EBSCO Auto Repair Reference Center INSPECTION AND ADJUSTMENT HEI Systems Fig. 1: Timing marks are found on the crankshaft damper (balancer) and the engine front cover--late model 4.3L engine shown (others similar) Fig. 2: View of a typical timing mark scale Start the engine and allow it to reach operating temperature. Stop the engine and connect the timing light to the No. 1 (left front) spark plug wire, at the plug or at the distributor cap. You can also use the No. 6 wire, if it is more convenient. Numbering is illustrated in this section. NOTE: Do not pierce the plug wire insulation with HEI; it will cause a miss. The best method is to use an inductive pickup timing light. Clean off the timing marks and mark the pulley or damper notch and timing scale with white chalk. Disconnect and plug the vacuum line at the distributor on models with a carburetor. This is done to prevent any distributor vacuum advance. On fuel injected models, disengage the timing connector which comes out of the harness conduit next to the distributor; this will put the system in the bypass mode. Check the underhood emission sticker for any other hoses or wires which may need to be disconnected. Start the engine and adjust the idle speed to that specified on the Underhood Emissions label. With an automatic transmission, set the specified idle speed in Park. It will be too high, since it is normally (in most cases) adjusted in Drive. You can disconnect the idle solenoid, if any, to get the speed down. Otherwise, adjust the idle speed screw. The tachometer connects to the TACH terminal on the distributor and to a ground on models with a carburetor. On models with fuel injection, the tachometer connects to the TACH terminal on the ignition coil. Some tachometers must connect to the TACH terminal and to the positive battery terminal. Some tachometers won't work with HEI. WARNING Never ground the HEI TACH terminal; serious system damage will result. Aim the timing light at the pointer marks. Be careful not to touch the fan, because it may appear to be standing still. If the pulley or damper notch isn't aligned with the proper timing mark (see the Underhood Emissions label), the timing will have to be adjusted. Aim the timing light at the crankshaft damper timing mark, but WATCH OUT for moving engine parts NOTE: Top Dead Center or TDC corresponds to 0°. Before Top Dead Center, BTDC or B may be shown as BEFORE. After Top Dead Center, ATDC, or A may be shown as AFTER. Loosen the distributor base clamp locknut. You can buy specialty wrenches which make this task a lot easier. Turn the distributor slowly to adjust the timing, holding it by the body and not the cap. Turn the distributor in the direction of rotor rotation to retard, and against the direction of rotation to advance. Tighten the locknut. Check the timing again, in case the distributor moved slightly as you tightened it. Reinstall the distributor vacuum line or the timing connector. Correct the idle speed. Stop the engine and disconnect the timing light. Distributor Ignition (DI) Systems 1995 MODELS NOTE: Refer to the underhood label for the proper timing setting. Engage the parking brake, block the wheels and set the transmission in P. Disconnect the Ignition Control (IC) system by disengaging the "set timing connector". This is a single wire sealed connector that has a tan with black stripe lead. This wire comes out of the wiring harness below the heater case. With the ignition switch OFF, connect the timing light pickup lead to the No. 1 spark plug wire. Start the engine and point the timing light at the timing mark on the balancer or pulley and check the timing. If the timing is not within specifications, refer to the underhood emission sticker and loosen the distributor hold-down bolt. Slowly rotate the distributor until the proper timing setting is achieved. Tighten the hold-down bolt and recheck the timing. Turn the ignition OFF, remove the timing light and engage the "set timing" connector. 1996-97 MODELS The ignition timing is preset and cannot be adjusted. If the distributor position is moved, crossfiring may be induced. To check distributor position, do the following: NOTE: An OBD ll compliant scan tool is required for this procedure. With the ignition OFF, attach the scan tool to the Data Link Connector (DLC). Start the engine and bring the vehicle to operating temperature. Monitor cam retard on the scan tool. If cam retard is between -2°and +2°, the distributor is properly adjusted. If cam retard is not between -2°and +2°the distributor must be adjusted. With the engine OFF, loosen the distributor hold-down bolt. Start the engine and check the cam retard reading. Rotate the distributor counterclockwise to compensate for a negative reading and clockwise to compensate for a positive reading. Momentarily raise the engine speed to over 1000 RPM and check the cam retard reading. If the proper reading is not achieved, repeat Steps 7 and 8. When the proper reading has been achieved, tighten the distributor hold-down bolt and disconnect the scan tool. EBSCO Auto Repair Reference Center