Jeep J-10 Series 1982 Technical & Service Manual page 425

DIAGNOSTIC PROCEDURES FOR CEC SYSTEM
General
The open loop mode of operation occurs when:
• starting engine, engine is cold or air cleaner air is
cold,
• engine is at idle speed,
• carburetor is either at or near wide open throttle
(WOT).
When any of these conditions occur, the metering pins
are driven to a predetermined programmed position for
each condition. Because the positions are predetermined
and no feedback from the oxygen sensor relative to the
results is accepted, this type of operation is referred to
as open loop operation. The five open loop operations are
characterized by the metering pins being driven to a
position where they are stopped and remain stationary.
Operational Priorities
Each operation (except closed loop) has a specific me
tering pin position and because more than one of the
operation selection conditions can be present at one
time, the MCU (microprocessor) is programmed with a
priority ranking for the operations. It complies with the
conditions that pertain to the operation having the high
est priority. The priorities are as listed below.
• Cold Weather Engine Start-up and Operation
If the air cleaner air temperature is below the cali
brated value of the thermal electric switch (TES), the
stepper motor is positioned a predetermined number of
steps rich of the initialization position and air injection
is switched upstream. Lean air/fuel mixtures are not
permitted for a preset period following a cold weather
start-up.
• Open Loop 2, Wide Open Throttle (WOT)
Open Loop 2 is selected whenever the air cleaner air
temperature is above the calibrated value of the TES
and the WOT switch has been engaged.
When the Open Loop 2 mode is selected, the stepper
motor is driven to a calibrated number of steps rich of
initialization and the air control valve routes air down
stream. However, if the "lean limit" (altitude) jumper
wire is installed, the air is instead routed upstream. The
WOT timer is activated whenever OL2 is selected and it
remains active for a preset period of time. The WOT
timer remains inoperative if the "lean limit" (altitude)
jumper wire is installed.
• Open Loop 4
Open Loop 4 is selected whenever manifold vacuum
falls below a predetermined level. During OL4 oper
ation, the stepper motor is positioned at the in
itialization position. Air injection is switched upstream
during OL4 operation. However, air is diverted down
stream if the extended OL4 timer is activated and if the
FUEL SYSTEMS 1J-111
"lean limit" (altitude) jumper wire is not installed. Air is
also diverted downstream if the WOT timer is activated.
• Open Loop 3
Open Loop 3 is selected when the ignition advance
vacuum level falls below a predetermined level.
When the OL3 mode is selected, the engine rpm is also
determined. If the rpm (tach) voltage is greater than the
calibrated value, an engine deceleration condition is as
sumed to exist. If the rpm (tach) voltage is less than the
calibrated value, an engine idle speed condition is as
sumed to exist.
• Open Loop 1
Open Loop 1 will be selected if the air cleaner air
temperature is above a calibrated value and Open Loop
2,3 or 4 is not selected, and if the engine coolant temper
ature is below the calibrated value.
The OL1 mode operates in lieu of normal closed-loop
operation during a cold engine operating condition. If
OL1 operation is selected, one of two predetermined
stepper motor positions are chosen, dependent on
whether or not the altitude circuit (lean limit) jumper
wire is installed.
With each engine start-up, a start-up timer is acti
vated. During this interval, if the engine operating con
dition would otherwise trigger normal closed loop
operation, OL1 operation is selected.
• Closed Loop
Closed loop operation is selected after either 0L1,
OL2, OL3 or OL4 modes have been selected and the
start-up timer has timed out. Air injection is routed
downstream during closed loop operation. The pre
determined lean mixture ceiling is selected for a preset
length of time at the onset of closed loop operation.
Open Loop Operation Predetermined Position Variation
An additional function of the MCU is to correct for a
change in ambient conditions (e.g., high altitude). Dur
ing closed loop operation the MCU stores the number of
steps and direction that the metering pins aredriven to
correct the oxygen content of the exhaust. If the move
ments are consistently to the same position, the MCU
will vary all open loop operation predetermined meter
ing pin positions a corresponding amount. This function
allows the open loop air/fuel mixture ratios to be "tai
lored" to the existing ambient condition during each
uninterrupted use of the system. This optimizes emis
sion control and engine performance for the ambient
operating condition involved.
dosed Loop Operation
The CEC system controls the air/fuel ratio with mov
able air metering pins, visible from the top of the carbu
retor air horn, that are driven by the stepper motor. The
stepper motor moves the metering pins in increments or
small steps via electrical impulses generated by the
MCU. The MCU causes the stepper motor to drive the