S10/T10 Blazer 4WD V6-262 4.3L (1989)
Inspect
1. The hose connections at the vacuum actuators, control head valve and vacuum tank.
2. The vacuum source circuit:
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Install a vacuum tee and gage (with restrictor) at the vacuum tank outlet. Idle the engine and read the vacuum (a normal vacuum is equivalent
to manifold vacuum) at all selector lever positions.
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Vacuum less than normal at all positions. Remove the tee and connect the vacuum gage line to the tank - read the vacuum. If still low, then the
problem lies in the feed circuit, the feed circuit to the tank or in the tank itself. If vacuum is now normal, then the problem lies downstream.
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Vacuum less than normal at some positions. If vacuum was low at one or several of the selector lever positions, a leak is indicated in these
circuits.
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Vacuum normal at all positions. If vacuum was normal and even at all positions, then the malfunction may be caused by improperly connected
or plugged lines or a malfunctioning vacuum valve or valves.
3. Specific vacuum circuit check:
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Place the selector lever in the malfunctioning position and check for vacuum at the pertinent vacuum actuators.
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If vacuum exists at the actuator but the door does not move, then the actuator is defective or the door is mechanically bound.
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If low or no vacuum exists at the actuator determine whether the cause is the vacuum harness or the vacuum valve.
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Check the vacuum harness first.
4. Vacuum harness circuit check:
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Disconnect the vacuum harness at the control head.
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The black line should show engine vacuum; if not, trace back through connector to vacuum tank.
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To check any individual circuit, place the selector lever at the involved circuit position and check for vacuum presence.
