Driveability Diagnosis

Injector System Diagnosis- Driveability Issues:

DFI Fuel Pump/Injector Circuit:

NOTE: The injector circuit test should only be performed when the driveability condition is present or when one injector is visually verified to be inoperative. For the injector circuit test to result in a positive diagnosis of an injector circuit fault, the voltage measurements requested by test charts must be taken with the injector fault present.

CIRCUIT DESCRIPTION
The fuel injectors are powered through the 3 amp injector fuses. The Electronic Control Module (ECM) turns on the injectors by applying a ground to ECM P2 connector pins D14 and D16, injector drive circuits. The ECM grounds the injector drive circuits to turn on the fuel injector to supply fuel to the engine. ECM Data Parameter P.0.6, Injector Pulse Width, reflects the time in milli-seconds that the ECM turns on the ground to injector for each injector pulse.

TEST DESCRIPTION
When measuring voltages between ECM red connector pins D14 and Dl6, the voltmeter should read 0.0 volts if the ECM is able to control both fuel injectors to provide equal amounts of fuel. If one injector loses power from the fuse or loses ground from the ECM, the voltage measured between pin D14 and D16 will not be zero, reflecting unequal voltage drops across the injector coils. The voltage reading obtained when an injector fault is present can be used to diagnose injector open to voltage, injector open to ECM, injector coil open or ECM unable to ground the injector drive circuits.

NOTE: To obtain an accurate and useable voltage reading, the essential tool J34029-A DVOM must be used, the DVOM and be set on the 200 VDC scale.

1. DVOM Reads 00.0 Volts: If the DVOM reads 00.0 volts, then both injectors are being powered through the fuses and grounded by the ECM an equal amount; no fault exists at this time.

2. DVOM Reads 00.2 and 02.0 Volts: If the voltage polarity is negative, then injector "B" is inoperative, pin D14 of the ECM red connector is not grounding injector drive circuit 468. The cause is an ECM connector fault or an ECM fault.

If the voltage polarity is positive then injector "A" is inoperative, pin Dl6 of the ECM red connector is not grounding injector drive circuit 467. The cause is an ECM connector fault or an ECM fault.

3. DVOM Reads Above 2.0 Volts: If the DVOM reads above 2.0 volts, then the fault is an open from one of the 3A injector fuses to the ECM. A negative voltage polarity means that an open exists between injector A voltage supply and the ECM--check circuit 481, check injector coil of the injector connected to Blue and Red wires, check circuit 467 for opens or shorts to ground. A positive voltage polarity means that an open exists between injector "B" voltage supply and the ECM - check circuit 482, check injector coil of the injector connected to Green and White wires, check circuit 468 for opens or shorts to ground.