DETONATION AT HIGH MAP /RPM (NEW PROM P/N) 1986

VEHICLES AFFECTED: 1986 DEVILLE/FLEETWOOD, LIMOUSINE AND COMMERCIAL CHASSIS (FEDERAL AND CALIFORNIA) EMISSION SYSTEMS) EXCEPT TOURING COUPE/SEDAN

Some 1986 Front Wheel Drive Deville/Fleetwood, Limousine, and Commercial Chassis vehicles may experience detonation at high RPM and high MAP conditions. Vehicles built after VIN 249254 are equipped with a new PROM to correct this condition. The new PROM supersedes previous service PROM part nubmers for PROM ID's 253/261/254. The new PROMs have revised spark calibratrion for the following ranges of MAP and RPM:

RPM MAP 3200 - 4000 Above 82 kPa 4000 - 4800 Above 72 kPa

The new PROMs can be installed in all 1986 Federal and California Deville, Fleetwood Limousne and Commercial Chassis (except 'Touring' engine). For vehicles built before VIN 249254, the new Service PROM part numbers will repair conditons of detonation that occur in the above MAP and RPM ranges.

Since a number of basic engne mechanical conditions can cause detonation, the cause of the detonation symptom must be corrected to assure proper operation of the vehicle under all conditions. Any detonation condition that does not occur in the above MAP and RPM range should be repaired using the 'Sympton' diagnosis as provided in Section 6E, Subsection B in the 1986 Deville/Fleetwood Service Information Manual before replacing a PROM.

When ordering, use the following part numbers to obtain the new PROM:

Emission Service Prom Supersedes Vehicle System Part No. ID P/N Prom ID ------- ------ --------- -- -- ------- Deville/Fleetwood Federal 16059149 255 16053039 253 Deville/Fleetwood California 16059167 262 16053003 261 Commercial Chassis Fed/Cal 16059163 256 16053022 254

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.