I have a 98 5.4 and i read the computer and it said number 4 misfire well i replaced the cop for #4 and then i got a new code with a faulty circuit misfire for #4, so i replaced the lead for the #4. So now it has the power that was missing but still get the studdering at higher speeds but no engine light. Is it another cop or a fowled plug? If so how can i check the cops with an engine light coming on?

 

aa767man

A misfire code does not automatically indicate a bad COP---just helps to narrow down the variables to diagnose. Did you test the COP to see if it was bad using an ohmmeter to check the primary and secondary resistance? Also, did you inspect the boot between the COP and the plug to see if there were any cracks or breaks that could allow the secondary to ground? Did you inspect the plug to see if it was fouled or worn? Did you clear the codes after your COP change?

To answer your question about a different COP, the stored code identifies the cylinder where the misfire is detected. For example, P0304 would be cylinder/COP #4, which is last one in the back, passenger side.

Hope this helps.

 

I ended up just replacing the COP. But the original code i got was a po359 or circuit fault cyl #4 misfire. I did not have the tooling to get the plug out. As with the last 6 cops i have changed the truck ran like it was a COP so i changed it. Do you have to pull out the cop to check ohms?

 

if your plugs have over 50k then replace them. I have been down this exact road with my own and two different friends with Expeditions.

 

if u think you need to replace the COP you might as well replace the plug and boot while your there............a misfire could mean a bad plug or boot

MY 5.4 has had the #4 and #7 cyn codes
its easier to just replace the COP plug and boot all at the same time

I would just get the parts and go to a garage and see if they would put it all in....thats what i do ...labor is usually not more than 30-50 bucks

 

You could probably check the primary with the COP in place, but have to pull it to check the secondary, which requires clipping to the spring in the boot.