Engine - Spark Knock, Poor Performance
86chevy16NUMBER: 86-B-77
GROUP: 6D - Engine Electrical
DATE: April, 1986
SUBJECT: SPARK KNOCK (PREIGNITION)
MODELS: 1984-85 C, K, G TRUCKS EQUIPPED WITH THE LE9 5.0L, LF3 5.0L, OR LS9 5.7L ENGINE AND ELECTRIC SPARK CONTROL (ESC) FEDERAL EMISSIONS AND ELECTRONIC SPARK TIMING (EST) CALIFORNIA EMISSIONS.
THIS BULLETIN CANCELS AND SUPERSEDES 86-B-21 (DECEMBER, 1985) ALL COPIES OF WHICH SHOULD BE DESTROYED.
Some 1984-85 vehicles equipped with the LE9 5.0L (VIN Code H), LF3 5.0L (VIN Code F), or LS9 5.7L (VIN Code L) engine may experience detonation (preignition) or poor performance when operating in a loaded condition or pulling a grade. As a result of the preignition, the ESC (Federal) or EST (California) retards the spark timing, and a noticeable reduction in performance may occur. In the event the preignition condition is not corrected by the ESC/EST spark retard, continued operation under these conditions could result in internal
engine damage. To reduce the possibility of this occurrence, the spark plugs should be changed to a colder heat range. When these conditions exist, the original equipment (R44TS) spark plugs should be replaced with R43CTS (P/N 5613810). The correct spark plug gap is .045". Starting with 1986 vehicles, the LE9, LF3, LS9, and LT9 engines are built with the R43CTS spark plugs.