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GM/Detroit 6.5L – Engine Management – BOOST CONTROL – Component Operation

BOOST SENSOR (Turbo Only)

Description
The boost sensor (figure 5-44) on turbocharged engines measures fluctuations in intake manifold pressure and vacuum that occur as a result of changes in engine load and engine speed. The sensor is a resistor that converts manifold pressure/vacuum into electrical signals:
• At idle, the boost sensor displays approxi­ mately the same reading as barometric pressure.
• When the engine is at full load with wide open throttle (WOT), manifold pressure is high and vacuum is low. Under these conditions, boost sensor resistance is low.
As a result, a high voltage signal is sent to the PCM telling it to deliver more fuel.
• Conversely, under manifold low pressure conditions, boost sensor resistance is high. This high resistance reduces the strength of the boost signal sent back to the PCM. The PCM then knows to deliver less fuel to the engine.

The PCM uses these signals to determine how much pressure is being produced by the turbocharger. Boost pressure information is used to control fuel delivery and wastegate solenoid operation.

Circuit Operation
The boost sensor receives a constant 5 volt reference signal from the PCM through CKT 416 (figure 5-45). The sensor signal is sent back to the PCM on CKT 432.

Ground for the sensor is provided through the PCM on CKT 452. This ground is shared with the crankshaft position sensor, the ECT sensor, and the IAT sensor.

DTC 61 — “Turbo Boost Sensor Circuit High”
DTC 61 sets when the turbo boost signal voltage is greater than 3.9 volts and engine RPM is less than 3500. A DTC 61 will result in no turbo boost and poor engine performance.

DTC 62 — “Turbo Boost Sensor Circuit Low”
DTC 62 sets when turbo boost signal voltage is less than .8 volt. DTC 62 will result in no turbo boost and limited fuel delivery.

BOOST PRESSURE TEST
1. Remove the front center mounting bolt from the air inlet and install J 39307 adapter with a 6 to 7 foot length of S c ­ inch I.D. rubber line. Then route the rubber line into the cab and connect J 28474 pressure gage to the end of the line.
2. Test drive the vehicle with a passenger watching the gage. Allow the vehicle to coast at engine idle speed in first gear. Then press the accelerator pedal to the floor while the passenger notes the boost pressure reading. A boost reading of 14 kPa (2 psi) or more indicates the turbocharger is operating properly.

 

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