2004 5.4L Weird Misfire issue - Ford Forum - Enthusiast Forums for Ford Owners

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Old 03-15-2017, 04:01 PM
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Default 2004 5.4L Weird Misfire issue

Hey guys, hopefully someone on this forum can help me out with this issue.

I recently replaced the plugs in my 2004 F150 5.4L due to 2 badly misfiring cylinders (3 and 8). Once the new plugs were in, the truck ran flawlessly for 2 days. All of a sudden i am now getting a slight misfire every once in a while again going highway speeds. The engine light will flash and the truck will slightly shake. When i let off the gas within 10 seconds the engine light will stop flashing and disappear and the truck is back to full power and running perfect again for a while. I have my ODB Code reader hooked up as i'm driving and it shows me which cylinder had misfired. I clear the code each time i stop the truck.

The issue i am having is that each time it misfires it is telling me it was a different cylinder. In the last 4 days it has threw a code 10 times. 1 misfire on cylinder 3, 4 misfires on cylinder 4, 2 on cylinder 5, 1 on cylinder 6 and 1 on cylinder 8, as well as a "system too lean bank 1" code.

I have to travel 10 miles to work and 10 miles home each day. I usually get a misfire half way to work and the truck loses some power, but the misfire stops within seconds and its back to full power, and usually the same on the way home. Some trips it does not misfire at all and runs great.

Today on my way home from work i got 2 misfires at the same time (cylinder 4 and 6) and the truck shook uncontrollably until the light stopped blinking and all of a sudden BAM, back to full power and no issues again for the rest of the drive home.

Could a fuel issue be causing this problem? Plugged filter or weak fuel pump?

I'm almost certain its not the coils as the misfires are happening randomly and different cylinders each time.

I'm not sure where to begin troubleshooting, any help would be greatly appreciated.
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Old 03-19-2017, 01:42 PM
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I'm having the same issue on my 04. I get misfires where the truck shakes and loses power but then drives fine for the next few days. Codes always read a misfire but different one each time. I had a plugs replace 6 months ago and a few coils. That didn't change anything. This weekend I was driving in the mountains and it shuttered every time it went up a incline. I also sometimes get a faint gas odor when the engine starts. My local ford dealer is the type that just changes parts with really troubleshooting so I'm hesitant to take the truck back there.
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