CAMPAIGN: ENGINE CAM GEAR MISORIENTATION

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

General Motors has determined that certain 1989 M-Vans and 1990 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 cranksbaft gear. This mis-in- dexed cam can result in a lack of performance or backfire. Additionally, the emissions 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 M-Vans and 1990 G- Van, C/K & S/T trucks equipped with 4.3L V-6 engines (RPO LB4) and built within the following VIN breakpoints:

MODEL/YEAR PLANT FROM THROUGH ---------- ------ ---- ------- M-Van 1989 Baltimore KB543944 KB544541 M-Van 1990 Baltimore LB500013 LB500988 G-Van 1990 Lordstown L7500878 L7501500 C/K 1990 Fort Wayne LZ501591 LZ504345 C/K 1990 Pontiac East LE500013 LE501336 S/T 1990 Moraine L2501169 L2502387 S/T 1990 Pontiac West L0501952 L0502211

The specific vehicles involved in this campaign have been identified by Vehicle Identification Number Computer Listings. These listings are fur- nished to all involved dealers with the campaign 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 ensure 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 cor- rection according to instructions contained in this bulletin.

If no owner's name and address were available to GMC Truck Division at the time of campaign initiation, the dealer will determine the owner's name and address from the dealership sales records. Please provide this information directly on the second copy of the listing next to the applicable VIN so that our records may be updated and the appropriate notification mailed to the owner. This second copy should then be submitted to the address listed below in the previously supplied yellow campaign envelopes.

OWNER NOTIFICATION

Owners will be notified of this campaign on their vehicles by GMC Truck Division (see copy of Owner Letter included with this bulletin). A listing of owner names and addresses has been furnished to the involved dealers to enable dealers to follow up with owners involved in this campaign. This listing 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 tbe use of this listing to this campaign.

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 simul- taneously. 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 (BLM) 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.

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.

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

16. Reconnect canister purge line to canister.

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 cranksbaft.

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

e) Remove camsbaft sprocket and chain.

NOTICE: An assistant may be needed to bold cranksbaft 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

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

k) Verify that repair has corrected BLM values by rerunning DIAGNOSTIC PROCEDURE (Steps 1-16).

PARTS INFORMATION

Parts are to be obtained from General Motors Service Parts Operation (GMSPO). To ensure tbat 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 order under an advise code (2).

PART NUMBER DESCRIPTION QUANTITY ----------- ----------- -------- 03754587 Gasket - Water Pump 2 10108435 Gasket - Front Timing Cover 1 14088514 Gasket - Oil Pan 1

WARRANTY INFORMATION

Dealers should submit a warranty claim on each vehicle completed under this campaign.

Labor Operation Time Trouble Number Description Allowance Code ------ ----------- --------- ---- V5610 Inspect - No repair Necessary .3 Hrs 96 (All Models)

V5611 Inspect - Realign timing gear 2.9 Hrs 96 (M-Van witbout A/C)

V5612 Inspect - Realign timing gear 3.1 Hrs 96 (M-Van with A/C)

V5613 Inspect - Realign timing gear 2.8 Hrs 96 (G-Van without A/C or P/S)

V5614 Inspect - Realign timing gear 3.0 Hrs 96 (G-Van with A/C or P/S)

V5615 Inspect - Realign timing gear 3.2 Hrs 96 (G-Van with A/C and P/S)

V5616 Inspect - Realign timing gear 3.0 Hrs 96 (C/K Truck)

V5617 Inspect - Realign timing gear 5.8 Hrs 96 (S Truck without A/C or P/S)

V5618 Inspect - Realign timing gear 6.0 Hrs 96 (S Truck with A/C)

V5619 Inspect - Realign timing gear 5.9 Hrs 96 (S Truck with P/S)

V5650 Inspect - Realign timing gear 6.1 Hrs 96 (S Truck with A/C and PIS)

V5651 Inspect - Realign timing gear 4.4 Hrs 96 (T Truck with A/C and P/S)

V5652 Inspect - Realign timing gear 4.6 Hrs 96 (T Truck with A/C)

* For dealer to receive Administrative Time Allowance associated with this campaign, add 0.1 hour to the Labor Operation Time Allowance.

CAMPAIGN IDENTIFICATION LABEL

Each vehicle corrected in accordance with the instructions outlined in this Product Campaign 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 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.

ADMINISTRATIVE PROCEDURE

Procedures covering this campaign are outlined in Section V of your dealership's "GM Truck Claims Processing Manual" #P 8919.

General Motors has determined that certain 1989 M-Vans and 1990 G-Van, M-Van, C/K & S/T trucks equipped with 4.3L V-6 engines may bave 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 emissions performance of these vehicles may be affected.

To correct this condition on your vehicle, your GMC Truck 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.

Please contact your GMC Truck 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.

Your GMC Truck dealer is best equipped to obtain parts and provide service to ensure your vehicle is corrected as promptly as possible. However, if you take your vehicle to your dealer on the agreed service date and they do not service this condition on that date or within five days, we recommend you contact your nearest GMC Truck Zone Office by telephone. The Zone Office will assist you and your dealer in getting your vehicle corrected. The telephone numbers of the Zone Offices are listed in your Warranty and Owner Assistance Information Manual.

After contacting your dealer and the Zone Office, if you are still not satisfied that we bave done our best to remedy this condition without charge within a reasonable time, you may wish to write 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.

The enclosed owner reply card identifies your vehicle. Presentation of this card to your dealer will assist in making the necessary correction to your vehicle in the shortest possible time. If you have sold or traded your vehicle, please let us know by completing the postage paid owner reply card and returning it to us. 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.