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Fuel Injection Diagnosis in the Pentastar V6
The Pentastar V6 engine uses sequential Multi-Port Electronic Fuel Injection (MPI). This MPI system is computer regulated and provides precise air/fuel ratios for all driving conditions. Fuel is injected into the intake port above the intake valve in precise metered amounts through electrically operated fuel injectors. The Powertrain Control Module (PCM) operates the MPI system and fires the fuel injectors in a specific sequence. Under most operating conditions, the PCM maintains an air fuel ratio of 14.7 parts air to 1 part fuel (by weight) through constant adjustment of injector pulse width (the length of time the injector is open).
The PCM adjusts the injector pulse width by opening and closing the ground path to the injector. Engine RPM (speed) and manifold absolute pressure (air density) are the primary inputs that determine injector pulse width. Figure 1 shows a typical fuel injector.
Fuel Injector Problems
When a problem occurs with a fuel injector, it will probably be noticed by the driver because it will have a negative impact on driveability. It’s comparable to driving with five cylinders instead of six. A number of conditions can cause an injector problem – some mechanical, some electrical.
On many occasions, a Diagnostic Trouble Code (DTC) will be set and stored in the PCM. Using the appropriate scan tool, read all DTC’s and record them on your repair order. Then, check for any DTCs in other modules that can cause a related DTC to be set. With the scan tool, run a Vehicle Scan Report and save the file for future use.
In many cases, a fuel injector problem will be electrical in nature. If there is a problem with the injector circuit, trouble code P0201 will be stored. The last number in the code is the cylinder number. In this case, cylinder 1.
If the code were P0202, the cylinder number would be 2 and so on for each cylinder. Possible causes for this code being set are the following: problems with the connector wiring, control circuit is open/high resistance, control circuit shorted to ground.
With the ignition off, verify that the connector is properly connected to the injector in question. Disconnect the fuel injector harness connector and inspect the wiring and terminals. Also, look for any chafed, pierced, pinched, or partially broken wires and broken, bent, pushed out, or corroded terminals. Repair any of these conditions, as necessary.
A bad injector coil will result in a higher-than-normal resistance reading for the injector. Refer to Figure 2. In order to check the resistance of the injector, connect the adapter, such as GPEC Diagnostic Adapter 10436, to the harness connector terminals. Do not probe the harness connectors. Measure the resistance of the injector.
Note: The resistance varies with the ambient temperature; a higher ambient temperature will yield a higher resistance reading; at 68°F, resistance should be 12 ohms, +/- 0.6 ohms; if the resistance exceeds specifications, replace the injector.
Often, an injector problem will manifest itself as a misfire. The malfunction indicator light (MIL) will illuminate, or flash, depending on the severity of the misfire. A fuel injector that is plugged, or fouled, and spraying excessive fuel, or has an uneven pattern will generally cause a single cylinder misfire; however, if the injector is spraying excessive fuel, that excess fuel could affect adjoining cylinders. In most cases, there will be many more misfire counts on the cylinder with the faulty injector than the adjacent affected cylinders.
The DTC that will be displayed in this case is P0301 in which the last number is the number of the affected cylinder. In this case, cylinder 1 is the affected cylinder. If the code were P0302, the cylinder number would be 2 and so on for each cylinder.
In many cases, but not always, there will be other DTC’s set that indicate an issue with another system other than the fuel injection system. Typically, a multiple cylinder misfire indicates problems with timing, oil or coolant consumption, or air handling. A single cylinder misfire is usually a problem with the fuel injector, ignition coil or spark plug. Perform the necessary diagnostics to pinpoint the exact cause.
Replacing a Fuel Injector
Before replacing any fuel injector, or doing any repair work on the fuel injector system, the fuel pressure in the system must be released. In our example vehicle, the system fuel pressure is generally in the range of 58psi +/- 5 psi. Until the fuel pressure has been properly released, do not attempt to open the fuel system.
A circuit within the Totally Integrated Power Module (TIPM) is used to control the electric fuel pump located within the fuel pump module. Follow these steps to release the fuel pressure: Remove the fuel fill cap. Disconnect the fuel pump module electrical connector. Start and run the engine until it stalls. Attempt to restart the engine until it will no longer run. Turn the ignition key to the off position. Refer to Figure 3. Place a rag or towel below the fuel line quick-connect fitting at the fuel rail ②, then disconnect the fitting.
Remove the air inlet hose, the upper intake manifold and the fuel rail hold down bolts ① (see Figure 3). When removing the fuel supply line from the fuel inlet tube at the fuel rail, care must be taken that the fuel inlet tube is not being over-flexed. Damage to the fuel rail inlet tube may occur.
Remove the fuel injector(s) from the fuel rail, then remove the fuel injector(s) ① from the lower intake manifold ② (see Figure 4). All six fuel injectors are removed from the fuel rail and lower intake manifold in the same manner. If the fuel injector is being replaced, remove and discard both O-ring seals.
Before installing the new fuel injector(s), lightly lubricate the O-ring seals with engine oil. Install the fuel injector(s) into the lower intake manifold. Install the fuel injector(s) to the fuel rail. Install the fuel rail, upper intake manifold and air inlet hose. Re-connect the fuel pump module electrical connector and install the fuel cap. Re-connect the negative battery cable, then start the engine. Finally, check for fuel leaks to ensure that the installation has been done correctly.