LIGHT LOAD DETONATION NEW PROM

Model and Year 1980 CALIFORNIA VEHICLES WITH 3.8L V6 ENGINES (MALIBU)

TO: ALL CHEVROLET DEALERS

Some 1980 vehicles equipped with a 3.8L V6 engine, may exhibit light-load detonation when driving in the 1800 to 2100 RPM engine speed range.

1. After checking all items on the detonation check list below and all confirmed to be within specifications, anew service PROM, P/N 1226931, should be installed, to further assist in repairing this condition.

2. Due to timing curve programming changes within this PROM, the cold fast idle speed will require resetting to specifications, as indicated on the tune-up label.

It is essential that all engine electronic and fuel control systems be checked and set to specifications before the vehicle is released.

DETONATION CHECK LIST

EGR valve system operation Ignition timing Vacuum hoses and/or connection leaks Carburetor for lean operation "dwell" Deposits in combustion chambers Intake valve seals not sealing Thermac air cleaner operation Cooling system problem overheating Incorrect spark plugs Bad fuel EFE valve operation

NOTICE: PROM, P/N 1226931, replaces both previously released P/N 1224682 and 1225438 PROMS. This bulletin also supersedes information provided in bulletin 80-T-92.

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.