coolant
temperature are up to normal operating levels, the ECM uses O2 sensor input
to vary fuel flow so that a 14.7:1 air fuel ratio is continuously maintained.
It accomplishes this by altering Integrator and Block Learn values (also known
as Long Term and Short Term fuel trim), which in turn vary fuel flow as required.
Integrator and Block Learn values of 128 are neutral
and do not instigate any correction to fuel flow. Values of less than 128 indicate
the base fuel calibration is rich and that the ECM is reducing fuel flow; values
in excess of 128 are indicative that the ECM is increasing fuel flow to compensate
for an excessively lean condition. Integrator and Block are automatically set to
128
LEFT: Most injectors look identical externally, and are physically interchangeable,
but differ significantly in flow capacity. Some can be identified by color code;
others have only a part number. Shown from left to right are a Bosch, Rochester,
another Bosch (note difference in tip style), Ford Motorsports "Blue Top,"
"Red Stripe" and Lucas "Green Stripe."
when an engine is first started and remain there until the control system transitions
into closed loop operation. (In some systems Integrator and Block Learn values
are reported as percentages, rather than absolute numbers).
Under ideal circumstances, Integrator and Block Learn
values never vary above or below 128. In the real world, they tend to move a
good bit as the system attempts to compensate for both momentary and long-term
changes in air/fuel ratio. As long as "Learn Control" is enabled (On)
the system automatically administers its
