See Figure 1
This valve is found between the right hand exhaust manifold and the exhaust pipe on California V6 diesel cars. The EPR valve is used in the exhaust flow to increase back pressure in the exhaust system, thus increasing exhaust flow through the EGR system. The valve operates from the same vacuum source as the EGR valve. It should be fully closed at idle, and will open as the throttle is opened.
TESTING THE EPR VALVE
To test the EPR valve, apply vacuum to the vacuum port on the valve. The valve should be fully closed at 12 in. Hg of vacuum, and open below 6 in. Hg. of vacuum.