I have an '07 FX4 with the 5.4L engine. It had the 40-55mph shudder problem, so I finally replaced the plugs yesterday. I broke 4 of 8, but the Lisle tool got them out with no problem. I seem to have fixed the shudder problem, but introduced a new problem. It ran fine the first time I drove it after replacing the plugs, but the next time I drove it, the CEL came on and the truck started shuddering and wouldn't accelerate at all. I pulled over for a minute, and then it ran fine back home. I put a code reader on it, and it's a P0303 code, so cylinder 3 misfire. I wasn't getting a code at all before changing the plugs. Is this likely the ignition coil pack on that cylinder? It seems to be an intermittent problem. It runs fine most of the time. Thanks.

 

Did you change the boots?

 

No... only the plugs themselves.

 

switch cops to different cylinder and see if the problem jumps cylinders. Check torque. Die electric grease the boots?

 

Its only $32 to change all 8 boots and springs and free to clean the copper contact in the actual coil with a small file. I do this with every plug change. I would change all 8 boots and springs and clean the contact before replacing a coil. Dont forget a little dielectric grease on those boots where they meet the plug.

 

This is a good suggestion as well. You didn't accidentally pull on the connector wires on #3 did you?

 

I did put dielectric grease on the boots before I reinstalled them. I didn't think to check the wires on the connectors though. I'll check that tomorrow, and I'll also swap the #3 COP to a different cylinder to see if the problem moves. Thanks for the suggestions.