LOSS OF PWR. DUE TO VAPOR LOCK (INSTALL NEW VAPOR LOCK KIT)

SUBJECT: LOSS OF POWER DUE TO VAPOUR LOCK (INSTALL VAPOUR LOCK KIT)

VEHICLES AFFECTED: 1985-88 MEDIUM DUTY TRUCK CHASSIS P6T042 W/5.7L/6.OL/7.OL AND 30/60 U.S. GALLON TANKS

* REFER TO PRODUCT SERVICE BULLETIN 866309 - 88-6-509 FOR * SCHOOL BUS APPLICATIONS

Some 1985-1988 subject model vehicles may experience an intermittent loss of engine power due to fuel line vapour lock when operated during high ambient temperatures and/or heavy load conditions.

Listed below are some of the conditions experienced when vapour lock occurs:

1. Loss of engine power when hot, but operates properly after sitting several hours or overnight.

2. Engine will not continue to run.

3. Long starter crank times when attempting to start a hot engine.

Vapour lock occurs when fuel in the line vaporizes. Because the engine mechanical fuel pump is actually a liquid suction pump, when this condition occurs the fuel pump efficiency may be greatly reduced or the pump may become inoperative. One way to eliminate the effects of vapour lock is to push the fuel to the engine mechanical fuel pump with an electric pump.

Service has released an in-tank electric fuel pump kit which incorporates an electric pump, fuel gauge sender, wiring harness and an electric pump/control module. This will increase the performance of the engine when operated in high ambient temperatures or under heavy load conditions.

To eliminate the vapour lock condition, the change will require the ordering and installation of three (3) separate part numbers which are determined by the vehicle RPO content. These three (3) separate parts are listed below:

1. Fuel Tank Sender Assembly

2. Electric Pump Assembly

3. Vapour Lock Installation Kit

Adequate care must be used when ordering parts to make this change to insure proper installation and results. See Parts List contained in this bulletin.

SERVICE PROCEDURE

1. IN-TANK FUEL PUMP INSTALLATION

Listed below are three separate service procedures which can be used to remove/install electric in-tank fuel pumps, depending on the body, fuel tank capacity, and wheel base.

IMPORTANT: To help prevent a fire or personal injury when working on the fuel system, disconnect the vehicle battery ground(-) cable(s) and be sure fire fighting and safety equipment as required by any local fire and safety regulations and dealership policies are available.

A. In-tank pump installation if body is equipped with a fuel tank sending Unit access hole.

1. Remove four screws and access plate (plate may be secured to the floor with sealer and may have to be pried loose).

2. Disconnect fuel sender wire and fuel lines.

3. Remove seven mounting screws, washers and mounting ring from sender and retain.

4. Remove sender and gasket from tank and discard.

5. Clean gasket mounting area thoroughly and install new gasket (3) (Figure 1).

6. Follow instructions supplied for assembly of fuel pump to sending unit and then install sender/pump assembly. Reinstall mounting screws, washers and mounting ring (Figure 1).

7. Reconnect fuel lines and existing sender connector (Figure 1).

8. Route one end of fuel pump feed wire (4) from service kit through existing wiring grommet in frame and connect to sender/pump connector (Figure 1).

9. Re-install cover plate using sealer between plate and floor.

B. IN-TANK PUMP INSTALLATION ON VEHICLES EQUIPPED WITH THE FOLLOWING OPTIONS WITHOUT BODY ACCESS HOLE.

With 60 gallon fuel tank (PZP) and 167" (FYL) or 179" (FNQ) or 189" (FWS) or 203" (FPQ) or 209" (FPU) wheel base.

1. Drain fuel from fuel tank.

2. Remove fuel line bracket and grommets in frame at fuel sender location (Figure 1).

3. Pull lines through frame until clamps are accessible. Remove clamps and disconnect hoses.

4. If sender wires cannot be disconnected, cut sender wires at easily accessible point inside of frame channel.

5. Disconnect fuel tank vent valve from bracket at tank. This valve is secured with rose bud clips which must be compressed to slip valve out of bracket.

6. Remove outboard nuts securing the two tank mounting straps and pull studs out of mounting holes.

7. Slide tank out of saddle brackets to rear of vehicle on 60 gallon tank. Tank must be lifted up and tilted at outboard side so drain plug at bottom can clear saddle brackets and so vents on top of tank can clear the floor braces. Two technicians may be required for this step.

IMPORTANT: When tank is half way out, the rear half may need to be supported by Dolly Jack to complete removal.

8. Remove seven mounting screws, washers and mounting ring from sender and retain.

9. Remove sender and gasket and discard. Save old connector and wires which were cut off at Step 3.

10. Clean gasket mounting area thoroughly and install new gasket (3).

11. Follow instructions supplied for assembly of fuel pump to sending unit and then install sender/pump assembly reinstall mountings, screws, washers and mounting ring (Figure 1).

12. Connect existing sender connector to new sender/pump connector (1). wires will be spliced when tank is re- installed (Figure 1).

13. Route one end of fuel pump feed wire (4) from service kit through existing wiring grommet in frame and connect to sender/pump connector (Figure 1).

14. Slide fuel tank back into brackets.

15. Reconnect fuel lines and install grommets (Figure 1).

16. If sender wires were cut, splice wires back together. Use staggered splice clips and double wrap securely with vinyl tape.

17. Center tank properly in brackets and reinstall tank rear end support brackets.

18. Reinstall two inside tank mounting straps on 60 gallon tank.

19. Reinstall nuts on tank mounting straps. Torque to 40-51 mm (30-38 lbs/ft).

C. IN-TANK PUMP INSTALLATION ON VEHICLES EQUIPPED WITH THE FOLLOWING OPTIONS WITHOUT BODY ACCESS HOLE.

With 30 gallon fuel tank (PZJ) or 137" (FWD) or 167" (FYL) or 179" (FNQ) or 203" (FPQ).

1. Drain fuel from fuel tank.

2. Remove fuel line bracket and grommets in frame at fuel sender location (Figure 1).

3. Pull lines through frame until clamps are accessible. Remove clamps and disconnect hoses.

4. If necessary, install a jack and wooden blocks under fuel tank support.

5. Remove and retain the 4 nuts, bolts and washers holding the fuel tank mounting brackets to the frame. Remove vent filter bracket with tank mounting bracket.

6. Carefully lower tank sufficiently to gain access fuel sender unit.

7. Disconnect fuel sender unit wire at tank unit.

8. Slide fuel tank outboard from frame if necessary for access to sender unit.

9. Remove seven mounting screws, washers and mounting ring from sender and retain.

10. Remove sender and gasket and discard.

11. Clean gasket mounting area thoroughly and install new gasket.

12. Follow instructions supplied for assembly of fuel pump to sending unit and then install sender/pump assembly. Reinstall mounting screws, washers and mounting ring (Figure 1).

13. Connect existing engine harness sender connector to new sender/pump connector (Figure 1).

14. Route one end of fuel pump feed wire (4) from service kit through existing wiring grommet in frame and connect to pump connector on sender/pump assembly (Figure 1).

15. Raise tank and mounting brackets to proper height for mounting and center fuel tank.

16. Reconnect fuel lines, fuel line bracket or clip and reinstall grommets (Figure 1).

17. Reattach mounting brackets to frame with existing hardware along with vent filter bracket. Torque nut to 60-81 Nm (44-60 lbs/ft).

2. ELECTRICAL MODULE ASSEMBLY AND FUEL PUMP WIRE ASSEMBLY

IMPORTANT: Figure 2 will assist in the assembly of the electrical module.

A. Unplug two (2) existing alarm module assembly connectors from instrument panel harness connectors. Also unplug park brake switch connector (hydraulic brakes only) at lever.

B. Remove 2 screws holding alarm module to control island dash panel. Discard alarm module and retain screws.

C. Drill a 25.0 mm hole in control island dash panel and insert fuel pump feed harness (5) through hole from dash side to engine compartment and seat feed harness grommet (Figure 2).

IMPORTANT: All holes drilled in control island must be clear of all components and reinforcement panels.

D. Install new alarm module (1) from service kit with existing screws (Figure 2).

E. Connect fuel pump feed harness connectors (1) as follows (Figure 2):

1. Module connector (3-way female) to module assembly (1).

2. Instrument panel connector (3-way male) to instrument panel harness.

F. Connect remaining module connectors (1) as follows (Figure 2):

1. Instrument panel connector (8-way female) to instrument panel harness.

2. Park brake connector (2-way male) to park brake switch jumper harness (hydraulic brakes only).

3. Tell-tale (8-way) connector to Tell-tale.

G. Install ground wire (16-gauge black) ring terminal as follows:

1. Drill a 5.4 mm hole in control island dash (Figure 2).

2. Clean surface of paint.

3. Screw ground wire down and torque to 3.4 - 4.6 Nm 30-40 lbs/in).

H. Disconnect engine and forward lamp harness connectors (2-way weather packs) and connect fuel pump feed harness 2-way connectors between them (Figure 3).

I. Route fuel pump wire assembly from fuel tank to control island area with the engine harness (Figures 1 and 2).

J. Attach fuel pump wire assembly to existing harness with the 20 band straps provided in the service kit. Space straps approximately 400 mm (16 inches) apart. If there is excess length in wire assembly, tie back excess and band strap to body of existing harness.

K. Attach connector on fuel pump wire assembly (1) to fuel pump harness connector (3) at control island area (Figure 3).

3. FINAL INSPECTION AND TEST

A. Reconnect battery ground cable.

B. Reinstall tank drain plug.

C. Refill tank with fuel and operate pump.

IMPORTANT: To check if in-take fuel pump is operating properly, it will be necessary to disconnect fuel line at tank and check for flow, since mechanical pump is still operational.

D. Check fuel lines and drain plug for leakage.

Parts Information

To make above changes, three (3) parts must be ordered as listed below:

- Fuel tank sender assembly.

- Electric pump assembly.

- Vapour Lock installation kit/electrical harness (based on vehicle RPO content).

Part Number Description Quantity ----------- ----------- -------- 15625359 Installation kit used with either 1 30/60 gallon fuel (Order V.I.P.) tank.

25094477 Sender assembly 60 gallon fuel tank. 1

25094470 Sender assembly 30 gallon fuel tank. 1

25115955 Electric pump assembly (fits both 60 1 and 30 gallon sender)

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.