MoTeC Screwdriver ECU - Manual (Page 4)

Page 4 of 5
lightly modified engine for maximum fuel economy a figure of 4% is O.K. One problem often
encountered is that, while the gas analyser is adjusted for zero and span, it may not have been
calibrated with span gas of a known CO percentage for some time. We have found a number of
analysers with errors greater than 2% C0, which is enough to give seriously defective information
which you are using to tune your mega dollar engine. Periodic calibration checks with Span gas
minimises this source of error Once you have worked up to full power at 3000 (or 4000 R.P.M.), which
is indicated by the appropriate R.P.M. light coming up, and are happy with the reading of CO
level, we recommend that you stop and record the number displayed by allowing the E.C.U. to
cycle through to the appropriate R.P.M. setting. If the number is high, e.g. 90, the basic range
setting is too low, we would suggest you go up two ranges and, bearing in mind each range
changes the number by 20 units, therefore in this case 2 ranges would be 40 units, which means
that the setting of 90 would have to be reduced by 40 to read 50. On the other hand if the R.P.M.
setting was low e.g. 25, it would suggest the range setting is too high and should be reduced one
range and that 20 should be added to the 25 and therefore should read 45. Having established a
basic setting at one R.P.M., in this case 45, cycle the ECU through and set R.P.M. adjustments below
this R.P.M. range by adding 20 units to higher R.P.M. adjustments e.g. 4000-65, 5000-65, 6000-65,
1000-65 etc. and decrease by 5 units for lower R.P.M. settings e.g. 3500-40, 3000-40, 2500-400 etc.
This will give a fuel curve which may assist in reaching optimum settings a little more quickly than
starting from a random number. Repeat this gradual working up to full load and CO level checking
and fuel adjustment at each other R.P.M. range. The results of excessively rich mixtures over a long
period are washed bores and high ring wear while the results of running with lean mixture for very
short periods are total destruction of the engine - always start with rich settings and creep up to full
power. If using an engine dynamometer that has fast and stable torque read-out, it is possible to
simply dial fuel supply to maximum torque at each speed range very quickly.
LIGHT LOAD
When setting the light load it is suggested that the engine is run at a speed corresponding to the
maximum torque seed but with little load (approximately 1/5 to 1/10 of full throttle torque) to
simulate road load and the adjustment set to the lowest setting that produces smooth engine
operation. On lightly modified engines, this point may correspond to 0.5/. to 1/. CO, but will
probably be more for highly tuned engines. Again this adjustment is carried out only when the red
L.E.D. for the light load is illuminated.
ACCELERATION ENRICHMENT
Best carried out on road. Is applicable primarily to lightly modified engines or engines which
capable of running satisfactory with a lean light load (part throttle or cruising) mixture and
therefore require additional fuel for hesitation free acceleration. The adjustment should be set to
the minimum setting that produces stumble free acceleration from a low speed post throttle
condition.