Friend is getting code for #3 cylinder misfire. 4 months ago it blew the same plug out, fixed it and installed new plug and coil pack and boot. Ran great. Last night he swapped coil pack with another cylinder just to see if
it was the coil pack. At idle it ran smooth but under load motor felt like it was shaking. Any ideas? Thanks.

 

Why did he not look at the plug for an issue?
Is the boot setting on the plug and not jammed off to the side?
There is some reason the cylinder is not firing up to par.
Could even be the injector.
Is there any hissing coming from the plug well while running?
Compression test !
Full trouble shootuing is his friend.

 

There is no hissing when running. Don't know why he didn't pull plug and look at it. He had to work late last night. May go over tonight or this weekend and take a look at it. I was also thinking Fuel injector. Thanks for the reply.

 

My friends truck is running fine now. Problem ended up being #3 Coil pack.

 

I don't mean to hijack the thread....but......lol My 2001 F150 is saying it has a cylinder misfire, and they told me to just get a tune up to fix it. I did that, replaced all the spark plugs etc. It was fine for a couple weeks then went back to shaking when we reached higher speeds and the service engine light came back on. It's back to saying it's a cylinder misfire and the Ford place says it's going to be $150 just to diagnose the darn thing!!! UGH Now the shaking starts at about 35 mph....... Think it could be a coil issue as well?

 

After we read the codes we cleared them. Then we swapped the coil pack from the cylinder that was misfiring to another cylinder. It was fine for a little while and then the Check engine came on. Read the codes and this time the code was for the new cylinder. that is how we came to the conculsion it was the coil pack. We also made sure all coilpack and fuel injector connections had good connections. I would recommend putting dielectric grease on the connections. That was the only thing we didn't do 4 months ago when he blew the plug out of that cylinder. Moisture may have caused that new coil pack to go bad.