1981 DFI IGNITION TIMING ADJ PROCEDURE

1981 DFI IGNITION TIMING ADJUSTMENT

Ignition timing may be adjusted by either of two methods: 1) with conventional strobe timing equipment or, 2) with a probe-type timing advance meter. Both methods are similar to the 1980 methods with exception of the "set-timing" connector. Both methods are explained in full below.

A. Strobe Light Timing

1. Adjust distributor clamp nut to allow distributor to be turned by hand, but without excessive looseness.

2. Insert timing light adapter between the number 1 spark plug and its lead wire. Avoid puncturing the boots or cable cover.

NOTICE: Do not time engine on seven cylinders as the unburned fuel could cause damage to the catalytic converter.

3. Connect a suitable timing light to the adapter. Make sure that timing marks and scribe marks are clean.

4. Connect tachometer to engine and set parking brake securely, place transmission lever in park position.

5. Start engine.

6. When engine is warmed up to normal operating temperature (upper radiator hose hot), open the "set timing" connector.

NOTICE: Do not ground the "set connector on 1981 DFI cars as done on 1980 DEFI models. Grounding the "set timing" connector on 1981 DFI cars may damage the HEI module.

7. With the engine at idle, observe the timing flashes on the pulley in relation to the notches on the front cover. Set the timing to proper specification as shown on emission label under hood on radiator support.

8. Tighten clamp nut to 24 N.m (18 ft. lbs.) and recheck timing to make sure it did not change.

9. Disconnect the tachometer and timing light. Remove adapter and reconnect "set timing" connector.

B. Timing Advance Meter

1. Adjust distributor clamp nut to allow distributor to be turned by hand, but without excessive looseness.

2. Connect power supply for timing meter to battery. Observe correct polarity.

3. Install ignition pickup clip over number 1 spark plug wire. Be sure jaws are clean and locking button is pressed forward to close jaws firmly.

4. Install magnetic pickup in receptacle of timing tab and press down firmly. Pickup should be as close to pulley surface as possible without making contact.

5. Make sure that all leads to advance meter are not near moving parts or exhaust manifold. Place transmission selector lever in the park posi- tion.

6. Turn power switch ON and timing-advance to TIMING position.

7. Start the engine.

8. When engine is warmed up to normal operating temperature (upper radiator hose hot), open the "set timing" connector.

NOTICE: Do not ground the "set timing" connector on 1981 DFI cars as done on 1980 DEFI models. Grounding the "set timing" connector on 1981 DFI cars may damage the HEI module.

9. With the engine speed at idle, observe the ENGINE DEGREES meter and set timing to proper specification as shown on emission label under hood on radiator support.

10. Tighten clamp nut to 24 N.m (18 ft. lbs.) and recheck timing to be sure that it did not change.

11. Disconnect timing advance meter connections from engine and reconnect "set timing" connector.

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.