Renix 2.5 EGR Valve Operation (and testing)

[jamcomanche]

I made a post recently looking for a good source for replacement EGR Valves for my 87 2.5 - I was under the impression that these valves could be tested simply by applying vacuum to the connection on the valve to check for leaks and proper valve function.    
After returning a few valves that wouldnt hold vacuum, I contacted Standard Motor Products (one of the manufacturers of replacements for the OEM 53002483 valves) and felt pretty dumb after I got some clarification on the specifications.  

Renix 2.5 EGR Valve (86-90) 
OEM Part #: 53002483
Replacement/Interchange Part #: EGV580
Type: Positive Backpressure Valve

Operation
A positive backpressure EGR valve is a vacuum-operated emission control device that uses exhaust pressure to modulate exhaust gas recirculation. It remains closed at idle, opening only when engine load increases. This design prevents engine hesitation and stalling by ensuring EGR doesn't occur during low-load operations.
 

 - Low Backpressure (Idle/Deceleration): At idle, exhaust backpressure is low. The internal bleed valve opens, bleeding off any engine vacuum that is applied to the main valve. Because the vacuum escapes, the EGR valve stays closed.
 - High Backpressure (Acceleration/Load): When you press the gas pedal, exhaust backpressure increases. This force pushes the pilot valve closed, sealing the vacuum bleed port. As the vacuum builds and holds, it overcomes the main control spring, pulling the EGR diaphragm up and allowing exhaust gases to recirculate into the intake manifold.

 

Testing

1. Set parking brake, place M/T in neutral, A/T in park.
2. Start and warm engine to normal operating temperature; increase idle to, and hold at, 2500 to 3000 RPM.
3. Disconnect vacuum hose at EGR valve. Check for at least 5"-8" of vacuum at this point. If no vacuum, check source including all hoses and vacuum controls (e.g. ported vacuum switches, control solenoids)
4. To check EGR operation, bypass EGR solenoid (when used) with appropriate tubing. Using thumb, disconnect and plug vacuum hose at EGR valve. When removed, look for downward movement of diaphragm (can be seen through housing openings) and listen for a slight increase in engine speed.
5. Reconnect vacuum hose. Diaphragm should move upward and engine speed should decrease slightly.
6. When engine speed change and diaphragm movement occur with vacuum hose removed or installed, EGR is operating properly. If EGR solenoid is used, remove bypass tubing and reconnect.
    

NOTE: Use only the instructions listed above to test the replacement valve. Due to its design, an off-car, bench test cannot be performed with a hand-held vacuum pump.