TPS ADJUSTMENT (GASOLINE)
Note. On all models except 2.8L engine (VIN R), Throttle Position Sensor (TPS) is NOT adjustable. Resistance values given in table are for reference only. If resistance value is not as specified, replace TPS. For testing procedures, refer to appropriate SELF-DIAGNOSTICS or SYSTEMS & COMPONENTS TESTING article.
TPS ADJUSTMENT (DIESEL)
- Loosen Throttle Position Sensor (TPS) retaining screws. If TPS is being replaced, install new TPS on injection pump and lightly tighten screws. Make jumper wires using the following General Motors' parts: Terminals No. 1214836 and 12014837. Install jumper wires between TPS and harness.
- Turn ignition on, but DO NOT start engine. Install .646" (16.41 mm) thick Gauge Block (J-33043-2) between gauge boss on injection pump and wide open throttle valve stop screw on throttle lever (switch on position).
- Rotate throttle shaft and hold the wide open throttle stop screw against gauge block. Using a DVOM, measure reference voltage across terminals "A" (Black wire) and "C" (Gray wire). Record voltage reading. Now measure and record TPS return voltage between terminals "B" (Dark Blue wire) and "C" (Gray wire).
- Divide TPS return voltage by the reference voltage. For example: a TPS return voltage of 3.15 volts divided by a 5.01 reference voltage equals a .63 TPS voltage ratio. Refer to the «TPS ADJUSTMENT SPECIFICATIONS»(ref-10145-S12952670662001010200000) table. The TPS voltage ratio uncertainty should be within ±.03 volts.
- To adjust TPS, loosen attaching screws and rotate TPS until a correct TPS voltage ratio is obtained. Tighten attaching screws to 53 INCH lbs. (6 N.m).
- Release throttle lever and allow it to return to the idle stop position. Check TPS voltage between terminals "B" (Dark Blue wire) and "C" (Gray wire). Now return lever against gauge block and note voltage reading.
- Voltage should be less than 2.2 volts at closed throttle and return to within ±.03 volts of the adjusted voltage when throttle is against gauge block.
- If reading does not return to adjusted voltage, repeat adjustment procedure. If reading is still incorrect or if voltage is not less than 2.2 volts with throttle closed, replace TPS.
- After TPS adjustment, remove gauge block. Turn ignition off. Remove jumper wires and reconnect TPS harness connector. Install air cleaner assembly and related hoses.
| Application | TPS Voltage Ratio |
|---|---|
| Automatic Transmission | .63 |
| Manual Transmission | .63 |
TPS ADJUSTMENT SPECIFICATIONS
VACUUM REGULATOR VALVE/DETENT SWITCH ADJUSTMENT (DIESEL)
- Loosen vacuum regulator valve so it is free to rotate on pump. Attach a hand-held vacuum pump and apply 20 in. Hg. to bottom port of valve. Attach vacuum gauge to top port of valve.
- Insert 0.646" Gauge Block (J-33043-A) between gauge boss on injection pump and wide open stop screw on throttle lever (switch on position). (Scheme 1) NOTE: Always refer to Emission Control Label for correct gauge block size.
- Rotate and hold throttle shaft against gauge block. Slowly rotate vacuum regulator valve body clockwise (facing valve) until vacuum gauge reads 10.9-12.1 in. Hg. Hold valve body at this position and tighten mounting screws.
- Check adjustment by allowing throttle shaft to return to idle stop position. Then rotate throttle shaft back against gauge block. Vacuum gauge reading must be between 10.9-12.1 in. Hg. If vacuum is outside limits, reset valve.
- With vacuum valve set, confirm detent switch point by reading resistance between ignition (Pink/Black wire) and detent terminal (Orange wire). Insert Switch Gauge (J-36142) between wide open stop pin and wide open stop screw on throttle lever. (Scheme 1)
- Rotate throttle lever against switch gauge. Continuity should NOT be present. Release throttle lever and remove gauge. Rotate throttle lever to wide open throttle (lever stop screw touching pump stop pin).
- Check switch for continuity. Switch must have 0-1 ohm resistance before throttle reaches wide open position. If switch does not meet specifications, reset assembly by returning to step 1) and repeating entire procedure.
