I have a 2001 F150. It has the 5.4L V8. 215,000 miles. I have a misfire on cylinder #1. I took it to the mechanic. The first time he replaced the coil and plug that connects to the coil. I picked it up and immediately had the same issue. I brought it back and the connector pins pushed out the back of the plug. He said it was a bad plug and warrantied the part and labor. I drove it about 500 miles in 3 months and the misfire is happening again. Should I try a different shop? Anyone have similar issues? The plugs are new. Thanks for your help.
Many things can cause misfires aside from coils and plugs. See the troubleshooting section of the FAQ.
Should I try a different shop?
While 3 months can seem like a long time to many mechanics, you only went 500 miles and that's nothing.
We have no way of knowing what diagnostics he may have or may not have performed. We don't know if this mechanic used OEM parts. There's just too little information to condemn this mechanic's work at this point. Old plastic connectors can break on any mechanic - if he fixed that I'd personally give him another shot.
A bad ground connection for the spark plug will damage ignition coils. That's one of the reasons spark plug manufacturers don't recommend using anti-seize on spark plug threads, because it interferes with the ground connection between the threads and the engine block. The other reason is the grease throws off torque specs.
Carbon tracking down the side of the ceramic coating of the spark plug or the ignition coil boot causes high electrical resistance and causes misfires. That's why it's recommended to coat the inside of the ignition coil boot with dielectric grease to prevent carbon tracking from occuring.
2001 F150 5.4L 215,00 miles. I have had this truck 4 years. I've put very little miles on since I bought. I've put just about 15,000 miles. I have worked on it and 2 different mechanics. The truck has had 7 total coils put on the #1 cylinder and new plug for the coil. The truck keeps eating the coils. The mechanics verified compression is good on the cylinder. We have tried aftermarket and OEM coils. After a couple hundred miles the misfire starts again. It's again a bad coil. Does anyone know what can cause this? I'm sceptical to try another mechanic. They always find it's a bad coil and replace it. Then I drive some miles and it's bad again. Thanks for your help.