Service Information

Spark

Fuel Injector Diagnosis with Special Tool

Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	Review Strategy Based Diagnosis for an overview of the diagnostic approach.

•	Diagnostic Procedure Instructions provides an overview of each diagnostic category.

The control module enables the appropriate fuel injector pulse for each cylinder. The ignition voltage is supplied directly to the fuel injectors. The control module controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high or too low will affect the engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.

When performing the fuel injector balance test, the scan tool is first used to energise the fuel pump relay. The fuel injector tester or the scan tool is then used to pulse each injector for a precise amount of time, allowing a measured amount of the fuel to be injected. This causes a drop in the system fuel pressure that can be recorded and used to compare each injector.

Diagnostic Aids

•	Operating the vehicle over a wide temperature range may help isolate the fuel injector that is causing the condition.

•	Perform the fuel injector coil test within the conditions of the customers concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.

Reference Information

Schematic Reference

Engine Controls Schematics : Siemens ECM - LPG with LCP → Siemens ECM - Gas without FX3 or LCP → Delphi ECM - FX3

Connector End View Reference

Component Connector End Views

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Special Tools

•	CH -48027 Digital Pressure Gauge

•	J 39021 Fuel Injector Coil and Balance Tester

For equivalent regional tools, refer to Special Tools .

Component Testing

Fuel Injector Coil Test

Verify the resistance of each fuel injector with one of the following methods:

•	If the B34A engine coolant temperature sensor 1 is between 10-32°C (50-90°F), the resistance of each fuel injector should be 11-14 Ω.

⇒	If the injectors measure OK, perform the fuel injector balance test/fuel pressure test.

⇒	If not within the specified range, replace the fuel injector.

•	If the B34A Engine Coolant Temperature Sensor 1 is not between 10-32°C (50-90°F), measure and record the resistance of each fuel injector with a DMM. Subtract the lowest resistance value from the highest resistance value. The result obtained should be equal to or less than 3 Ω.

⇒

If the difference is more than 3 Ω, add up all of the fuel injector resistance values to obtain a total resistance value. Divide the total resistance value by the number of fuel injectors to obtain an average resistance value. Subtract the lowest individual fuel injector resistance value from the average resistance value. Compute the difference between the highest individual fuel injector resistance value and the average resistance value. Replace the fuel injector that displays the greatest difference above or below the average.

Fuel Injector Balance Test with Special Tool (Example)

Cylinder	1	2	3	4
First Reading	290 kPa (42 psi)	290 kPa (42 psi)	290 kPa (42 psi)	290 kPa (42 psi)
Second Reading	186 kPa (27 psi)	165 kPa (24 psi)	179 kPa (26 psi)	200 kPa (29 psi)
Amount of Drop	103 kPa (15 psi)	124 kPa (18 psi)	110 kPa (16 psi)	90 kPa (13 psi)
Average Range: 156-176 kPa (22.5-25.5 psi)	Injector OK	Fuel Injector - Too Much Pressure Drop	Injector OK	Faulty Injector - Too Little Pressure Drop

Ignition ON, verify the scan tool engine coolant temperature (ECT) parameter is less than 94°C (201°F).

⇒	If greater than the specified value, allow the engine to cool before proceeding.

Ignition OFF, install the fuel pressure gauge. Refer to Fuel Pressure Gauge Installation and Removal .
Ignition ON, verify the fuel pressure is within 384-425 kPa (56-62 psi).

⇒	If not within the specified range, refer to Fuel System Diagnosis for further diagnosis of the fuel system.

Observe the fuel pressure gauge for 1 minute. Verify the fuel pressure does not drop more than 34 kPa (5 psi).

⇒	If greater than the specified range, refer to Fuel System Diagnosis for further diagnosis of the fuel system.

Connect the J 39021 tester to a fuel injector with the amperage supply selector switch on the fuel injector tester to the Balance Test 0.5-2.5 amp position.
Command the fuel pump relay ON with a scan tool and record the fuel pressure indicated by the fuel pressure gage after the fuel pressure stabilizes. This is the first pressure reading.

Note:

•	Repeat this step for each fuel injector in order to obtain a pressure drop value for each fuel injector.

•	The fuel pressure may rise after the fuel injector stops pulsing. Record the fuel pressure value immediately after the fuel injector stops pulsing. DO NOT record the higher fuel pressure value.

Energise the fuel injector by depressing the Push To Start Test button on the fuel injector tester. Record the fuel pressure indicated by the fuel pressure gauge after the fuel injector has stopped pulsing. This is the second pressure reading.
Add all of the individual pressure drop values in order to calculate the total pressure drop. Divide the total pressure drop by the number of fuel injectors in order to calculate the average pressure drop. The difference between any individual pressure drop and the average pressure drop should not be more than 20 kPa (3 psi).

⇒	If greater than the specified range, replace the fuel injector.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fuel Injector Replacement