Secondary actuators

[ZR100060]

Had my 91 ZR1 one month. While enroute to a local Chevrolet dealership to have all fluids replaced I noticed that my secondaries actuators failed. The dealership tells me they "have three of their best men on it". Just out of curiosity do these things fail all at once, or should it be a more gradual thing. What is the primary reason(s) for these actuators failing. I'm amazed as to how much the cars performance was negatively affected!!!

The longer I have this toy the more questions come up.

 

[Rob]

The following information comes from LT5 Fuel and Emissions, a GM STG Training Course Book, pages 2-12 and 2-13:

Secondary Port Throttle Valves, Actuator and Linkage

"The secondary port throttle valves are used to provide additional control of airflow to the cylinders. The valves are vacuum operated, and controlled by an ECM actuated solenoid, based on input signals from the Throttle Position Sensor (TPS), engine RPM, engine oil temperature sensor and Manifold Absolute Pressure (MAP) sensor. Vacuum is supplied through the vacuum reservoir and vacuum pump. (Refer to Figure 2-14).

In operation, the secondary port throttle valves are closed during low engine speeds and loads, allowing no air path to each cylinder. Additional air is allowed to enter the cylinders at higher RPM when the following criteria are met:

When the TPS indicates to the ECM that the driver has pushed down on the accelerator pedal far enough, and the oil temperature sensor indicates engine oil temperature is within an acceptable range, the ECM will turn "ON" the secondary port throttle actuators through the secondary port throttle control solenoid allowing engine vacuum to be applied to the actuators to open the valves. At the same time, the seondary injectors are turned "ON" to provide additional fuel flow to maintain the correct air/fuel ratio for maxium power (12:1).

The secondary port throttle valves are located in the right and left hand cylinder head (four plates per head). The actuators are mounted to brackets attached near the center of each cylinder head. A common linkage incorporates each set of four throttle valves together to the actuators which will open all throttle valves in unison (Refer to Figure 2-14).

Secondary Port Control Solenoid

This solenoid is used by the ECM to control the application of vacuum to the secondary port throttle valve actuators. The solenoid is normally closed and is opened ("ON") when the ECM provides the ground path. The solenoid is located under the intake plenum at the front of the cylinder block valley, near the left hand side of the vacuum reservoir. The sensor is connected to the engine wiring harness by a two terminal blue connector. (Refer to Figure 2-15)."

 

[Rob]

If the actuators are installed incorrectly, the range of motion on the arms is very limited. Also, the internal rubber seal can wear out and vacuum can leak through. If one fails, do not replace only the one. Replace BOTH valves.

When the mechanic installs the new actuator valves, have him make sure they are installed correctly and they hold a vacuum. This can be done by simply using a hand held vacuum tool which can apply vacuum to the system. He/She should know how to do this according to the service manual.