Egr question
Race Director
Joined: Mar 2015
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Does this help?
There were distinct differences in the way GM handled control of the EGR valve. Additionally, they used two different ways to determine if the exhaust gas flowed. All C4s used electric solenoids, some NO (normally open) or NC (normally closed) until current was supplied. Some used manifold vacuum like the 1984 and 1992-1996 Corvette opening the EGR valve with a NC solenoid. The 1985-1989 Corvettes used ported vacuum supplying vacuum once the throttle was opened through a NO vacuum control valve solenoid. The ECM controlled either the NO or NC solenoid which has ignition power as long as the engine is running. The ECM supplied the ground to control the solenoid and vacuum flow to the EGR valve. Certain criteria had to be met; engine at operating temperature, light to moderate throttle opening, and under steady state cruising.
There were distinct differences in the way GM handled control of the EGR valve. Additionally, they used two different ways to determine if the exhaust gas flowed. All C4s used electric solenoids, some NO (normally open) or NC (normally closed) until current was supplied. Some used manifold vacuum like the 1984 and 1992-1996 Corvette opening the EGR valve with a NC solenoid. The 1985-1989 Corvettes used ported vacuum supplying vacuum once the throttle was opened through a NO vacuum control valve solenoid. The ECM controlled either the NO or NC solenoid which has ignition power as long as the engine is running. The ECM supplied the ground to control the solenoid and vacuum flow to the EGR valve. Certain criteria had to be met; engine at operating temperature, light to moderate throttle opening, and under steady state cruising.
