitation but higher rpms (2500) the response is silky smooth.
Low-rpm exits from corners with small throttle openings are much better
behaved.
Again, this "hesitation" was very subtle and it took me months to realize it
was there and then review of data logs to discover the cause. Rapid throttle
movements or any throttle movements at higher rpms caused no discernible
hesitation. The above problem was most noticable in around-town driving.
I believe the above will also work for any other owners of after-market ECUs
who have the same niggling problem.
I also leaned the choke parameters even more and the engine is warming up
with no problems.
Hope this helps someone out.

Regards,
Barry and "Gandalf"
'91 Silver with BEGI turbo and TEC-II