Questions and Answers

Blazer EGR Valve Q. Vincent, I have a 1995 Blazer with a, V-6, Multi-port injection, 4 wheel drive, and automatic transmission. The problem I have is recently when first started, and in "open-loop" (I have a scan tool), the car runs poorly. Rough idle black smoke etc.

As soon as it goes into "closed-loop" it runs perfectly. It has new plugs, wires, and I have tried a new O2 sensor. The only problem the vehicle has had is on a long uphill run the "service engine soon" light has come on, the error set is an EGR pintle position error. After a while the light goes out. It has done this since it was new. Any help or direction would be appreciated.

A. Your truck has, what GM calls, A Linear Exhaust Gas Recirculation Valve. In most EGR designs, the flow is "Open Loop," in which the system has no feedback mechanism to monitor actual flow and then to correct it. The linear EGR valve is unique in that the control module continuously monitors pintle height and continuously corrects it in order to obtain accurate flow, making linear EGR a "Closed Loop" system.

When the solenoid is de-energized (control module breaks the circuit), the pintle is sealed against the orifice, blocking exhaust flow to the intake manifold. The height of the pintle is read by the pintle position sensor, and the control module closes the loop on desired position versus actual position read, changing the pulse width modulated command to the solenoid accordingly, until the actual pintle position equals the desired pintle position.

Basically what is happening is the LEGR is not closing completely and you're getting too much EGR flow when the loop is open. What you can do is pop the valve off and make sure it is clean and not carboned up, a common occurrence for this valve. Once everything is nice and clean, the problem should be fixed. If not then you will need to test out the electronic side of the valve to see if it's a bad valve or one of the sensors.

Additional Information provided courtesy of ALLDATA