REGULAR UNLEADED FUEL USAGE

VEHICLES AFFECTED: 1990 C,E,K

With introduction of the 4.5L DLPFI engine on 1990 DeVilles, Fleetwoods, Sevilles, and Eldorados, the use of premium unleaded fuel is required. In some areas premium unleaded fuel (minimum of 91 octane) may be unavailable. To allow the vehicles to operate with regular unleaded fuel the base ignition timing must be retarded from 10 DEG to 6 DEG BTDC. The results of retarding the initial timing on vehicle performance is expected to be:

0.2 - 0.4 mpg loss in composite fuel economy. 0.4 - 0.6 second loss in 0-60 mph performance. Weaker feel on heavy wide open throttle accelerations. Flatness on acceleration during cold start and warm up. Potential for trace detonation on high mileage vehicles.

Retarding timing for use with regular unleaded fuel has no effect on:

Durability Engine cooling Idle stability

Vehicles should be returned to proper timing when premium unleaded fuel becomes available. Retarding ignition timing will not be considered possible on some future higher output engines.

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.