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 MANUALSGMC1991JIMMY 5.7 K, AUTOMATIC, 4L60/MD8REPAIR AND DIAGNOSIS (SINGLE PAGE)TRANSMISSIONAUTOMATIC TRANSSERVICING - A/TADJUSTMENTSVACUUM REGULATOR VALVE (VRV)DIESEL
1991 GMC Jimmy 5.7 K, Automatic, 4L60/MD8
Vacuum Regulator Valve (VRV): Diesel
1991 GMC Jimmy 5.7 K, Automatic, 4L60/MD8SECTION Diesel
- Loosen vacuum regulator valve-to-injection pump bolts enough to allow for regulator valve rotation. Attach vacuum pump to bottom vacuum port of valve (vacuum gauge to top port). See Fig 1.
- Insert .646" (16.4 mm) Gauge Block (J-33043) between gauge boss on injection pump and wide open stop screw on throttle lever. Rotate throttle shaft against block.
- Apply 18-21 in. Hg vacuum to VRV. Slowly rotate VRV body clockwise (facing valve) until vacuum gauge reads 10.9-12.1 in. Hg. Hold valve body in this position and tighten mounting screws.NOTE: Set valve while rotating in a CLOCKWISE direction only.
- Check adjustment by allowing throttle shaft to return to idle position, then rotate shaft back against gauge block. If vacuum gauge reading is not 10.9-12.1 in. Hg, readjust valve.
- With vacuum regulator valve vacuum set, confirm detent switch point by reading resistance between ignition terminal and detent terminal. Attach an ohmmeter across ignition terminal (Pink/Black wire) and detent terminal (Orange wire).
- Insert Gauge Bar (J-36142) between gauge boss on pump and wide open stop screw on throttle shaft. See Fig 1. Rotate and hold throttle lever against gauge bar. There should be no continuity (infinite resistance).
- Release throttle lever and allow it to return to idle position. Remove gauge bar. Rotate throttle lever to Wide Open Throttle (WOT) position. Check switch for continuity. There should be continuity before throttle reaches WOT position. If switch does not meet specification, return to step 1).
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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.