CAMPAIGN: REPLACEMENT PROM INCORRECT COMPRESSION RATIO

INCORRECT COMPRESSION RATIO

MODELS: 1987 G30 Van over 8,500# w/5.7L Engine (RPO L05, VIN Code K) and 3 Speed Automatic Transmission

General Motors of Canada Limited has determined that certain .G30 model vans may have been produced with an engine compression ratio of 9.3:1 rather than. 8.6:1 as intended. While there is an improvement in performance, this condition may, result in spark knock.

To minimize the possibility of spark knock, new PROMS have been released with revised spark advance calibrations which will allow proper engine operation at the increased compression ratio.

VEHICLES INVOLVED:

Involved are certain 1987 G30 model vans over 8,500# and equipped with 5.7L engines (RPO L05, VIN Code K) and 3 speed automatic transmission (RPO M40) built within the following parameters:

CHEV From Through ---- ---- -------

Lordstown SOP H7119304

Scarborough SOP H4106259

GMC

Lordstown SOP H7504664

Scarborough SOP H4502455

All affected vehicles have been identified by the VIN listing provided to involved Dealers with this bulletin. Any Dealer not receiving a listing was not shipped any of the affected vehicles.

DEALER CAMPAIGN RESPONSIBILITY:

Dealers are to service all vehicles subject to this campaign at no charge to owners, regardless of mileage, age of vehicle, or ownership, from this time forward.

Whenever a vehicle subject to this campaign is taken into your new or used vehicle inventory, or it is in your Dealership for service in the future, you should take the steps necessary to be sure the campaign correction has been made before reselling or releasing the vehicle.

Owners of vehicles recently sold from your new vehicle inventory are to be contacted by the Dealer, and arrangements made to make the required modification according to instructions contained in this bulletin.

CAMPAIGN PROCEDURE:

Refer to Section 4 of the Service Policies and Procedures Manual for the detailed procedure on handling Product Campaigns. Dealers are requested to complete the campaign on all transfers gas soon as possible.

OWNER NOTIFICATION:

All owners of record at the time of campaign release are shown on the attached computer listing and have been notified by first class mail from General Motors. The listings provided are for campaign activity only and should not be used for any other purpose.

PARTS INFORMATION:

Parts required for this modification can be obtained through regular channel as follows:

Part Number Description Quantity/Vehicle ---------- ----------- -----------------

1228417 PROM 1

PARTS AND LABOUR CLAIM INFORMATION:

Credit for the campaign work performed will be paid upon receipt of a properly completed campaign claim card, RAPID terminal or DCS transmission in accordance with the following:

Repair Code Description Time Allowance ----------- ----------- --------------

2A Replace PROM .6

Time allowance includes 0.1 hour for Dealer administrative detail associated with this campaign. Parts credit will be based on Dealer net plus 30% to cover parts handling.

SERVICE PROCEDURE:

Replace original PROM with new P/N 1228417 PROM. Refer to the 1987 Light Quty Truck Fuel Driveability and Emissions service Manual (ST-378-87), section 3-103 (Figure 3-39) for instructions on PROM servicing.

INSTALLATION OF CAMPAIGN IDENTIFICATION LABEL

Clean surface of radiator upper mounting panel and apply a Campaign Identification Label. Make sure the correct campaign number is inserted on the label. This will indicate that the campaign has been completed.

Dear General Motors Customer:

General Motors of Canada has determined that certain G30 model vans may have been produced with an engine compression ratio or 9.3:1 rather than 8.6:1 as intended. This condition can cause spark knock.

To correct this condition, the calibrator in your vehicles Electronic Control Module (ECM) will be replaced. The new calibrator contains revised engine calibration information which will allow your engine to operate properly at the increased compression ratio.

Instructions for this correction have been sent to your Dealer. The labor time to perform this service is approximately 1/2 hour. Please ask your Dealer if you wish to know how much additional time will be needed to process your vehicle.

This letter identifies your vehicle. Presentation of this letter to your Dealer will assist their Service personnel in completing the necessary correction to your vehicle in the shortest possible time.

Further assistance, if required, may be obtained from the General Motors Zone Office nearest you. Your vehicle Owner's Manual provides the location and phone number of each respective Zone Office.

We are sorry to cause you this inconvenience; however, we have taken this action in the interest of your continued satisfaction with our products.

Technical Services Department General Motors of Canada Limited

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.