Fuel Shutoff Solenoid Operation on 6.5L Diesels
The fuel shutoff solenoid is [obviously] responsible for controlling fuel flow to the injection pump. It is a normally closed (off) system, meaning that the spring loaded plunger will close off fuel flow to the injection pump when no power is supplied to the solenoid. When power is supplied to the solenoid, it remains in the open position and fuel will flow freely to the injection pump. However, it is theoretically redundant as the fuel metering solenoid, which is controlled by the PMD, serves the same purpose (thus the reason an engine with a failed PMD will not start). The fuel shutoff solenoid is therefore often considered a backup or failsafe to the fuel metering solenoid; a costly one at that. Nevertheless, an engine will not run with a failed fuel shutoff solenoid as the plunger will restrict fuel flow to the injection pump. Fortunately, testing the fuel shutoff solenoid is not an overly cumbersome task and the replacement ACDelco solenoid available today is an updated version of the original part that addresses previous reliability concerns.
Fuel Shutoff Solenoid Testing
The most common indication of a failed fuel shutoff solenoid is a no start condition. Fuel shutoff solenoid failures can trigger a DTC 13 on 1994/1995 OBD-I vehicles or DTC P0215 on later OBD-II equipped vehicles, but not in all instances. PMD/FSD related problems can easily be mis-diagnosed as a fuel shutoff solenoid problem; always test the solenoid for proper operation.
1) Disconnect the fuel pump from the the chassis wiring harness ( wire connector at frame mounted lift pump) so that it is disabled.
2) Disconnect the fuel shutoff solenoid connector. Probe the electrical connector (engine wiring harness, NOT fuel shutoff solenoid) with a multimeter and measure the voltage across the two connector terminals with the key placed in the "RUN" position (as if to initiate the glow plug pre-heat sequence, do NOT attempt to start or crank engine). A nominal 12 volts (as low as 10 volts if the glow plugs are being cycled "ON" while voltage reading is taken) should be measured across the two connector terminals. If no power is being supplied to the connector, there is a wiring, fuse, or connector problem. If power is being supplied to the connector, proceed to next step.
3) Remove the fuel shutoff solenoid from the injection pump (see procedures in section below) and cover the exposed hole with a clean, lint free shop towel. Reconnect the fuel shutoff solenoid connector to the engine wiring harness. Cycle the key to "RUN" position and observe the solenoid plunger. If the plunger does not travel upwards, the fuel shutoff solenoid is faulty. If the plunger moves, the fuel shutoff solenoid is functioning properly.
A faulty fuel shutoff solenoid is rarely the cause of repeated stalling, hard start, long crank, low power, engine cutting out under load, etc. However, we have experienced instances in which intermittent fuel shutoff solenoid issues were the culprit behind such activity, therefore we suggest you always test the shutoff solenoid when diagnosing such problems so that it can be ruled out.
Fuel Shutoff Replacement Procedures
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• Disconnect both negative battery cables.
• The fuel shutoff solenoid is located at the front of the injection pump, just in front of the upper intake manifold.
• Clean the area around the fuel shutoff solenoid with compressed air to reduce the chance of dust/debris falling into the injection pump when the solenoid is removed.
• Locate and unplug the fuel shutoff solenoid electrical connector. It may be tucked deep below the upper intake manifold, making it difficult to reach.
• Remove the fuel shutoff solenoid by rotating counter-clockwise. There's a nut built into the top of the solenoid that accepts a 1/2 inch or 13 mm socket, making it easier to break loose (it should not be particularly tight).
• Install the supplied o-ring onto the replacement fuel shutoff solenoid. Coat the o-ring with clean engine oil to ensure a positive seal.
• Reinstall the fuel shutoff solenoid by screwing it into the injection pump; install snug, do not overtighten.
• Reconnect the shutoff solenoid electrical connector.
• Reinstall the negative battery cables and test for proper operation. Note that it should not be necessary to bleed the fuel system after replacing the fuel shutoff solenoid.