'FAST START' CRANK SENSOR ADJUSTMENT

VEHICLES AFFECTED: 1988 'C, E, AND H' CARS EQUIPPED WITH 3800 ENGINES (VIN CODE C)

The 1988 3800 V-6 engine is equipped with an improved ignition system which is called a "Fast Start", due to its ability to identify which cylinders to direct spark to within one third (120 degrees) of a crankshaft revolution. Previous C3I systems could take as long as two crankshaft revolutions to synchronize and initiate spark, because they had to wait for the camshaft sensor pulse.

This new ignition system features dual hall effect switches, contained in a single crankshaft position sensor assembly. Dual interrupter rings are mounted on the rear of the crankshaft harmonic balancer. The outer ring has eighteen equally sized and equally spaced teeth while the inner ring has three spaces (windows) which are 10, 20, and 30 degrees in width.

With this new design, exact positioning of the dual hall effect switches (crankshaft sensor assembly) between the interrupter rings is critical. A new crankshaft sensor positioning tool has been developed for this purpose, which will also check the concentricity of both interrupter rings to detect bent vanes that otherwise might go unnoticed by visual inspection. This tool will be released as "Available" in the very near future. If it is necessary to replace the crankshaft sensor and you do not have the tool, the following procedure should be followed:

1. With the harmonic balancer removed, install crankshaft sensor pedestal assembly to engine and torque bolts to 30 N.m (22 lbs. ft.).

2. Loosen the pinch bolt on the new sensor pedestal until the sensor is free to slide in the pedestal.

3. Reinstall harmonic balancer while making sure that both interrupter rings are properly aligned in the crankshaft sensor slots. Torque balancer bolt to 297 N.m (220 lbs. ft.).

4. Rotate the harmonic balancer by hand until one tooth of the outer interrupter ring fills the outer sensor slot.

5. Insert one strip of the crankshaft sensor gap gauge J-36179 between the outer interrupter ring and sensor (See Illustration).

6. Torque sensor retaining pinch bolt to 4 N.m (35 lbs. in.) while maintaining light pressure on sensor against gauge and interrupter ring. This clearance should be checked again at three positions around the interrupter ring, approximately 120 degrees apart. If the interrupter ring contacts the sensor at any point during harmonic balancer rotation, either the sensor is misadjusted or the interrupter ring has excessive runout and must be replaced.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.