ENGINE EXCHANGE PROGRAM NEW SERIES OF MARK ENGINES

Model and Year: 1991 TRUCKS WITH 7.4L ENGINES

TO: ALL CHEVROLET DEALERS

For 1991, GM has introduced a new series of Mark engines. The displacement is the same as the Mark IV engine that they replaced (7.4L). To gain helpful product feedback when an engine must be replaced, an Engine Exchange Program will be in effect until December 31, 1990.

Only the valve rocker covers and oil pan can be removed to determine whether the engine must be replaced; but before returning the engine, the valve rocker covers and oil pan must be reinstalled. Complete engines are required.

EXCHANGE PROCEDURE:

Once preliminary diagnosis and/or repairs are made and an exchange unit is deemed necessary, call Technical Assistance Network (T.A.N.).

- T.A.N. will require VIN and engine serial number. The engine serial number can be found as shown on the attached illustration.

- T.A.N. will arrange with the Tonawanda Engine Plant to directly ship a replacement engine within 48 hours. The replacement engine will be complete except for acces- sories (i.e., starter, generator, fuel system, etc.).

- T.A. N. will provide a T.A.N. case number for each engine exchange. This number must be recorded on the identification card supplied with the replacement engine and affixed to the replaced engine to be returned. The identification card must be filled out completely.

- The exchange unit must be returned to Tonawanda within 10 days in the original shipping crate to avoid a chargeback.

- The exchange engine must be complete as removed from the vehicle. Dealerships returning incomplete units will be subject to being billed for materials missing.

- Exchange engines should be returned C.O.D. to the Tonawanda Engine Plant. Shipping instructions will be included with the new engine.

Use applicable Labor Operation number and times.

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.