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.
1988 Chevrolet Hi-Cube 5.7 M, 475/M40FACTORY OEM SERVICE PROCEDURE
System Testing
- With engine cold, position transmission in "N" or "P" and apply parking brake. Start engine and observe movement of actuator rod and exhaust heat valve. Valve should move to closed position.
- If valve does not close, disconnect hose from actuator and apply 10 in. Hg vacuum to actuator. Valve should close and stay closed. If valve does not stay closed, replace actuator. Check valve rod and valve for proper operation. Repair as necessary.
- When engine temperature reaches 105°F (40°C), exhaust heat valve should move to open position.
- If valve does not open, disconnect hose at actuator and check for vacuum. If there is vacuum, replace TVS. If no vacuum is present, replace actuator.
Factory Service Tools
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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.
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