Run Mode C2-2 - Pontiac Fiero 1988 Service Manual

6E3-C2-2 DRIVEABILITY AND EMISSIONS - FUEL INJECTION (PORT)
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C O L D S T A R T V A L V E
flT] V A L V E O - R I N G S E A L
[T] T U B E 0 - R I N G S E A L
1/15/87
8 P 0 9 4 3 - A S
Figure C2-2 - Cold Start Valve Assembly
This ranges from 1.5:1 at - 3 6 ° C (-33°F ) to 14.7:1 at
9 4 ° C ( 201°F) running temperature.
The electronic control module (ECM) controls the
amount of fuel delivered in the Starting Mode by
changing how long the injectors are turned "ON" and
"OFF." This is done by "pulsing" the injectors for very
short times and is referred to as injector pulse width.
The cold start valve (Figure C2-2), not controlled
by the ECM, is used to provide additional fuel during
the starting mode to improve cold start-ups. This
circuit is important when engine coolant temperature
is very low because the other six injectors would not be
pulsed "ON" long enough to provide the needed
amount of fuel to start. The cold start valve is
different from the other injectors in that it causes the
fuel to be vaporized for a better combustible mixture.
This circuit is activated only in the crank mode.
The power is supplied directly from the starter
solenoid and only "ON" in the crank mode. The
system is controlled by a cold start fuel injection
switch which provides a ground path for the valve
during cranking whenever engine coolant is below
35°C(95°F).
The cold start fuel injection switch (see Figure
C2-3) consists of a bimetal material which opens the
circuit at specified coolant temperature. This bimetal
is also heated by the winding in the switch which
allows the cold start valve to stay "ON" 8 seconds at
- 2 0 ° C (-4° F) or below. Above (-20°C), the maximum
time the switch stays closed is proportional to the
coolant temperature. In other words, as the coolant
temperature goes up the maximum cold start valve
"ON" time goes down.
C l e a r Flood Mode
If the engine floods, clear it by pushing the
accelerator pedal down all the way. The ECM then
pulses the injectors at an air/fuel ratio of 20:1.
[T1
COLD START FUEL
INJECTION SWITCH
P H COOLING FAN SWITCH
6S 2542-6E
Figure C2-3 - Cold Start Fuel Injection Switch
The ECM holds this injector rate as long as the
throttle stays wide open, and the engine rpm is below
400. If the throttle position becomes less than 80%,
the ECM returns to the Starting Mode.
Run Mode
The Run Mode has two conditions called "Open
Loop" and "Closed Loop."
When the engine is first started, and rpm is above
400 rpm, the system goes into "Open Loop" operation.
In "Open Loop," the ECM will ignore the signal from
the oxygen (O2) sensor, and calculate the air/fuel ratio
based on inputs from the coolant temperature and
MAP sensors.
The system stays in "Open Loop" until the
following conditions are met:
1. The O2 sensor has varying voltage output,
showing that it is hot enough to operate properly.
(This depends on temperature.)
2. The coolant sensor is above a specified
temperature.
3. A specific amount of time has elapsed after
starting the engine.
The specific values for the above conditions vary
with different engines, and are stored in the
programmable read only memory (PROM). When
these conditions are met, the system goes into "Closed
Loop" operation. In "Closed Loop," the ECM
calculates the air/fuel ratio (injector on-time) based on
the signal from the O2 sensor. This allows the air/fuel
ratio to stay very close to 14.7:1 .
Acceleration Mode
The ECM looks at rapid changes in throttle
position and manifold pressure (vacuum) and
provides extra fuel.