I did a little more digging and I am going to try to compile all of my research in one place.
First, I reviewed the 1992 cruise control EWD that DivByZero posted in his thread linked above. The nice thing about this cruise control (CC) diagram is that it shows
both 1HZ/1HDT wiring AND 1FZ-FE wiring.
It may be difficult to see, but you can click on the photo to enlarge.
The
YELLOW input into the CC ECU is "N & C". Presumably "Neutral" or "Clutch" switch for CC cancel feature (i.e. For manual trans, "When you push the clutch in, the CC cancels." Or for auto trans, "CC will not engage unless you are in Drive.").
The
RED input into CC ECU is "IDL" input from the TPS (idle circuit).
The
GREEN input into CC ECU is "OD" input from auto transmission (overdrive).
And the
BLUE input into CC ECU is "ECT" input from auto transmission (ECT Power).
You will also notice, for IDL, OD, and ECT circuits, they are only included on the 1FZ-FE models ("1FZ-FE" in parenthesis on those circuits). So we can presume that the 1HZ and 1HD-T versions did not have those inputs for this YM.
If we look further into the IDL circuit signal from the TPS, we can make more conclusions. Below is the TPS inspection diagram from the 1996 FZJ80 EWD.
The TPS on an FZJ80 is a 4-wire type. Meaning that it has both Throttle Position and Idle circuits. The 4 pins are voltage-in (VC), throttle position signal-out (VTA), ground (E2), and idle circuit (IDL). The idle circuit is simply ON or OFF. When the throttle butterfly is in the closed position, the idle circuit is closed and 12 volts is transmitting through the idle circuit. When the throttle butterfly is in open position, the idle circuit is also open and is transmitting 0 volts through the idle circuit (Resistance = Infinity).
This also means that no signal is being sent to the CC ECU from the IDL circuit when the throttle is open.
I suspect all of the idle (IDL) and transmission (OD and ECT) inputs into the CC ECU are related to transmission lockup and overdrive features and are helping the CC system regulate the transmission to maintain speed and prevent engine stall.
From the repair manual regarding TCM:
FUNCTION OF TCM
• Control of Shift Timing
The TCM has programmed into its memory the optimum shift pattern for each shift lever position
(D, 2, L positions) and driving mode (Normal or Power).
Based on the appropriate shift pattern, the TCM turns No.1, No.2 and timing solenoid valves on
or off in accordance with the vehicle speed signal from the vehicle speed sensor and the throttle
opening signal from the throttle position sensor. In this manner, the TCM operates each shift
valve, opening or closing the fluid passages to the clutches and brakes to permit up−shift or
down−shift of the transmission.
HINT: The electronic control system provides shift timing and lock−up control only while the
vehicle is traveling forward. In REVERSE, and NEUTRAL, the transmission is mechanically, not
electronically controlled.
• Control of Overdrive
Driving in overdrive is possible if the O/D main switch is on and the shift lever is in the D position.
However, when the vehicle is being driven using the cruise control system (CCS), if the actual
vehicle speed drops to about 4 km/h (2mph) below the set speed while the vehicle is running in
overdrive, the CCS ECU sends a signal to the TCM to release the overdrive and prevent the
transmission from shifting back into overdrive until the actual vehicle speed reaches the speed
set in the CCS memory.
On this model, if the coolant temperature falls below 55* C (131 F), the ECM sends a signal to the
TCM, preventing the transmission from up−shifting into overdrive.
Control of Lock−Up System
The TCM has programmed in its memory a lock−up clutch operation pattern for each driving
mode (Normal or Power). Based on this lock−up pattern, the TCM turns lock−up solenoid valve
on or off in accordance with the vehicle speed signals received from the vehicle speed sensor and
the throttle opening signals from the throttle position sensor.
Depending on whether lock−up solenoid valve is on or off, the lock−up relay valve performs
changeover of the fluid passages for the converter pressure acting on the torque converter clutch
to engage or disengage the lock−up clutch.
Mandatory Cancellation of Lock−Up System:
If any of the following conditions exist, the TCM turns off lock−up solenoid valve to disengage
the lock−up clutch.
(1) The brake light switch comes on (during braking).
(2) The IDL points of the throttle position sensor close (throttle valve fully closed.).
(3) The vehicle speed drops 4 km/h (2mph) or more below the set speed while the cruise control
system is operating.
(4) The coolant temperature falls below 70C (158F).
The purpose of (1) and (2) above is to prevent the engine from stalling if the rear wheels lock up.
The purpose of (3) is to cause the torque converter clutch to operate to obtain torque multiplica−
tion. The purpose of (4) is both to improve general driveability, and to speed up engine warm −up.
Also, while the lock−up system is in operation, the TCM will temporarily turn it off during up−
shift or down−shift in order to decrease shifting shock."
So basically, I think you can abandon the IDL, OD, and ECT circuits on the CC ECU when performing a 1HZ, 1HDT, or 1HDFT swap with manual trans.
You will still need to wire the
YELLOW neutral safety switch to your clutch pedal (
or de-pin it completely) to trick 1FZ CC into thinking the truck is in Drive. For clutch cancel, some wiring trickery will need to be performed since the neutral safety switch cancels cruise when powered. Probably by utilizing a Normally Open type relay.
I hope this helps someone performing a swap.
Please let me know if you see any errors.
