For 1990-2009 cars

# POOR FUEL ECON. AT BREAK-IN UNNECESSARY ADJUSTMENTS

#### VEHICLES AFFECTED: 1986 Devilles, Fleetwoods, Eldorados, and Sevilles

Field reports indicate that ISC, TPS, and/or timing adjustments are sometimes performed unnecessarily on newly delivered 1986 Devilles, Fleetwoods, Eldorados and Sevilles because average fuel economy data displayed on the driver information centre is less than what is expected. Low fuel economy display readings may be normal during the initial break-in period for either of the following reasons:

1. Failure to have 'reset' the fuel data panel during or after the predelivery process may cause low display readings because data accumulated during the final assembly process, transportation and predelivery inspection will be factored into the displayed average fuel economy. Extended periods of idle encountered during this process may be considerably longer than encountered under actual driving conditions and will cause 'low' readings unless this data is deleted from memory by resetting the panel. Resetting the average fuel economy display will not affect the calculated range, but range readings will become more realistic after approximately 25 miles of driving.

2. To improve driveability during the initial break-in period (25 hours on FWD-C and 800 kilometres on E/K), a special calibration has been incorporated into the engine control module which may result in lower fuel economy under some driving conditions. Specifically, the idle speed is raised and low speed application of the viscous converter clutch is prevented until the break-in period has elapsed. This special calibration reverts back to normal calibration specifications automatically after the break-in period.

In order to avoid owner complaints and the unnecessary performance of diagnosis and repairs, it is recommended that the fuel data panels be reset as part of the new car delivery process. Secondly, if concern arises over fuel economy during the initial break-in period, owners should be informed of the special calibration and that fuel economy levels are likely to improve after the break-in period has elapsed.

Due to the 'self adjusting' feature included in 1986 HT4100 engine control software, any efforts to alter idle speed will result in the system either readjusting itself or setting a trouble code.

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.