Symptoms of Bad 7.3 Powerstroke Under Valve Cover Harness

The UVCH is a critical component of the 7.3 Powerstroke’s fuel injector system. For the injectors to fire, they need a bit more power than the batteries themselves can provide. 

When properly maintained, the 7.3 under valve cover harness can provide years of trouble-free service. However, there are several common problems that can develop over time. 

In this very article, let’s learn how to detect when your under valve cover harness needs immediate attention.

What Is The Sign Of Bad 7.3 Powerstroke Under Valve Cover Harness?

Many users have experienced bad UVCH, but they could have prevented the problem if they were aware of the initial sign and symptoms to get a hint. 

The most common and obvious signs of UVCH failure are:

  • Poor performance and rough engine running (usually limited to 1-2 cylinders)
  • Engine misfires
  • Usually no check engine light codes 

Bad 7.3 Powerstroke Under Valve Cover Harness Symptoms

There are other significant symptoms by which you can easily identify when your UVCH needs proper inspection and repairing or replacement. 

So, let’s learn more about those symptoms and how to detect 7.3 under valve cover harness failure –

1. Poor Performance and Rough Engine 

Failed UVCH can cause horrible rough running conditions to the point that the vehicle lopes back. As the injector receives less power than usual, the engine shows dire performance. 

The engine is equipped with an Injector Driver Module or IDM. The IDM receives the signal or voltage from the ECM to fire the injectors and then outputs a voltage high enough for the injectors. 

The engine can also misfire if the oil leaks due to bad UVCH. 

2. Oil Leak

If the UVCH is broken, compressed oil can leak from the cylinder. If it happens frequently, the oil level will go down, and the engine oil light will appear on your dashboard. If it continues, it can severely damage the engine. So contact your mechanic if you ever face it. 

Check them before just replacing them. Unplug one at a time. If the engine dies or almost dies, the harness is good. If unplugging one does not change anything, you found a bad harness. If you can do a buzz test, that will also test the harness.

3. Burning Oil Smell

The leaked oil sometimes falls on the cylinder head, fuel intake, or even on the exhaust pipes, especially when the engine is running.

Those hot components will burn the oil and create a smell. So if you can smell burning oil while driving, do check your engine and why the leak has happened.

4. Dirty Valve Cover

The under valve cover harness, as it suggests, sits under the valve cover. 

Dirty valve covers can indicate UVCH failures.   As the leaked oil collects dirt under the hood, it gets caked on the valve cover or the cylinder head. So while changing oil, check the valve cover, and if you find it dirty, it’s most likely that you have a failed UVCH.

These are the most commonly identified symptoms that indicate the UVCH failure condition. So, if you also own one of the 7.3 Powerstroke engines on your vehicle, make sure to keep them in mind.

What to Do When You Detect Bad 7.3 Under Valve Cover Harness Symptoms?

Whenever you encounter any symptoms indicating that your UVCH may fail or has any damage, make sure to follow the below instructions in order to fix the problem-

Doing an ohms test

Doing an ohms test on the harness without taking off the valve covers is a way to keep checking your UVCH.

Unplug the plug going into the valve cover. When you look into the plug in the head, you will see 9 little pins in there, with the 2 outside pins on each side being bigger than the rest. Those pins control as followed –

  •  Glow Plug
  •  Glow Plug
  •  Injector
  •  Injector
  •  Injector common
  •  Injector
  •  Injector
  •  Glow Plug
  •  Glow Plug

If you take a multimeter and do an ohms test with these pins, you can tell if something is wrong.

Go from the injector common to the 4 injector pins, and they should be under 5 OHMS. If they are higher, you might have a problem with the harness.

To check the glow plugs, you put one lead from your multimeter on the glow plug pin and the other one on battery ground. These should come in at 0.6 to 2.0 ohms.

So, you can check the glow plugs with an ohmmeter – Either by directly touching the end of the glow plug with one lead and placing the other on battery ground or by removing the plug at the valve cover and checking the pins in the connector.

You can do this if you test the front 2 and rear 2 pins in the pass-through connector in the valve cover against battery ground. A reading of fewer than 2 ohms indicates a good glow plug.

Is Replacing A 7.3 Under Valve Cover Harness Typically Expensive?

The issue is commonly isolated to certain cylinders as one cylinder’s UVCH connection can fail while the others remain intact. There is one wire on each side of the engine, and fortunately, it’s a pretty inexpensive repair.

When Under Valve Cover Harness (UVCH) Connectors come loose or get shorted, they can cause rough running conditions to the point where the track sounds like it has 17* timing, and it lopes bad and will often die and sputter. 

Since these are under the valve cover, it’s a good idea to replace the valve cover gaskets. The entire valve cover gasket kit with connectors can be replaced for $100 or less.

Final Thoughts

The UVCH is an electrical connector that transfers the voltage from the IDM to the injectors.

The heat of the valve cover and the constant shaking of the engine can cause its wires to melt or break, and it surely has some impacts. Keep in mind the symptoms and solutions that I have mentioned earlier.

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