Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 96

IGNITION CIRCUITRY
ESA - Ignition Circuitr y
The operation of the ignition system in TCCS is The types of ignition system in TCCS can be dif-
basically the same as the operation of the ferentiated by the method used to distribute cur-
ignition system in conventional EFI, except that rent to the spark plugs : either the conventional
the igniter in the latter is turned on and off
type, in which a distributor is used, or DLI
directly by the signal generator .
( distributorless ignition) and DIS (direct ignitio n
Signal
generator
Distributo r
Ignition
Igniter coi l
CONVENTIONAL EFI
Spark
plug s
OHP 6 2
In the TCCS, the signals from the signal
generator first pass through the ECU befor e
going to the igniter .
Signal Spark
generator Distributor plug s
Ignition , .
I
Igniter coi l
~
~
_Vv
IGT
TCC S
ECU
OHP 62
system), in which no distributor is used .
In this section, we will explain the operation of
both the conventional ignition system used in
TCCS, and the DLI and DIS . For an explanation of
the operation of the ignition system for the con-
ventional EFI, refer to Step 2, vol .3 (Ignition
System) .
REFERENCE
An igniter is included in the Engine ECU of the
4A-FE engine made by Bosch .
1 . CONVENTIONAL IGNITION CIRCUITRY FOR TCC S
The microprocessor in the ECU determines the
ignition timing based on the G(G1 and G2) and
NE signals, as well as on signals from each
sensor . After determining the ignition timing,
the ECU sends an IGT signal to the igniter .
When the IGT signal goes off, transistor Tr2 in
the igniter goes off . As a result, the primary
current to the ignition coil is interrupted, causing
a high voltage (of approx . 20 to 35 kV) to be
generated by the secondary coil in the ignition
coil . This in turn causes sparks to be generated
by the spark plugs .
The igniter incorporates the following circuitry in
order to deliver a stable secondary voltage and
assure system reliability :