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
Vacuum signal is supplied to EGR valve from a port upstream from throttle valve. When intake manifold temperature is below 86°F (30°C), vacuum signal is modulated through the orifice by an air bleed to the air cleaner (on EGR control valve orifice equipped models). Additionally, with intake manifold wall temperatures between 86°F (30°C) and 104°F (40°C), vacuum signal is further modulated through the thermo vacuum switch.
For Federal 2WD models, the vacuum signal is also modulated with atmospheric pressure through a solenoid valve that has its air flow regulated by the electronic control module. See AIR INJECTION article.
When EGR valve is open, exhaust gases flow through EGR valve and pipe and into the intake manifold. The strength of vacuum signal at EGR valve determines how much exhaust gas is recirculated.
| Application (1) | Specification: In. (mm) | |||||
|---|---|---|---|---|---|---|
| Calif. | ||||||
| Manual Trans. | ||||||
| 2WD | .028 (.70) | |||||
| Federal | ||||||
| Manual Trans. | ||||||
| 2WD | ||||||
| Hitachi | .028 (.70) | |||||
| Carter | .031 (.80) | |||||
| 4WD | .020 (.50) | |||||
| 4WD (High Altitude) | .039 (1.0) | |||||
| Auto. Trans. | ||||||
| 2WD | .020 (.50) | |||||
| 4WD (High Altitude) | .028 (.70) | |||||
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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.