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If a 6.0L equipped F-Super Duty or an Econoline van exhibits these symptoms first follow normal diagnostic
procedures. The check engine light does not typically come on with this type of harness failure. If the other
concerns that short VPWR to ground that cause the PCM or FICM to shut down are eliminated as possible causes
pay close attention to the fuel injector harness. There are chafing issues that cause injector circuits to
short to ground instantly shutting down the engine like turning off the ignition. Checking the harness visually
is only the beginning as the damage can lie well hidden inside the loom under the tape and convolute tubing.
Look at the top photo and observe the harness laying on an intake manifold bolt. At first inspection the
harness looked okay and there was nothing pressing down on it.
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Closer inspection revealed an imprint of the raised edges of the bolt on the underside. This harness was
removed from the engine and cut open to reveal a shorted injector wire for cylinder number 7. There is one
other thing you need to take notice of in the second photo besides the damaged wire and that is the bare ground
wire that is wrapped around the bundle of wires and then wrapped in the shielding. It has been found that this
bare wire can also cut into the wiring and have the same affect. It is recommended that in checking this
harness that the technician squeeze the harness gently with pliers or use a 1/2" round wooden dowel to
press on the harness while the engine is running. This has proven to be an effective method of discovering
hidden harness shorts in the fuel injection system.
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The second and one of the oldest issues has been with where the harness connects to the FICM. The FICM has
three electrical connections, one being the engine sensor and body connector and the other two are for the fuel
injector harness. Due to it's position on the engine, electrical connections are on the bottom of the
module and the wiring tends to drape down over the left valve cover lip and one of the valve cover bolts.
Eventually the bolts wear through the harness and the result is a grounded circuit. Grounding an injector
circuit generally causes the engine to abruptly shut off. As of early 2005 a new service harness began
appearing when ordering a new harness. New, meaning that it has apparently been redesigned to protect the
wiring better.
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Let's compare the old and the new wiring assemblies. On the left is the factory harness that was removed
and found to have internal short circuits to ground. On the right is the new harness installed to replace the
damaged harness. Note the new cover on the back of the connectors that now force the wiring at a right angle
keeping the harness off the valve cover and bolt under the FICM. There also appears to be thicker wrapping in
specific areas and additional retention straps intended to hold the harness to a stud bolt instead of just
resting on top of bolts. This is definitely a step in the right direction. As for the internal issues with the
harness we do not know if the bare ground wire has been eliminated. We did not want to destroy a new harness
that was to be installed on a vehicle. We hope this article will help in diagnosing those vehicles that just
shut off randomly leaving no clues behind eluding a technicians best efforts.
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Some final thoughts and advice to any technician working on these engines:
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Whether you are performing an electrical or driveability repair or just changing the FEAD belt, be
observant and take note of any potential problems with the harnesses.
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Look for harness crushing, chafing and routing that will cause damage. Use a wooden dowel to lightly press
and move the harness while performing a wiggle test. It is also recommended that you gently squeeze the
harnesses with a pair of pliers which will help identify internal harness shorts.
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Whether you repair or replace a harness, pay extra attention to correct routing and commonly known areas
where chafing has caused problems. Add electrical tape and add convolute harness wrapping to further
protect wiring.
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Taking the extra time and effort will pay off for both you and your customer in the long run. If you can
eliminate the possibility of any driveability or no start conditions related to the harnesses on this
diesel engine, you will have saved your customers and yourself from future headaches.
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