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.
Thermal Vacuum Switch
EGR Thermal Vacuum Delay Switch should be open above 100°F coolant temperature, permitting ported vacuum signal to reach EGR valve above that temperature. Check as follows: Remove EGR valve vacuum hose at EGR valve and connect hose to a vacuum gauge. Start engine, place transmission in Neutral and open throttle partially. As throttle is opened, vacuum gauge should respond with an increase in vacuum reading.
If operation is satisfactory, remove gauge and reconnect hose to EGR valve. If gauge does not respond to throttle opening, remove carb-to-switch hose from switch and connect to vacuum gauge. If vacuum gauge responds to throttle opening, then replace with new switch. If gauge does not respond to throttle opening, then check for plugged hose or defective carburetor.
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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.