Test 1: 4.2L

With engine not running, disconnect vacuum hose from EGR valve. Connect a hand-held vacuum pump to EGR valve. Apply vacuum to EGR valve and ensure that diaphragm will hold vacuum until released. EGR valve should close when vacuum is released. Start engine. Disconnect vacuum hose to EGR valve and plug. Apply vacuum to EGR valve. Engine should run rough or stall. If system operates as indicated, system is functioning properly.