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.
EGR System: Operation
EGR valve receives operating vacuum from carburetor ported vacuum (throttle body ported vacuum for fuel injected models). A thermo vacuum valve, used on all carbureted models, bleeds off vacuum to EGR valve when intake manifold wall temperature is below 86°F (30°C). When intake manifold wall temperature reaches 104°F (40°C), vacuum bleed off stops and normal EGR operation begins.
To restrict vacuum bleed off, an EGR leak orifice, which is placed within bleed off line, is used. This vacuum bleed off system is used on all carbureted models except for auto. trans. equipped federal models.
On all fuel injected models, EGR operating vacuum is controlled by the ECU and the EGR solenoid valve. This system does not allow EGR operation until engine reaches normal operating temperature or at wide open throttle. On turbo equipped models, EGR operation is cancelled during turbo boost conditions.
| Application | Specification: In. (mm) | ||
|---|---|---|---|
| Calif. | |||
| Auto. Trans. | |||
| 2WD | .028 (0.7) | ||
| 4WD | .031 (0.8) | ||
| Manual Trans. | .031 (0.8) | ||
| Federal | |||
| Manual Trans. 2WD & 4WD | .020 (0.5) | ||
| High Altitude Man. & Auto. Trans | .039 (1.0) | ||
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.