V 1500 P/U 4WD V8-454 7.4L (1987)
Manifold Pressure/Vacuum Sensor: Customer Interest
Engine - Driveability (Surge)/Emissions
GMC NUMBER:
88-T-141
GROUP. 6E - Engine Emission
DATE:
August, 1988
CORPORATE
NUMBER:
836511R
SUBJECT:
ENGINE DRIVEABILITY (SURGE)
MODELS:
1987-88 C/K, R/V TRUCKS EQUIPPED WITH 7.4L TBI ENGINES (VIN CODE N)
THIS BULLETIN IS BEING REVISED TO INCLUDE PART NUMBER AND SPECIFICATION FOR THE VACUUM HOSE. THIS BULLETIN
CANCELS AND SUPERCEDES TRUCK SERVICE BULLETIN 88-T-81, DATED 3/1/88, ALL COPIES OF WHICH SHOULD BE DESTROYED.
Some 1987-88 C/K, R/V trucks with the 7.4L TBI engine may experience customer comments of poor driveability (surge) on acceleration and at road
speed. If normal diagnostics finds nothing wrong, it may be necessary to reposition the Manifold Absolute Pressure (MAP) sensor. Repositioning of the
MAP sensor will prevent fuel vapor and/or gasoline from entering the MAP sensor under heavy throttle conditions. Vapor or gas in the MAP sensor
causes the sensor to supply lower than normal voltage readings to the ECM. The ECM, when receiving low voltage readings from the MAP sensor,
thinks the engine is rich and leans out fuel, causing engine surge. If it is necessary to reposition the MAP sensor, the following service procedure should
be followed:
