7.3L Power Stoke Diesel feel down on power? Does it make funny noises when starting?

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Does your 7.3L Power Stroke Diesel feel like it’s only running on half the motor,  or that it just doesn’t have the towing power it used to?  After checking for codes you may find a code P1316, unfortunately this code is only telling you to check the IDM.  As a diesel owner this is a scary thought….. is it an injector, the IDM failed, or even worse, multiple injectors?  All of these scenarios sound costly and testing the IDM requires a professorial scan tool, that can run a “buzz test”

So, What is a Buzz Test??
This test is a sequence of duty cycles to activate the injectors. This gives the technician the ability to hear a audible tone of the injector pulsing.  This ‘Buzz test’  helps identify if there are any faulty injectors or drivers.

With the 7.3L Power Stroke engine most often this problem is with the Under Valve Cover (UVC) Harness. This is where the wiring passes into the engine to deliver power to the injectors and glow plugs. What seems to be happening is that the natural vibration of the diesel engine is loosening the electrical connection. This gap in the harness connector pins either stops making the connection, or increases the resistance causing the amperage to increase resulting in a burnt up harness connector.

* *Inspect Connector and wiring for any problems

How do you test for this condition without a scan tool?

As the engine is starting, you maybe experiencing a hard start that is accompanied by a distinct sound….
Here is a audio clip of a 7.3L Power Stroke starting up with one UVC Harness not working.

      Misfiring 7.3L Diesel

Doing a temperature test on the exhaust manifold is another way of determining what cylinder(s) are not firing.  This can be done several ways; one way would be to use a inferred temperature gun.  What you are looking for is a temperature difference between the cylinders of the exhaust manifold.  This can also be done by dripping VISINE®  or equivalent  eye drops on the exhaust manifold ports.  When the manifold is cold the eye drops will cling to (stick to and run down) the exhaust manifold.  As the engine warms up the eye drops will start to bounce off.  A correctly firing cylinder will produce enough heat in less than a minute to make it completely bounce off with no trace of liquid on the exhaust manifold. With either test the side not firing will be very slow to heat up.

Once you have determined what side of the engine is the problem, it’s time to pull the valve cover off and inspect the harness connectors.
Tech Tip-  On the drivers side valve cover, there is hidden bolt under the crank case vent.  On the crank case vent, their are 2 o-rings that when removed will not be reusable do to oil saturation or swelling.   DO NOT remove these two bolt holding the vent on, unless you plan on replacing these o-rings.  Use a boxed-end wrench to brake free the bolt and continue to remove bolt using your fingers.

Ford has recognized this problem and has released a connector wedge to resolve the connector from loosening. Part number 2C3Z-14A163-AB

APDTY 726312 
1998-2003 Ford E-Series Vans 2003-1998
1999-2003 F250-550 Super Duty Trucks
2000-2003 Ford Excursion

Dorman 615-202
1995-1997 Ford E-Series Vans
1994-1997 F250-450 Trucks


ASE Certified Technician

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8 Responses

  1. daniel tutor says:

    Would the harness cause exces smoke. With the power loss and hard starts

  2. Eric says:

    I have a 2002 e350 7.3 I used the scangauge2 and everything looks good. Could it be the harness? It is hard to get to the valve covers so I wanted to be sure before I remove them. Is there anything else I should check?

  3. jeff ransom says:

    I just bought a 1997 7.3. When going down the free way it misfires here and there. What could be the problem

  4. Mick says:

    Replaced injectors, glow plugs , head gaskets injector cups… Runs at idle fine. No power when in gear

    • david says:

      I would check the ICP sensor for oil in the connector and then fuel pressure with engine under load. If you have the torque app and elm327 you can monitor ICP (HPOP) pressure too.

  5. Walter W. says:

    I have a 95 f350 7.3 turbo and its really really hard to start and when it does start it has a rough idle and no power in gear. What do you think I should do first? I am at a dead end because I have no code scanner and no engine light. Please help

  6. jayme says:

    For any or all of you GET A SCAN TOOL. I have spent 4000.00 chasing issues without one until I did finally get a used one and now I know I was in the wrong area all along. An auto Enginuity scan tool is 350.00 with the ford bundle. Saave yourself the time and money and get a scan tool.

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