Backpressure EGR Valve

Check vacuum hose routing. Ensure carburetor vacuum port is not plugged. Warm engine to operating temperature. Increase engine speed to 1500-2500 RPM. Ensure EGR valve opens (valve opens slowly on some models). With engine at idle, connect intake manifold vacuum to EGR valve. Engine should run rough or stall. If EGR valve does not open, check for faulty backpressure sensor or EGR valve. If EGR valve opens, but engine RPM does not change, check for clogged EGR passages.