I have had a miss on and off for about a year.Buddy hooked it up to his scanner and had misfires on #3 cylinder. I have a 2001 f150 5.4 with about 120000 miles. I am friends with the guy I got it from at 70000 miles and he bought it at 30000 miles. So I know most history of the truck. So I bought a coil and 8 plugs. When I got to #3 plug I couldn't for the life of me get the socket to go down on the plug. I took screw driver and scraped down there and blew air down the hole and tried pb blaster and blew it out and still couldn't get socket on.Took a picture with my phone of the top of the hole and the top of the plug looked melted or swollen..So I got a socket that didn't have the rubber collar in it and it went on plug finally after about 3 hours. When I got plug out it has what looks like a vacuum line plug over the top of the plug..They look like possibly the factory plugs. Where in the world or why in the world would that be there? No wonder I kept having a miss fire. Anyone have any ideas?

 

A picture is worth a thousand words.

 

My guess is that some where early in its life, they were having misfire issue on #3, either from a bad spark plug or boot and rather then replacing the boot or plug they slid a bit of tube over the spark plug to stop from shorting out and there by stopping the misfire.

How did the #3 spark plug look compared to the rest to the spark plugs?

 

X2. This thread is useless without a picture.

FWIW I have seen people use a piece of vacuum hose or something similar and put the tip of the plug in the end of it and use the hose to work a plug into place in a deep hole so perhaps that's what someone did and for some reason the end of the hose broke off and stayed on the plug.

 

Its not a piece of hose. Its closed at the top like a vacuum line plug.This is the way it came out.

 

Oh yep a picture is better ....I take back my earlier suggestion.

That looks to be probably the rubberized cushion from your sparkplug socket.
IF...that was left on there from the previous repair....you had a miss fire for some time.

 

lol

 

I'd agree that looks like the last person in there left the spark plug socket piece behind

 

I don't agree. All of the socket inserts that I have seen have been an open cell foam and their od is just slightly lager than the id of the socket (so that they're a light press fit into the socket). And I've never seen one that was closed off on the end.

This looks like a cap for a vacuum port but I have No idea how of why it ended up on a spark plug. But I do agree that you would have almost certainly had a misfire the entire time that the plug was installed. Are you sure that your mechanic didn't put this on AFTER he pulled the plug and is pulling your leg?

 

somebody is messing with you. you dont accidentally put a vacuum cap on a spark plug lol.

 

I have seen tricks like that to hide a bad rod bearing.

 

Here's what I found before on a factory truck. Mine was just kinda loosely in the spark plug hole, not perfectly placed over the spark plugs tip.


FWIW the internal socket rubber grips are usually grab the body of the plug just above the hex head part, it's a rubber donut in most cases