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.
1990 Ford Bronco II RWD, Standard, M5OD-R1FACTORY OEM SERVICE PROCEDURE
Air Check Valve
- Visually inspect thermactor hoses, tubes, control valve(s) and check valve(s) for leaks from exhaust gas backflow. If holes are found and/or traces of exhaust gas products are evident, check valve may be suspect.
- Valve should allow free flow of air in direction of arrow only. See Fig 1 . The valve(s) should check (or block) free flow of exhaust gas air in opposite direction.
- If air does not flow as indicated or if exhaust gas backflows opposite of direction of arrow in illustration, replace check valve.
Factory Service Tools
Use the Manual With the Right Hardware
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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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