Sorry if this is an old/duplicate topic. I did a quick search and did not find anything specific to my issue.

I have a 2006 F150 with 105,000 miles on it. Recently, it has developed a misfire that is progressively getting worse. It happens when the truck is in overdrive, with engine RPM between about 1200 to 1800. Cruising at this RPM the truck runs great. If I increase the throttle, I develop a pronounced misfire. Once the truck down shifts out of OD and engine RPM exceeds 2000 RPM the misfire goes away. I have never had the CEL light come on during any of these events.

The truck has the original plugs in it AFIK. I have not changed them.

Any thoughts or ideas? Thanks!

Kevin

 

Thought mine was misfiring when needing to accelerate. Instead pulled codes for tps instead. Going to replace the sensor and see if that was what I thought was the misfire. Could just be the sensor loses where throttle was at before accelerating?

 

kberlen,

Sounds like a COP issue. You might want to do a search for COP troubleshooting and diagnostics. I know that there are several on here.

 

At 105k you are in need of spark plugs. Not saying that is causing the issue, but they should have been changed out at 60k. That being said, a pronounced misfire should throw a code. If you have access to a decent scan tool you could check mode 6 data also.

 

I had that same behavior two times. The first time, it was my spark plugs that needed to be replaced. I think that is in the 75-80K mile range.

The misfires came back at 120K miles. This time it was the coil packs.

When you have the plugs replaced, be mindful of the issue with spark plugs breaking when removed for the first time--

PC

 

Spark plugs are due for replacement at 100k and in some circumstances don't last that long. That's most likely your issue. I would replace them before trying anything else. In my experience the 97-03's had more COP misfires and the 04-08's were usually spark plug related.

 

I doubt is this will help solve the issue stated here but I too had an unusual miss in my 04. And the solution was just a mysterious. For no reason, all of a sudden the engine (5.4) would just develop a major miss. A quick scan told me the miss was detected in cylinder 7. The first time around I did the logical thing and replace the coil on that cylinder. All was fine for several months and about 5000 miles. Then it returned with the same symptoms. This time a new coil did no good and I was confronted with doing the unthinkable. Pull out the plug. As I didn't buy the truck new I had no idea how long since the plugs were looked at. After reading so much about frozen plugs and the pain to remove them, I was thinking somebody probably was confronted with a bad one of these and simply left the old plug in rather than mess with it. Luckily for me it came right out.

Prior to starting I stopped by the local parts store and picked up a new coil and plug. When I removed this plug, the electrode. (single) was completely smashed shut and bent to the side. This was scary! I compared the old plug with the new one and found it to be about a quarter inch longer then the new plug. That was strange, but I installed the new plug and the engine ran better than it ever had for me. No coil needed. How this plug worked for over 15000 miles since I bought the truck is beyond me.

Moral of the story, don't assume that the correct plugs are installed just because it ran well for a time. Maybe somebody can explain how this situation happened. It would be appreciated.

One last thing. Thinking my mileage would improve after finding this, and the fact the engine ran so much better, to my surprise the mileage actually dropped about three tenths mile per gallon.