REGULAR UNLEADED FUEL USAGE (PREMIUM FUEL REQUIRED)

SUBJECT: REGULAR UNLEADED FUEL USAGE

This bulletin replaces DSIB 90-1-20 which should be discarded. This bulletin is being revised to include 1991 models.

Use of premium unleaded fuel is required on 1990 4.5L and 1991 4.9L DeVilles, Fleetwoods, Eldorados, and Sevilles. 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' to 6' BTDC. Retarding the initial timing will have a small adverse effect on composite fuel economy and performance.

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.

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.