SERVICE MANUAL UPDATE/FUEL PRESSURE CHECK/INJ. BALANCE
Model and Year: 1988 NOVA SERVICE MANUAL (ST-373-88)
SERVICE MANUAL UPDATE
This bulletin is being written to revise the Fuel Pressure Check Procedure (page 6C-55); and the Injector Balance Test (pages 6C-58 and 6C- 60) of the 1988 Nova service manual.
FUEL PRESSURE CHECK
Before performing the fuel pressure test, check the following components:
* All fuel hoses and connections for kinks, restrictions, or leakage.
* Fuel pressure regulator vacuum sensing hose for kinks, restrictions or leakage.
* Fuel filter for blockage
* Fuel pump for operation
* Battery voltage supply for at least 12 volts.
1. Disconnect the negative battery cable.
2. Place a shop towel around the fuel pressure tap.
3. Slowly loosen the fuel pressure tap to relieve fuel system pressure. system pressure has been released, remove the fuel pressure tap and washer.
4. Install adaptor J37144 into the fuel rail using the fuel pressure tap washer.
5. Connect a fuel pressure gage J34730-1 to the adaptor.
6. Wipe up any gasoline that may have spilled in the engine compartment.
7. Use a length of service wire to jumper the fuel pump check connector. (The fuel pump check connector is located at the right hand strut tower in the engine compartment. The connector can be identified by its brown wire and its red/green wire.
8. Reconnect the negative battery cable.
9. Turn the ignition switch to ON.
10. Measure the fuel pressure.
Fuel pressure should be 265-304 kPa (38-44 psi).
If fuel pressure does not meet specification and fuel lines, pump, and filter were found to be good, replace the fuel pressure regulator.
If fuel pressure meets specification, proceed to Step 11.
11. Remove the length of service wire from the fuel pump check connector.
12. Start the engine and allow the idle to stabilize (about 90 seconds).
13. Measure the fuel pressure at idle.
Fuel pressure should be 206-226 kPa (30-33 psi) .
If fuel pressure does not meet specification and fuel pressure regulator vacuum sensing hose is good, replace the fuel pressure regulator.
14. With the fuel pressure gage still connected, turn the engine OFF. Measure the fuel pressure after the engine has been OFF for five minutes.
Fuel pressure should be above 146 kPa (21 psi).
If fuel pressure does not meet specification, check the injectors and the fuel pump check valve for leakage.
15. Place a shop towel around the fuel pressure tap. Slowly loosen the fuel pressure gage connection to relieve fuel system pressure. Once system pressure has been released, remove the fuel pressure gage, adaptor and washer.
16. Reinstall the fuel pressure tap and washer.
17. Wipe up any gasoline that may have spilled in engine compartment.
18. Start the engine and check for leaks.
INJECTOR BALANCE TEST
The injector balance tester tool is used to energize the injector for a precise time period. Since the injector is energized for a measured period, the amount of fuel sprayed into the intake manifold per each injector ON period is also precisely measured. This causes a drop in fuel rail pressure that can be recorded and compared between each injector. All injectors, when they are individually energized, should cause the same amount of pressure drop. Any injector that causes a pressure drop of more or less than 20 kPa (3.0 psi) from the average is defective and should be replaced.
If engine has been operating, a cool down period of at least ten minutes is necessary to avoid irregular readings due to "hot soak" fuel boiling.
1. Disconnect the negative battery cable.
2. Place a shop towel around the fuel pressure tap.
3. Slowly loosen the fuel pressure tap to relieve fuel system pressure. Once system pressure has been released, remove the fuel pressure tap and washer.
4. Install adaptor J37144 into the fuel rail using the fuel pressure tap washer.
5. Connect a fuel pressure gage J34730-1 to the adaptor.
6. Wipe up any gasoline that may have spilled in the engine compartment.
7. Install a length of service wire to jumper the fuel pump check connector. (The fuel pump check connector is located at the right-hand strut tower in the engine compartment. The connector can be identified by its brown wire and its red/green wire) .
8. Reconnect the negative battery cable.
9. Turn the ignition switch to ON.
10. Insert the clear tubing attached to the gage vent valve into a suitable container. Open the gage vent valve. Bleed any air trapped in the gage or hose to insure accurate readings. Close the gage vent valve.
11. Turn the ignition switch to OFF.
12. Disconnect the harness connectors from all four fuelinjectors.
13. Connect injector tester J34730-3A (included in Test Kit J34730-B) to the number 1 injector. Follow the tester manufacturer's instructions for use of adaptor harness. (When connecting the tester, use the two wire leads which splice off from the connector. DO NOT use the tester's injector connectors - they do not fit the Nova Twin Cam engine fuel injectors).
14. Turn the ignition switch to ON. Allow fuel pressure to stabilize.
15. Turn the ignition switch to OFF.
16. Record the pressure reading.
17. Press the tester's button and energize the fuel injector ONCE. Note and record the pressure drop at its lowest point. (Disregard any pressure increase after the initial drop.)
18. Subtract the second pressure reading (Step 17 from the first reading (Step 16). The difference between the two readings is the actual amount of pressure drop caused by the injector being energized.
19. Disconnect the injector tester leads from the Number 1 injector and connect them to the Number 2 injector. Repeat Steps 14 through 18.
20. Repeat Step 19 for the Number 3 and 4 injectors.
21. Retest any injector that causes a pressure drop of more or less than 20 kPa (3.0 psi) from the average.
* If any injector fails the retest, it is defective and should be replaced.
* If all injectors are within 20 kPa (3.0 psi) of the average pressure drop, the injectors are energizing and opening normally.
22. Reconnect all fuel injector harness connectors.
23. Place a shop towel around the fuel pressure tap. slowly loosen the fuel pressure gage connection to relieve fuel system pressure. Once system pressure has been released, remove the fuel pressure gage, adaptor and washer.
24. Reinstall the fuel pressure tap and washer.
25. Wipe up any gasoline that may have spilled in engine compartment.
26. Start engine and check for leaks.
IMPORTANT
To prevent flooding, do not repeat the injector balance test again unless the engine has been run.
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.
