General Motors — Fuel Injector Balance Test with Special Tool
Testing & diagnosis · Fuel Injectors
From a General Motors service manual — check it applies to your exact model before use.
Before you start
- Do Not repeat any portion of this test before running the engine in order to prevent the engine from flooding
Procedure
- Connect the J 39021 fuel injector tester to a fuel injector using the J 39021-380 injector test adapter
- Set the amperage supply selector switch to the balance test 0.5-2.5 amp position
- Energize the fuel pump using the scan tool to pressurize the fuel system
- Record the fuel pressure after it stabilizes (1st pressure reading)
- Energize the fuel injector by depressing the Push to Start Test button
- Record the fuel pressure after the gauge needle stops moving (2nd pressure reading)
- Repeat steps 1 through 6 for each fuel injector
- Subtract the 2nd pressure reading from the 1st pressure reading for one fuel injector to obtain the pressure drop value
- Add all individual pressure drop values to obtain total pressure drop
- Divide the total pressure drop by the number of fuel injectors to obtain the average pressure drop
- Retest any fuel injector outside 10 kPa (1.5 psi) of the average; replace faulty fuel injectors
Tools required
- J 39021 Fuel Injector Coil and Balance Tester Amazon
- J 39021-380 Fuel Injector Test Harness Amazon
- J 34730-1A Fuel Pressure Gauge Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Injector pressure drop tolerance: 10 kPa (1.5 psi)
- Fuel pressure: 379-427 kPa (55-62 psi)
Source: General Motors service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.