DESCRIPTION
A Throttle Closer (TC) system is used on 1500 HF models with manual transmission. Throttle closer system closes throttle valve below its idle position when vehicle is decelerated under certain conditions. System consists of a control unit, clutch switch, speed sensor, vacuum switch, throttle control solenoid valve and throttle controller.
OPERATION
When engine speed and vehicle speed are above a certain minimum, and clutch pedal is not depressed, vacuum is available to throttle controller diaphragm through throttle control solenoid valve. This retracts the throttle stop screw closing the throttle completely. A minimum amount of fuel required to keep engine running is drawn from slow speed fuel system.
CLUTCH SWITCH
- Back probe positive voltmeter lead into Blue wire terminal of control unit connector. Connect negative voltmeter lead to ground. Turn ignition on and depress clutch pedal. Check for voltage.
- If there is no voltage, adjust or replace clutch switch as necessary and retest. If there is voltage, release clutch pedal and check for voltage. If there is no voltage, clutch switch is okay. If there is voltage, check clutch switch adjustment and retest.
SPEED SENSOR
- Raise and support front of vehicle. Set parking brake and block rear wheels. Connect voltmeter positive lead or test light to Yellow/Black wire at control box connector. Connect negative lead to ground.
- Start engine. Shift transmission into 2nd gear and accelerate slowly, while observing voltmeter. Voltmeter should read battery voltage below 6 MPH and no voltage above 12 MPH.
- If voltmeter readings are not as specified, install new speed sensor and retest. If there is no voltage during speed sensor test, check for bad connection, faulty wiring or fuse, or defective speed sensor. Repair or replace as necessary.
VACUUM SWITCH B
Disconnect vacuum hose at vacuum switch B and connect vacuum pump to switch. Apply vacuum and check for voltage at vacuum switch. Voltage should be available under conditions shown in VACUUM SWITCH VOLTAGE table.
| Application | Vacuum Hose | Wire Color | (1) Voltage Available |
|---|---|---|---|
| Fed. | 1 | Brn | Above 6 in. Hg |
| Fed. | 1 | Brn/Blk | Below 6 in. Hg |
| Calif. | 12 | Brn | Above 7.9 in. Hg |
| High Alt. | 12 | Brn | Above 4 in. Hg |
| (1) Vehicle speed above 10 MPH. | |||
| (1) | Vehicle speed above 10 MPH. |
VACUUM SWITCH B VOLTAGE
SYSTEM CHECK
- Disconnect vacuum hose No. 22 from outer fitting of throttle controller. Raise and support front of vehicle. Set parking brake and block rear wheels. Shift transmission into 2nd gear and check for vacuum with vehicle speed above 10 MPH and engine speed above 800 RPM. There should be vacuum.
- If there is vacuum, proceed to step 7). If there is no vacuum, check for voltage at throttle control solenoid valve (Black/White wire) with vehicle speed above 10 MPH and engine speed above 800 RPM. If voltage is not present, check speed sensor, vacuum switch B and clutch switch.
- Check for voltage at Blue wire between control unit and ignition coil with ignition on. If there is no voltage, check wiring between control unit and ignition coil.
- Check for voltage at Black/Yellow wire terminal of control unit connector with ignition on. If no voltage is present, check wiring and fuse. Ensure Black wire between control unit and ground has continuity.
- If voltage is present, disconnect vacuum hose No. 12 from throttle control solenoid valve and check for vacuum. If there is vacuum, replace throttle control solenoid valve and retest.
- If there is no vacuum, check vacuum hose to throttle control solenoid valve for disconnected hose, leaks or blockage. Check carburetor port for blockage. Clean and repair as necessary.
- Connect hand vacuum pump to outer fitting of throttle controller. Apply 20 in. Hg of vacuum with engine idling. If engine stops, test is complete. If engine does not stop, ensure throttle controller linkage moves freely and throttle cable is properly adjusted. If okay, replace throttle controller and retest.
