Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 89

EFI - Functions of Engine EC U
-RELEVANT SIGNALS
• Throttle position (IDL)
• Engine speed (NE )
• Coolant temperature (THW)
• Stop lamp switch (STP )
- REFERENC E
1 . In some manual transmission models, the
clutch switch (N/C) signal is also used as a
condition for fuel cut-off .
2 . There are some models in which the fuel
will be cut off when the injection volume
during deceleration falls below the predeter-
mined level even if the throttle valve is not
completely closed (idle contact off) .
i
b . Fuel Cut-Off at High Engine Speed s
To prevent engine over-run, fuel injection is
halted if the engine speed rises above a
predetermined level . Fuel injection is resumed
when the engine speed falls below this level .
RELEVANT SIGNA L
• Engine speed (NE )
c . Fuel Cut-Off at High Vehicle Speed s
In some vehicles, fuel injection is halted if the
vehicle's speed exceeds a predetermined level .
Fuel injection resumes after the speed drops
below a predetermined level .
- RELEVANT SIGNAL
• Vehicle speed (SPD )
IYV I C
The Engine ECU also performs various other
corrections in addition to these (page 72 to
79) .
3 Voltage correctio n
There is a slight delay between the time that the
Engine ECU sends an injection signal to the
injectors and the time that the injectors actually
open . This delay becomes longer the more the
voltage of the battery drops . This means that
the length of time that the injector valves
remain open would become shorter than that
calculated by the ECU, causing the actual air-
fuel ratio to become higher (i .e ., leaner) than
that required by the engine, if this were not
prevented by voltage correction .
In voltage correction, the ECU compensates for
this delay by lengthening the duration of the
injection signal by a period corresponding to the
length of the delay . This corrects the actual
injection period so that it corresponds with that
calculated by the ECU . (The amount of this
correction value depends on the engine model . )
Voltage correctio n
Off
Ope n
Closed
Injector
actually open
OHP
68
0
I
----------------------------
Standard
operating
delay tim e
Low
-
14
-
High
Ba
tt
e
ry
voltage (V)
OHP 58
RELEVANT SIGNA L
• Ba
tt
e
ry
voltage (+B)
Injection
signa l
~
79