All of the fuel system tests will require operation of the fuel pump to measure pressure, evaluate pressure decay, or perform the pressure at calibrated flow tests.
Although the fuel pump can be controlled with the ignition, this is fairly awkward for the following reasons:
Once the fuel pump is commanded ON with the scan tool, it will be energized
for 1 minute before it times out and returns to the OFF status. Do not leave
the vehicle unattended while running any of the system tests with the pump ON.Important
The scan tool provides control of the fuel pump at the technician's finger-tips. The tool will run the pump for 1 minute after the ON command. This timer will then shut the pump OFF.
The fuel system tests outlined in the fuel system diagnostic flow chart and detailed procedures, Tests 1-9, provide a systematic approach to determining whether the fuel system, from fuel pump to the fuel injectors, is functioning as intended.
For the engine to operate as designed, the fuel supply system must do the following:
In addition, the fuel injectors must deliver the precise quantity of fuel at exactly the correct intervals with no leakage of fuel when the injector is turned OFF.
The battery of tests outlined in the Fuel Supply Diagnosis flow chart are designed to evaluate all the performance characteristics. Symptoms or complaints related to the fuel system include:
Diagnostic trouble codes associated with fuel supply problems include DTC P0171 and P0172.
The performance of the fuel pump (pressure and flow) is very dependent on supply
voltage. The voltage must be above 12 volts when running any of the diagnostic
tests. Published test specifications cover the range of system operation from 12-14 volts,
but are biased towards the lower voltages (12-12.7 volts) since all
tests are run with the engine OFF. All accessory loads should be off when running
any tests (DRLs, interior lights, radio, etc.) to provide maximum available voltage
for the tests. If voltage is below 12 volts, the battery must be charged
before running tests.Important
Fuel Pump Operational Test -- Test to establish whether fuel pump is operating and providing fuel to the injectors.
Fuel System Pressure Test, at idle or engine OFF -- Tests the basic integrity of the fuel system to determine whether regulated operating pressure is achieved under low load conditions.
Fuel Pump Flow/Pressure Tests -- Tests to determine if the fuel pressure is within operating limits while simulating the flow demand of the engine running at wide open throttle. These tests are run with the engine OFF and provide a means, based on testing at 2 points in the system, of determining if the fuel filter/pressure regulator and fuel pump are operating to design specifications.
The testing is performed using the SA9127E-7 Fuel Flow/Pressure Adapter which incorporates a precision orifice to meter 50 liters/hr (13 gallons/hr) at a delivery pressure of 330 kPa (48 psi).
The flow/pressure adapter consists of the following:
It is connected with the inlet side (1) to the fuel feed, either at the fuel rail or at the filter/pressure regulator inlet, the outlet (5) to fuel return (or drain), and the gage port (2) to the pressure gage. The ON/OFF control valve (4) provides a means to control fuel flow for pressure and leakdown testing.
The test criteria is the fuel pressure read while the fuel pump is energized with the engine OFF. Refer to Energizing the Fuel Pump. If the pressure measured is within specification, then the fuel supply is capable of meeting all volume requirements of the engine.
Fuel System Pressure Leakdown, Decay - These tests determine if the fuel system will maintain pressure after the engine, and fuel pump, are shut OFF. Fuel pressure must be maintained after shut OFF to ensure quick restarts and prevent fuel vapor from forming at the fuel rail, causing hard or extended cranks. The tests are arranged to allow isolation of the problem components or area by evaluating components in sequence.
Fuel Injectors Tip Leakage Test - This test determines if the fuel injectors are leaking fuel into the intake system. Leaking fuel injectors can cause problems with extended cranks, hard starting, and rich running conditions, DTC P0172.
Fuel Injector Balance Test - This test determines if the fuel injectors are metering an equal quantity of fuel when they are commanded open. By measuring the fuel pressure drop during a timed cycle of opening each injector, a relative evaluation of each injector's flow rate is made. This test is designed to identify injectors with significant differences in flow rate but will not identify problems with an injector flow pattern, i.e., improperly sized spray cone, non-uniform spray cone pattern, mis-directed spray cone, etc.
If the vehicle is not operating or will not start or run, then a determination must be made if the fuel pump is working and fuel under pressure is being delivered to the fuel rail.
Do not allow smoking or the use of open flames in the area where work on the
fuel or EVAP system is taking place. Anytime work is being done on the
fuel system, disconnect the negative battery cable, except for those tests where battery
voltage is required.Caution
Whenever fuel line fittings are loosened or removed, wrap a shop cloth around
the fitting and have an approved container available to collect any fuel.Caution
This test will determine whether there is adequate fuel pressure delivered to the fuel injectors to start and run the engine under low load conditions.
Do not allow smoking or the use of open flames in the area where work on the
fuel or EVAP system is taking place. Anytime work is being done on the
fuel system, disconnect the negative battery cable, except for those tests where battery
voltage is required.Caution
Battery must be at a minimum of 12 volts when performing any fuel system
test. Charge battery before proceeding if below 12 volts.Important
These tests will determine whether the fuel system can supply adequate volume of fuel at the desired pressure to operate the engine under full load conditions. The test is done at 2 points in the system, fuel rail and fuel pump, to isolate and identify the problem component: fuel pump, filter pressure regulator, or fuel supply line.
Do not allow smoking or the use of open flames in the area where work on the
fuel or EVAP system is taking place. Anytime work is being done on the
fuel system, disconnect the negative battery cable, except for those tests where battery
voltage is required.Caution
Battery must be at a minimum of 12 volts when performing any fuel system
test. Charge the battery before proceeding if below 12 volts.Important
Whenever fuel line fittings are loosened or removed, wrap a shop cloth around
the fitting and have an approved container available to collect any fuel.Caution
To properly utilize the fuel flow/pressure test adapter, it must always be connected
with the fuel feed line on the INLET. The inlet side is the side of the adapter and
the fuel return or drain line connected to the side with the flow control (ON/OFF)
valve. If not connected properly, a zero pressure reading will always
be read. Use the appropriately sized connector fittings to hook up the adapter to
the feed and return lines.Notice
The battery must be at a minimum of 12 volts when performing any fuel
system test.Important
For this test, the vehicle will be raised on the hoist and a means of controlling the fuel pump from under the vehicle is required. The scan tool readily provides this function. Refer to Energizing the Fuel Pump.
Do not allow smoking or the use of open flames in the area where work on the
fuel or EVAP system is taking place. Anytime work is being done on the
fuel system, disconnect the negative battery cable, except for those tests where battery
voltage is required.Caution
The battery must be at a minimum of 12 volts when performing any fuel
system test. Charge battery before proceeding if below 12 volts.Important
Whenever fuel line fittings are loosened or removed, wrap a shop cloth around
the fitting and have an approved container available to collect any fuel.Caution
To properly utilize the fuel flow/pressure test adapter, it must always be connected
with the fuel feed line on the INLET. The inlet side is the side of the adapter and
the fuel return or drain line connected to the side with the flow control (ON/OFF)
valve. If not connected properly, a zero pressure reading will always
be read. Use the appropriately sized connector fittings to hook up the adapter to
the feed and return lines.Notice
The fuel system leakdown test will determine if the fuel system is able to hold fuel pressure when the fuel pump is not operating. The system must hold pressure to assure that the fuel supply circuit, fuel lines, filter/regulator, and fuel rail, is full of fuel. When the fuel supply is completely charged, fuel will be available at the injectors as soon as the ignition is turned ON.
Do not allow smoking or the use of open flames in the area where work on the
fuel or EVAP system is taking place. Anytime work is being done on the
fuel system, disconnect the negative battery cable, except for those tests where battery
voltage is required.Caution
Whenever fuel line fittings are loosened or removed, wrap a shop cloth around
the fitting and have an approved container available to collect any fuel.Caution
The battery must be at a minimum of 12 volts when performing any fuel
system test. Charge battery before proceeding if below 12 volts.Important
This test will determine if the fuel supply system, up to the fuel rail and injectors, will maintain pressure after the fuel pump is turned off.
Do not allow smoking or the use of open flames in the area where work on the
fuel or EVAP system is taking place. Anytime work is being done on the
fuel system, disconnect the negative battery cable, except for those tests where battery
voltage is required.Caution
This test can be performed using the
J 37287-100
Fuel Line Shut Off Quick Connect Adapter.Important
The battery must be at a minimum of 12 volts when performing any fuel
system test. Charge battery before proceeding if below 12 volts.Important
Whenever fuel line fittings are loosened or removed, wrap a shop cloth around
the fitting and have an approved container available to collect any fuel.Caution
To properly utilize the fuel flow/pressure test adapter, it must always be connected
with the fuel feed line on the INLET. The inlet side is the side of the adapter and
the fuel return or drain line connected to the side with the flow control (ON/OFF)
valve. If not connected properly, a zero pressure reading will always
be read. Use the appropriately sized connector fittings to hook up the adapter to
the feed and return lines.Notice
This test will determine if the fuel pump will maintain pressure after the pump is turned OFF.
For this test, the vehicle will be raised on the hoist and a means of controlling the fuel pump from under the vehicle is required. The scan tool readily provides this function. Refer to Energizing the Fuel Pump.
Do not allow smoking or the use of open flames in the area where work on the
fuel or EVAP system is taking place. Anytime work is being done on the
fuel system, disconnect the negative battery cable, except for those tests where battery
voltage is required.Caution
The battery must be at a minimum of 12 volts when performing any fuel
system test. Charge battery before proceeding if below 12 volts.Important
Fuel supply lines will remain pressurized for long periods of time after the
engine is shutdown. This pressure must be relieved before servicing the fuel system.Caution
Whenever fuel line fittings are loosened or removed, wrap a shop cloth around
the fitting and have an approved container available to collect any fuel.Caution
To properly utilize the fuel flow/pressure test adapter, it must always be connected
with the fuel feed line on the INLET. The inlet side is the side of the adapter and
the fuel return or drain line connected to the side with the flow control (ON/OFF)
valve. If not connected properly, a zero pressure reading will always
be read. Use the appropriately sized connector fittings to hook up the adapter to
the feed and return lines.Notice
Do not allow smoking or the use of open flames in the area where work on the
fuel or EVAP system is taking place. Anytime work is being done on the
fuel system, disconnect the negative battery cable, except for those tests where battery
voltage is required.Caution
Whenever fuel line fittings are loosened or removed, wrap a shop cloth around
the fitting and have an approved container available to collect any fuel.Caution
Lay shop towels on the intake manifold and cam cover to collect
any fuel.Caution
Make sure the injectors are positioned to prevent fuel from being sprayed onto
the engine. Make sure that the injector retaining clips are properly installed.Caution
The battery must be at a minimum of 12 volts when performing any fuel
system test. Charge battery before proceeding if below 12 volts.Important
The pressure gage reading should be approximately 276-379 kPa (40-55 psi).Important
Do not allow smoking or the use of open flames in the area where work on the
fuel or EVAP system is taking place. Anytime work is being done on the
fuel system, disconnect the negative battery cable, except for those tests where battery
voltage is required.Caution
If the engine is at operating temperature, allow a 10-minute cool down
period.Important
Whenever fuel line fittings are loosened or removed, wrap a shop cloth around
the fitting and have an approved container available to collect any fuel.Caution
It may be necessary to cycle the key ON/OFF a minimum of 3 times to bleed
all air from the system and achieve maximum system pressure. The key must be OFF
30 seconds.Important
The engine must be started after four cylinders have been tested to prevent
flooding or internal damage.Notice
EXAMPLE | ||||
Cylinder | 1 | 2 | 3 | 4 |
1st Reading (psi) | 45 | 45 | 45 | 45 |
2nd Reading (psi) | 40 | 42 | 44 | 42 |
Average of 2nd readings (psi) | 42 | 42 | 42 | 42 |
Difference (2nd Reading - Avg of 2nd Readings) | -2 | 0 | 2 | 0 |
Allowable Difference -- +/- 1.5 psi (10 kPa) | ||||
Cylinder #1 is faulty (rich) or too much drop. Cylinder #3 is faulty (lean) or not enough drop. | ||||