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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 36088
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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Ford F-250 expert only please.. Code P303 misfire on coil

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Ford F-250 expert only please..Code P303 misfire on coil 3...Techs can't get spark plug out, it turns 3 times then stops, "is mushroomed at the bottom, something possibly knocked it"... turning it enough to get it out will break it enough to break the heads or best case maybe I'll just need a replacement thread kit or Healy coil...Question: What could possibly cause a spark plug to mushroom so that you can't take it out? At first the diagnosis was that the spark plug was put in cockeyed and stripped the thread but they changed the story when I reminded them they were the shop that put those new plugs in two years ago..

Hello. My name is ***** ***** I am happy to assist you today. Give me just a moment to review your post, and I'll be right back with the help you need.

Customer: replied 2 months ago.
Hi Ron


Its no very likely that something smacked the spark plug from inside of the cylinder but more likely it was not installed properly or you have excessive carbon build up on it. What year is this truck and what size engine is this?

Customer: replied 2 months ago.
2001 5.4l v8New long block put in 2011 ( at 170,000 miles)Same spark plug problem in Jan 2015 where they couldn't get it out of number 8 and had to install a new thread kit... all new spark plugs put in two years ago, only 33,000 miles in these plugs
Customer: replied 2 months ago.
However, intake manifold has a leak which threw a P1299 code , slight radiator fluid leak, no overheating issues
Customer: replied 2 months ago.
Nothing is knocking in the engine, it was running pretty smoothly after I put fuel injection cleaners in gas... it was slightly misfiring before the p303 code
Customer: replied 2 months ago.
Different mechanic thought the spark plug might have corroded from the radiator fluid leak , and that's why he couldn't get the spark plug out... brought to ford mechanics and now they told me about the mushroom thing

Well if it will not come out with out force the the options you have is to go ahead and force it out and that usually takes out the threads and then you will need to install a Heli Coil thread repair kit . Usually this is the only damage that will occur as well. The other option would be to pull the head and have a look. I think at this point since this is a fresh engine you should just have them remove the spark plug and do the thread repair kit.

Customer: replied 2 months ago.
I don't mind the thread repair kit... they told me though that it could damage the head getting it out and I'll need to replace that at over $2000 :-(
Customer: replied 2 months ago.
the mushroom story seems unlikely right?

If in fact it just a thread issues with the spark plug then it will not usually damage the head anymore then the threads. The mushroom story seem unlikely because you had no noise before this misfire developed. If in fact it was mushroomed something would have to have come loose and smacked it. I think at this point I would just have them remove it and have a look.

Customer: replied 2 months ago.
My boyfriend knows engines well and he says there's no way anything could have knocked the bottom of the spark plug because the engine is running fine..
Customer: replied 2 months ago.
Thx! I was writing that before I saw your answer...Well, I hope they can just get it out with minor damage to the thread
Customer: replied 2 months ago.
not damage to the head... they said they needed my permission to go full speed ahead in case they damaged the head getting it out :-(

Yea I suspect you will be okay with a thread repair at best. They have to warn you just to cover the Rear ends.

Ron and 6 other Ford Specialists are ready to help you
Customer: replied 2 months ago.
Thx Ron! I'll keep you posted, appreciate the e pert feedback again!
Customer: replied 2 months ago.

Your very welcome and thank you as well. Good luck .

Customer: replied 2 months ago.
Hi again Ron, considering that the "mushroom" thing doesn't seem possible, I realized I shouldn't authorize these Ford mechanics to do anything else to my truck, and I should take it elseswhere, do you agree? I used to take it there for 15 years because I had a friend there... but it's under new ownership now and my friend is in a different department where he can't oversee the work done for me...

I would agree with at if your not comfortable with them. I would at least seek a second opinion .

Customer: replied 2 months ago.
Thank you for replying! Sorry for bother !

No bother at all. Thank you as well.