DETONATION/SPARK KNOCK NEW PROM AND TUNE-UP LABEL

Model and Year 1983 CAVALIERS EQUIPPED WITH 2.0L ENGINE (VIN CODE P)

TO: ALL CHEVROLET DEALERS

This cancels and supersedes information contained in Chevrolet Dealer Service Bulletin 83-148 dated February, 1985. This copy identifies an additional PROM application.

This bulletin should be used when detonation (spark knock) is encountered on some 1983 Cavaliers. It should be noted that "burst" detonation (very short periods following a quick throttle movement) is considered acceptable.

1. Check base timing 0 DEG (by-pass disconnected.)

2. Check for proper EGR per chart (see Page 3.)

3. If timing and EGR system checks are satisfactory.

A. On manual transmission vehicles:

Retard base timing to 4 DEG ATDC. Install tune-up label, P/N 14086563.

B. On automatic transmission vehicles:

Install PROM package:

- With Federal emissions and without Cold Startability Revision (reference Chevrolet Dealer Service Bulletin 84-221), P/N 1226823.

- With Federal emissions and with Cold Startability Revision (reference Chevrolet Dealer Service Bulletin 84-221), P/N 1227253.

- With California emissions, P/N 1226984.

Set base timing to 6 DEG BTDC,

Install tune-up label that is included in PROM package.

Use applicable labor operation.

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.