Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1990HI-CUBE 7.4 N, 400/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCEENGINE CONTROLS - ADJUSTMENTSTPS ADJUSTMENT (DIESEL)
1990 Chevrolet Hi-Cube 7.4 N, 400/M40
TPS Adjustment (Diesel)
1990 Chevrolet Hi-Cube 7.4 N, 400/M40SECTION 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 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.
TPS ADJUSTMENT SPECIFICATIONS
| Application | TPS Voltage Ratio |
|---|---|
| Automatic Transmission | .63 |
| Manual Transmission | .63 |
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.