the problem is they do
at operating temp the ecu will keep closed loop operation untill 4500rpm
so even if you stomp on the throtle the ECU is trying to maintain 14.7 to 1 ration across th erpm range until 4500
thank CARB for that
usually in lamens terms the old style used to go to open loop to allow a rich condition to meet the demand of load
sorry no more
thats why you need to interface with the ECU to prevent initial boost lean spot or detenation WILL occur and say good bye to those pistons!!

later from monster pro 5 with 440HP

Ok now I am confused...

The Protege's FS engine switches to Open loop at full throttle, in which a pre-programmed set of fuel maps is used and the rest of the time the system utilizes various sensors to control the air/fuel ratio (closed loop). This is why anything less than a programable piggy-back is useless, and only has an effect in partial throttle...Or so I thought, are you saying that all that 4500 rpm business applys to the Protege's ECU or the older OBD-I (Probe, MX-6, 626) ECU's?

every model before 96 was OBDI

96 and after was OBDII

OBDI normal operation:
open loop when engine is cold
closed loop when engine is warm
wide open throttle : open loop again relyng on MAF and THROTTLE position sensor to provide info on load. then ecu will search pre programed maps to send signal to fuel injectors
closed loop agian when at cruising speeds relying on O2 sensor voltage to maintain A/F ratio


OBDII normal operation (as far as i know every vehicle)
open loop when engine is cold
closed loop when engine is warm
wide open throttle : still closed loop!!! thanks to emmision Standards in the USA. untill the engine reaches 4500 rpm (if it does) then it will go into open loop until the rpm's go under 4500
it uses the O2 sensor to maintain A/F ratio for EMMISION purposes only
CARB in california does not care about your performance
so you need some thing to interface with your stock computer to "manipulate th O2 reading it is sending so that you have enough fuel when you mash the pedal and want to be super man at the track or the street!!!!
hope that helps
need any more info let me know

later from monster pro5

ok thanks

I knew about the OBD II change in 96, but didn't know that much about the Protege's ECU...Some have said that ours goes into Open Loop at any RPM range not just after 4500 rpm, but I didn't know which was correct...

it is one of the most intelligent ecu's on the market
more complex than the miatas
we have been trying to get some info on the language barrier to reprogram the eepromm but so far not to much luck
soon though!
later monster pro 5

great, keep us posted on how it turns out...