OK, I've had my
ecometer since 24-June-09 and have now gone through four tank-fillups, so it's time for a review.
1) of its four operating modes (MPG-inst, MPG-avg, MPH, RPM), only the
MPG-avg seems truly useful (displayed values on the other three modes "jump" around too much to be really usefull).
2) it has a
single calibration setting (EFF=XXX) which seemingly affects only the MPG-inst and MPG-avg readings. It comes preset with EFF=100, but can be adjusted anywhere between 60-and-140...and, although the EFF-number entered/displayed is an integer, I'm suspecting that it actually represents a decimal-place efficiency value, ie: 100 = 100% = 1.00, etc.
3) the OEM preset EFF=100 produced MPG-avg readings that were too high:
tank#1 0.893 = (1.00)*(34.1mpg/38.2MPG)
tank#2 0.861 = (1.00)*(32.1mpg/37.3MPG)
tank#3 0.935 = (1.00)*(34.5mpg/36.9MPG)
...so, I tweeked the setting down to EFF=90, which yielded a closer correlation between the tank-fillup mpg value and the ecometers' MPG value:
tank#4 0.887 = (0.90)*(33.8mpg/34.3MPG)
...so-o-o-o-o, apparently, the Pontiac (Toyota) 1.8L (2ZR-FE) engine needs an EFF=0.88-
0.90 setting. Next tank-fillup should confirm this.
...although not provided in the owners/instruction manual, here's the basic "calibration" formula:
EFF(new)/EFF(old) = mpg(tank)/MPG(meter)
...so:
EFF(new) = EFF(old)*[ mpg(tank)/MPG(meter) ]
where:
EFF(new) = new calibration number derived from tank-fillup vs. MPG-avg value and old EFF nuimber.
EFF(old) = the calibration number the ecometer had during the test period.
mpg(tank) = value from tank-fillup, ie: mpg = miles/gallons.
MPG(meter) = value from ecomoter MPG-avg display.
4) there are no corrections for distance (MPH) or fuel (GALLONS) values, just the single EFF=XXX value; simple, but not easily "correctable" for multiple changes (tires/wheel sizes, etc.).
5) both the RPM and MPH readings are 3-digits: (a) in 1,000's of rpms, ie: 1.42, so accuracy only to 10's of rpms; and, (b) 64.9 mph...but, both constantly "jump" around by 3 values in the last place, making it a guessing game as to what the actual value is.
...more to come.