CAMPAIGN: ENGINE CAM GEAR MISORIENTATION

Model and Year: 1989 M-VAN & 1990 G-VAN, M-VAN, C/K TRUCK & S/T TRUCK - 4.3L (RPO LB4) V-6 ENGINE

TO: ALL CHEVROLET DEALERS

General Motors has determined that certain 1989 Chevrolet M-Vans & 1990 Chevrolet G-Van, M-Van, C/K & S/T Trucks equipped with 4.3L V-6 engines (RPO LB4) may have been built with the engine cam gear misoriented to the crankshaft gear. This mis-indexed cam can result in a lack of performance or backfire. Additionally, the emission performance of these vehicles may be affected.

To correct this condition, an electronic scanning procedure to identify affected engines will be performed. Once identified, dealers will reorient the camshaft.

VEHICLES INVOLVED

Involved are certain 1989 Chevrolet M-Vans & 1990 G-Van, M-Van, C/K & S/T Trucks equipped with 4.3L V-6 engines (RPO LB4) and built within the following breakpoints:

MODEL/YEAR PLANT FROM THROUGH ---------- ----- ----- ------- M-Van 1989 Baltimore KB270072 KB272407

M-Van 1990 Baltimore LB100001 LB103665

G-Van Lordstown L7101990 L7104322

C/K Fort Wayne LZ105315 LZ113515

" Pontiac East LE100035 LE105424

" Oshawa L1100189 L1101389

S/T moraine L2100010 L2110921

" Pontiac West L0106223 L0106247

Involved vehicles have been identified by Vehicle Identification Number Computer Listings. Computer listings contain the complete Vehicle Identification Number, owner name and address data, and are furnished to involved dealers with the campaign bulletin. Owner name and address data furnished will enable dealers to follow-up with owners involved in this campaign.

These listings may contain owner names and addresses obtained from State Motor Vehicle Registration Records. The use of such motor vehicle registration data for any other purpose is a violation of law in several states. Accordingly, you are urged to limit the use of this listing to the follow-up necessary to complete this campaign. Any dealer not receiving a computer listing with the campaign bulletin has no involved vehicles currently assigned.

OWNER NOTIFICATION

Owners will be notified of this campaign on their vehicles by Chevrolet Motor Division (see copy of owner letter included with this bulletin).

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 correction according to instructions contained in this bulletin.

PARTS INFORMATION

Parts required to complete this campaign are to be obtained from General Motors Service Parts Operations (GMSPO). To ensure these parts will be obtained as soon as possible, they should be ordered from GMSPO on a "C.I.O." order with no special instruction code, but on an advise code (2).

Quantity/ Part Number Description Vehicle ----------- ----------- ------- 03754587 Gasket - Water Pump 2

10108435 Gasket - Front Timing Cover 1

14088514 Gasket - Oil Pan 1

SERVICE PROCEDURE

DIAGNOSTIC PROCEDURE

1) Connect SCAN tool or CAMS machine to vehicle. Make sure scan tool is in ROAD TEST mode.

If using a TECH 1 scan tool, it should be set up to display BLOCK LEARN (BLM) values and CLOSED/OPEN LOOP status simultaneously. This can be done by scrolling through the preprogrammed pairs of parameters with YES or NO key until a pair is found with BLOCK LEARN. Fix BLOCK LEARN by pressing "FO" if BLOCK LEARN is top parameter, "F1" if it is bottom parameter. Then continue scrolling other half of the display with either YES or NO key until CLOSED/OPEN LOOP status parameter is displayed. To "unfix" top parameter, press "F1". Press "FO" to "unfix" lower parameter.

If using a CAMS machine, select Dynamic Display Option. This will display both BLOCK LEARN (BLM) and OPEN/CLOSED LOOP status.

2) Disconnect canister purge line at the canister, see Figure 1.

3) Apply parking brake.

4) Place automatic transmission equipped vehicles in PARK and manual transmission equipped vehicles in NEUTRAL.

5) Start engine and warm up so that coolant temperature is at least 85 degrees C.

6) Make sure air conditioning system is OFF.

7) Make sure vehicle is in CLOSED LOOP mode.

8) Raise engine speed to 2600 RPM and maintain speed.

9) Monitor BLOCK LEARN (BIM) values and CLOSED LOOP status at 2600 RPM - wait at least 30 seconds for BLM values to stabilize.

10) If BLM value at 2600 RPM is less than 115, the timing chain sprockets are misaligned. Realign timing chain sprockets following REPAIR PROCEDURE section of this bulletin (pages 5-6).

11) If 2600 RPM BLM value is 115 or greater, let engine idle - automatic transmission equipped vehicles in DRIVE and manual transmission equipped vehicles in NEUTRAL.

12) Make sure system is still in CLOSED LOOP before continuing, if not, return to step #7 and rerun testing sequence.

13) Monitor BLM values and CLOSED LOOP status at IDLE - wait at least 30 seconds for BLM value to stabilize.

If system switches to OPEN LOOP too soon, rewarm oxygen sensor by shifting transmission to NEUTRAL or PARK and raise engine speed to 1500 RPM until system switches to CLOSED LOOP STATUS.

14) If idle BLM value is less than 115, the timing chain sprockets are misaligned. Realign timing chain sprockets following REPAIR PROCEDURE section of this bulletin (pages 5-6).

15) If both BLM values are greater than 115, no repairs are required.

16) Reconnect canister purge line to canister.

17) Install Campaign Identification Label.

REPAIR PROCEDURE

NOTICE: Perform repair procedure only if BLM values from diagnosis are less than 115 at 2500 RPM or idle.

a) Remove spark plugs.

b) Remove front timing chain cover - see section 6A3 in appropriate service manual.

NOTICE: It is not necessary to replace front crankshaft seal.

c) Thread a 7/16" x 20 x 1.00" bolt and torsional damper washer into crankshaft.

d) Rotate crankshaft in a clockwise direction (by placing a socket or wrench on previously installed bolt) until timing mark on camshaft sprocket is pointing straight down toward crankshaft.

e) Remove camshaft sprocket and chain.

NOTICE: An assistant may be needed to hold crankshaft in place (with chain still installed) to avoid movement of camshaft sprocket during removal.

f) Rotate crankshaft in a clockwise direction until timing mark on crankshaft is pointing straight up toward camshaft.

g) Reinstall camshaft sprocket and timing chain.

NOTICE: Properly aligned timing marks are shown in Figure 2.

h) Tighten camshaft sprocket bolts to 17 ft. lbs. (23 Nm).

i) Reinstall timing cover with a new gasket (P/N 10108435) - see section 6A3 in appropriate service Manual for reinstallation details.

NOTICE: Install new oil pan gasket (P/N 14088514) and new water pump gaskets (P/N 3754587).

j) Reinstall spark plugs - tighten to 22 ft. lbs. (30 Nm).

k) Verify that repair has corrected BLM values by rerunning diagnostic procedure (steps 1-17).

CAMPAIGN IDENTIFICATION LABEL

Each vehicle corrected in accordance with the instructions outlined in this bulletin will require a "Campaign Identification Label." Each label provides a space to include the five (5) digit dealer code of the dealer performing the campaign service. This information may be inserted with a typewriter or a ball point pen.

Each "Campaign Identification Label" is to be located on the radiator core support in an area which will be visible when the vehicle is brought in for periodic servicing by the owner.

Apply "Campaign Identification Label" only on a clean dry surface.

CLAIM INFORMATION

Submit a Product Campaign Claim with the information indicated below:

* Failed Parts Labor Lab Oth Repair Performed PC Part No. Allow CC-FC OP Hrs Hrs ---------------- -- -------- ----- ----- -- --- ---

Inspect/no repair SK-00 V5610 0.3 0.1 necessary - all models

Inspect/realign 4 14088514 ** SK-00 V5611 2.9 0.1 timing gear M-Van w/out A/C

Inspect/realign 4 14088514 ** SK-00 V5612 3.1 0.1 timing gear M-Van with A/C

Inspect/realign 4 14088514 ** SK-00 V5613 2.8 0.1 timing gear G Van w/out A/C or P/S

Inspect/realign 4 14088514 ** SK-00 V5614 3.0 0.1 timing gear G-Van with A/C or P/S

Inspect/realign 4 14088514 ** SK-00 V5615 3.2 0.1 timing gear G-Van with A/C and P/S

Inspect/realign 4 14088514 ** SK-00 V5616 3.0 0.1 timing gear C/K Trk.

Inspect/realign 4 14088514 ** SK-00 V5617 5.8 0.1 timing gear S-Truck w/out A/C or P/S

Inspect/realign 4 14088514 ** SK-00 V5618 6.0 0.1 timing gear S-Truck with A/C

Inspect/realign 4 14088514 ** SK-00 V5619 5.9 0.1 timing gear S-Truck with P/S

Inspect/realign 4 14088514 ** SK-00 V5650 6.1 0.1 timing gear S-Truck with A/C and P/S

Inspect/realign 4 14088514 ** SK-00 V5651 4.4 0.1 timing gear T-Truck w/out A/C and P/S

Inspect/realign 4 14088514 ** SK-00 V5652 4.6 0.1 timing gear T-Truck with A/C

*Campaign Administrative Allowance

*The "Parts Allowance" should be the sum total of the current GMSPO Dealer Net price plus 30% of all parts required for the repair.

Dealers will automatically receive the correct labor and material allowance based on the labor operation performed. Refer to the Chevrolet Claims Processing Manual for details on Product Campaign Claim Submission.

This notice is sent to inform you that Chevrolet Motor Division is conducting a recall campaign that includes your vehicle.

REASON FOR THIS RECALL

General Motors has determined that your 1989 or 1990 Chevrolet Vehicle equipped with a 4.3L V6 engine may have been built with the engine cam gear mis-indexed to the crankshaft gear. This misoriented cam gear can result in a lack of engine performance or backfire. Additionally, the emission performance of these vehicles may be affected.

WHAT WE WILL DO

To correct this condition on your vehicle, your Chevrolet dealer will use an electronic scanning procedure to identify affected engines. The dealer will then reorient the camshaft on those vehicles determined to have this condition. This service will be provided for you at no charge.

WHAT YOU SHOULD DO

Please contact your Chevrolet dealer as soon as possible to arrange a service date. Instructions for making this correction have been sent to your dealer. Please ask your dealer if you wish to know how much time will be needed to schedule, process and repair your vehicle.

The enclosed owner reply card identifies your vehicle. Presentation of this card to your dealer will assist in making the necessary inspection/correction in the shortest possible time. If you have sold or traded your vehicle, please let us know by completing the postage paid reply card and returning it to us. Should your dealer not schedule a service date within a reasonable time, you should contact the Chevrolet Customer Assistance Center by calling 1-800-222-1020.

If your dealer and the Customer Assistance Center are unable to remedy this condition within a reasonable time, you may wish to advise the Environmental Protection Agency, at the following address: Director, Manufacturer's Operations Division (EN-340F), United States Environmental Protection Agency, 401 M Street. S.W., Washington, D.C. 20460. To ensure your full protection under the emission warranty made applicable to your vehicle by Federal Law, and your right to participate in future recalls, it is recommended that you have your vehicle serviced as soon as possible. Failure to do so could legally be determined to be lack of proper maintenance of your vehicle. Also, your vehicle may fail a state or local emission inspection test if this recall work is not accomplished.

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

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.