2006 Ford F-150 5.4L No Code Misfire
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General Information: This F-150 came in with a running rough condition. There were no codes in the truck but it was obvious that it was a misfire that was causing the rough running.
First Thoughts: Generally, misfires do not cause me any fear, but on these particular trucks, it makes me a little anxious. These F-150s with the 5.4L have unique spark plugs that have a unique issue when trying to replace them. These spark plugs are known for breaking in the engine. It is so bad that there is a special tool made specifically for these spark plugs when they break. But the good thing is, it is possible to remove them and not break them. I will explain how later down the article.
Diagnostics: The first step in diagnosing this truck was to try and pull the codes. Of course, from the title, there were no codes to be found. The next step was to see if there were any information in the live data.
Using the misfire counter in the live data of my scan tool, I was able to see that number four cylinder had been misfiring. The above photo was taken right before start up.
After start up, more cylinders were misfiring, but they were not as bad as number four.
From experience, I knew this was from an ignition issue. When looking at misfires to determine whether it is an ignition or fuel issue, take a look at the fuel trims. In most cases, if a fuel injector is malfunctioning, the fuel trims would be very lean (close to 20), but with an ignition misfire from a spark plug or ignition coil, the fuel trims only go up slightly, like in this example.
As you can see, the long term fuel trims on bank one are slightly elevated compared to bank two because of the constant misfire from cylinder four (which is on bank one).
How do I know it is not a compression issue? I did a relative compression test and listened for any irregular sounds from the engine cranking. I did not hear a low compression cylinder on this vehicle.
I ended up doing a simple tune up on this vehicle. Spark plugs and an ignition coil for number four cylinder, which fixed the vehicle.
So, how did I remove the spark plugs without breaking any of them?
All I did was warm the engine up to operating temperature, then took the spark plugs out. The heat from the engine allows the spark plugs to break loose from their threads and unscrew in one piece. In some cases, a spark plug may feel like it is tightening back up even when loosening it. In that case, start screwing it back the other way. It may take a few times back and forth, but it will work its way out. Be careful while the engine is hot, you may get burned.
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