CRUISE CONTROL TRANSDUCER DIAGNOSIS & CORRECTION

A RECENT ANALYSIS OF TRANSDUCERS RETURNED TO AC DELCO REPAIR STATIONS INDICATES THAT MANY TRANSDUCERS COULD HAVE BEEN ADJUSTED ON THE VEHICLE. THE FOLLOWING INFORMATION WILL ASSIST TECHNICIANS IN DIAGNOSING AND CORRECTING MOST ABNORMAL CRUISE CONTROL CONDITIONS. COMPLETE DETAILS FOR NORMAL SERVICE ARE FOUND IN THE SERVICE MANUAL. 1.VEHICLE LOSES SPEED UPHILL AND GAINS SPEED DOWNHILL A.POSSIBLE CAUSE (DIESEL EQUIPPED): LOOSE SERVO TO CARBURETOR LINKAGE OR MISADJUSTED THROTTLE LINKAGE OR T.V. CABLE. CORRECTION: THE THROTTLE LINKAGE AND THE T.V. CABLE MUST BE ADJUSTED PROPERLY AS OUTLINED BELOW: A.CHECK TIMING, ADJUST IF NEEDED. B.REMOVE CLIP FROM CRUISE CONTROL THROTTLE ROD AND DISCONNECT THE ROD FROM THE THROTTLE LEVER ASSEMBLY. C.DISCONNECT THE TRANSMISSION T.V. (OR DETENT) CABLE FROM THE THROTTLE ASSEMBLY. D.LOOSEN THE LOCK NUT ON THE PUMP ROD AND SHORTEN SEVERAL TURNS. E.ROTATE THE LEVER ASSEMBLY TO THE FULL THROTTLE POSITION AND HOLD IN THAT POSITION. F.LENGTHEN THE PUMP ROD UNTIL THE INJECTION PUMP LEVER JUST CONTACTS THE FULL THROTTLE STOP. G.RELEASE THE LEVER ASSEMBLY AND TIGHTEN THE PUMP ROD LOCK NUT. H.REMOVE THE PUMP ROD FROM THE LEVER ASSEMBLY. I.RECONNECT THE TRANSMISSION T.V. OR DETENT CABLE FIG. 1. J.DEPRESS AND HOLD THE METAL LOCK TAB ON THE CABLE UPPER END. MOVE THE SLIDER THROUGH THE FITTING IN THE DIRECTION AWAY FROM THE LEVER ASSEMBLY UNTIL THE SLIDER STOPS AGAINST THE METAL FITTING. K.RELEASE THE METAL TAB, ROTATE THE LEVER ASSEMBLY TO THE FULL THROTTLE STOP AND RELEASE THE LEVER ASSEMBLY. L.RECONNECT THE PUMP ROD (AND CRUISE CONTROL THROTTLE ROD). M.REMOVE THE CONNECTOR FROM THE FAST IDLE SWITCH AND BRIDGE THE HARNESS CONNECTOR WITH A JUMPER. DO NOT ALLOW THE JUMPER TO TOUCH GROUND. N.WITH THE DRIVING WHEELS BLOCKED AND THE PARKING BRAKE ON, START THE ENGINE AND ADJUST THE SOLENOID (ENERGIZED) TO THE SPECIFICATION LISTED ON THE EMISSION CONTROL INFORMATION LABEL. O.CHECK AND ADJUST THE SLOW IDLE SPEED WITH THE ENGINE AT OPERATING TEMPERATURE. TO CHECK IDLE SPEEDS, IT WILL BE NECESSARY TO INSERT THE PROBE OF THE MAGNETIC PICKUP TACH. J-26925 IN THE TIMING INDICATOR HOLE. P.WITH THE DRIVING WHEELS BLOCKED AND THE PARKING BRAKE ON, ADJUST THE SLOW IDLE SCREW ON THE INJECTION PUMP TO THE SPECIFICATION SHOWN ON THE EMISSION CONTROL LABEL. Q.IF EQUIPPED WITH CRUISE CONTROL ADJUST THE SERVO THROTTLE ROD TO MINIMUM SLACK (ENGINE OFF) THEN PUT CLIP IN FIRST FREE HOLE CLOSEST TO THE BELLCRANK, BUT WITHIN THE SERVO BAIL. THIS ADJUSTMENT SHOULD BE MADE TO ACHIEVE A MINIMUM AMOUNT OF SLACK IN THE LINKAGE ON CLIP HOWEVER NOT SO TIGHT AS TO EFFECT THE HOT IDLE SPEED. B.POSSIBLE CAUSE: CHECK FOR VACUUM HOSE LOOSE, PINCHED OR DISCONNECTED. CORRECTION: A.CORRECT VACUUM HOSES AS REQUIRED. B.IF EQUIPPED WITH DIESEL, ALSO CHECK VACUUM REGULATOR VALVE FOR PROPER OPERATION. C.IF EQUIPPED WITH VACUUM PUMP (MW9 TRANSMISSION - 4 SPEED), CHECK FOR STUCK OR IMPROPERLY INSTALLED CHECK VALVE. C.POSSIBLE CAUSE: LOOSE BEAD CHAIN OR LINKAGE AT POWER UNIT (SERVO) CORRECTION: REMOVE SLACK BY ADJUSTING BEAD CHAIN OR LINKAGE AS TIGHT AS POSSIBLE, BUT NOT SO TIGHT SO AS TO AFFECT HOT IDLE SPEED. 2.INOPERATIVE SYSTEM A.POSSIBLE CAUSE: MISADJUSTED BRAKE RELEASE SWITCH AND/OR VACUUM RELEASE VALVE. CORRECTIVE ACTION: ADJUST AS PER MANUAL. SECTION 9 OF SKYLARK SERVICE MANUALS AND SECTION 9B OF FULL SIZE SERVICE MANUALS. B.POSSIBLE CAUSE: LOOSE, DISCONNECTED, OR PINCHED VACUUM HOSES. CORRECTIVE ACTION: REPLACE OR REPAIR AS REQUIRED. 3.VEHICLE CRUISES ABOVE OR BELOW ENGAGEMENT SPEED. POSSIBLE CAUSE: ORIFICE TUBE AND VALVE ASSEMBLY (REGULATED AIR BLEED) MISADJUSTED. CORRECTION: A.ENGAGE CRUISE CONTROL AT EXACTLY 50 MPH. B.IF CAR CRUISES BELOW ENGAGEMENT SPEED, SCREW ORIFICE TUBE OUTWARD. C.IF CAR CRUISES ABOVE ENGAGEMENT SPEED, SCREW ORIFICE TUBE INWARD. EACH 1/4 TURN OF THE ORIFICE TUBE WILL CHANGE CRUISE SPEED APPROXIMATELY ONE MPH. SNUG-UP LOCK NUT AFTER EACH ADJUSTMENT BEFORE TESTING. SEE PAGE 9B-9 OF THE 1981 CHASSIS SERVICE MANUAL - ALL SERIES EXCEPT SKYLARK. FOR SKYLARK SEE PAGE 9-4. 4.BROKEN LOWER FLEX SHAFT (DRIVE CABLE). POSSIBLE CAUSE: HIGH TORQUE CONDITION IN SPEEDO CABLE BECAUSE OF KINK OR INTERFERENCE. THE TRANSDUCER IS NOT LIKELY TO CAUSE THIS PROBLEM AND SHOULD NOT BE REPLACED. MAKE SURE THAT A BROKEN PIECE OF THE CABLE DOES NOT REMAIN IN TRANSDUCER BEFORE INSTALLATION OF NEW CABLE.

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.