Vacuum Operated Engine Mounts Description and Operation: Notes
The system consists of the following components:
- Engine mounts (Qty: 2)
- Vacuum tank assembly
- Valve assemblies (Qty: 2)
- Filter assembly
- An engine mount vacuum hose assembly (includes a check valve)
The vacuum switchable engine mounts each have two vacuum line ports. The port inside the larger opening on each engine mount is the vacuum port 1. The port inside the smaller opening is the vacuum port 2. The vacuum port 1 receives the larger diameter straight connector. The vacuum port 2 receives the smaller diameter 90 degree connector. By design, the vacuum port 1 connector will not fit onto the vacuum port 2. The vacuum switchable engine mounts have four states or operation modes, only three of which are used. The states that are used are Idle, Driveaway, and Smooth Road Shake (SRS).
The table below describes which ports receive vacuum during each state.
| - | Idle State | Driveaway State | SRS State |
|---|---|---|---|
| Engine Mount Solenoid Valve - Right | VACUUM ON | VACUUM OFF | VACUUM ON |
| Engine Mount Solenoid Valve - Left | VACUUM ON | VACUUM OFF | VACUUM OFF |
The application of vacuum to the engine mount ports is controlled by two valve assemblies. These valve assemblies are ON or OFF electric solenoids. One valve assembly controls vacuum to the vacuum port 1, and the other one controls vacuum to the vacuum port 2. The valve assemblies are powered for 30 seconds after key off.
When the valve assembly is OFF, it is considered closed. There is no vacuum being applied to either of the vacuum ports on the engine mount. Instead, the engine mount is venting to atmosphere. When the valve assembly is commanded ON, the solenoid is open and there is vacuum applied to either of idle engine mount vacuum ports.
The engine mount vacuum hose assembly includes a filter assembly that captures dust particles, allowing only fresh air into the system. The filter assembly also prevents water from entering the system. The filter assembly protects the internals of the valve assemblies, engine mounts, vacuum lines, and tank. The filter assembly does not require maintenance.
If needed, vacuum is received from the intake manifold. It flows through the tank assembly, which also reserves vacuum. It then flows through the open valve assemblies to the engine mount ports which lead to two separate vacuum chambers inside the mount.
The total engine mount vacuum system must be replaced if glycol fluid is found anywhere in the system. Glycol fluid will damage system components and cause them to fail.
The engine mounts are filled with glycol fluid. The fluid is pushed back and forth through different paths in the engine mount by the main rubber element at the top of the engine mount. The fluid flows through the idle and/or bounce tracks/paths which impacts the stiffness and damping of the engine mounts. To control the flow of fluid through the tracks vacuum is turned off and on under two separate diaphragms.
The engine mounts, valve assemblies, vacuum tank assembly, and filter assembly are all serviced separately. The vacuum hoses, connectors and check valve are serviced as one hose assembly kit.
The engine mount software is in the Chassis Control Module (CCM). Vehicle operating data is received over the GMLAN. The (CCM) determines the appropriate state for the engine mounts based off the vehicle operating conditions.
The engine mounts are in the Idle state if the vehicle speed is less than 14 km/h (9 mph) and engine speed is greater than 300 RPM. The engine mounts are in the Smooth Road Shake (SRS) state if vehicle speed is between 105 - 137 km/h (65 - 85 mph) or if the engine speed is less than 300 RPM. Finally, the engine mounts are in the Driveaway state if the vehicle speed is between 14 - 105 km/h (9 - 65 mph), or above 137 km/h (85 mph). If a fault is detected in the system, the default mount state is the Driveaway state.