This is the original 3T-GTEU EFI, completely analog, manufactured by
Nippondenso, based on the Bosch L-Jetronic.
The control unit is mounted behind the blower duct, above passenger's
feet. The knock control unit should also be around there, in my case
it's on the right side of passenger's feet.
Air flow sensor
this sensor is of the flap-type.
It measures the air entering the engine (assuming no intake leaks).
When the flap is totally closed, meaning no air is entering the engine,
fuel pump is not running. This is achieved by a switch connected to the
flap, which connects the fuel pump ground (connector FC) to chassis ground
(E1) only when it is open at least partially.
Air temperature sensor is the third function the whole air flow meter
serves, this is a standard automotive NTC resistor (connector THA).
Here's the resistance curve:
Coolant temperature sensor
This is identical to the air temperature sensor described above,
except that it measures the coolant temperature below the waterneck.
Idle speed and fuel cut-out/cut-in during deceleration depend on this sensor
Grounds the cold-start injector for 5-12 seconds after starting.
The throttle switches are mounted on the throttle plate axle, and
in this case only have three possible outputs, idle (connector IDL),
wide open throttle (connector PSW) or neither. Connector TL provides
the voltage which the switches deliver to IDL or PSW when closed.
The EFI itself uses 2 pressure switches. First one is used for
enrichment (connector PE) above 0.15 bar (2.2psi) of boost.
This pressure switch measures the pressure through a vacuum line (ok, ok,
it's not in this case always under vacuum) from the intake manifold.
The second pressure switch is for fuel cutoff (connector PC) above
0.5 bar (7.3psi) of boost. This one is measured before the throttle
body. There are two reasons why this does not seem to be a good idea
to keep functioning: the fuel cutoff is not complete, it will
lead to a very lean condition under high load and is BAAAAD for the
engine. It had not caused any damage, but it did render high-speed
drivability to unbearable.
Oxygen sensor & sub-oxygen sensor
Oxygen sensor is used to keep the air-fuel mixture at 14.7:1 (lambda=1)
under "normal" driving conditions, in this case intake manifold vacuum
has to be over 0.3 bar, engine fully warmed up (Coolant sensor THW) and
the fuel cut-out and idle must not be active. That is, it's only used
when cruising with only moderate acceleration or deceleration takes place.
The connector for oxygen sensor is OX. The sub-oxygen sensor (connector OT)
would be mounted after a catalytic converter, but I have neither.
Vehicle speed limiter sensor
Limits the vehicle speed to 180km/h, this is obligatory in Japanese market
vehicles. Guess is this still connected ;)
Connector VMAX. Just clipping the (originally pink, but check the connector
picture) wire will disable it, if you even have the sensor mounted.
Air conditioner relay
I don't have air conditioning so it's not used. It would either shut
down the A/C at idle or raise idle speed when A/C is on. Connector A/C.