I have a 2000 F-150 with about 140000. I keep getting a p0304 code. I have changed the plug twice and the cop. When the engine is completely cool, it runs without the misfire. As soon as I drive it for about a mile, the misfire starts and gets worse. Why misfire when it starts to warm-up?

I would appreciate any suggestions

 

You might have your ECM checked

 

I'vd cleared it twice and the same code keeps coming up after the misfire begins again.

 

Sounds like a bad 02 sensor. Go to Autozone, Advance Auto, Pep Boys, etc, and have them hook your truck up to a code reader. The check engine light has to be on or they say they can't grab the trouble code. They do this free of charge.

 

You may have a base engine concern if you've replaced the plug twice and the coil. Leakdown and compression are where I'd go next.

 

I was wondering if having a different type of plug from the other 7 could perhaps cause such a problem? I did notice that the treads on the new plug were longer than what I pulled off. I went to a second autoparts store to buy the second plug but it was the same--longer threads. The overall plug is the same length.

 

The plug *shouldn't* cause a difference, although I have seen stranger things cause problems. Did you grease up the boot?

 

I am having a similiar issue on my 2000 expy, I had code P0303 I have changed out the plugs and made sure the boots look good. But yet it is still jerky when it gets warm. I can make it jerk but since we have reset the computer after the new plugs it is still giving p1000 so it hasn't completed the test to give us a new code. Any more ideas as to what the issue could be?