Changing plugs in a 4.0 from Autolite to NGK | Ford Explorer Forums
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Changing plugs in a 4.0 from Autolite to NGK

F

flathead

Member
Joined
May 29, 2010
Messages
28
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City, State
Michigan
Year, Model & Trim Level
03 XLS 2 door
Changing plugs on a 2006 Explorer 4.0 replacing the original Autolite AP 103's with NGK TR55-1 V-Power plugs that are listed for the engine. Question the NGK's have 3/16 longer threads and electrodes than the Autolites. I went ahead and installed five the 6th only went in part way and stopped pulled the plug and noted that piston was at TDC. I think the piston is hitting the longer plug. (was my main worry) Double checked yes the NGK's are listed for my 4.0. Anyone have this problem?
 



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according to rockauto, i cant find it listed for the 4.0 sohc. where did it say it works?
 
























mystery deepens! The Autolite AP103's that were in it aren't even listed for my 4.0! I had a remanufactured replacement engine installed by a engine shop 80,000 or so miles ago after I bought the truck. it had a bad motor in it when I got it. The AP103's are the plugs that were in it. Wonder what's up?
 






Baffling. Summit, O'Reilly's, and Amazon all show compatible with your 2006 4.0L
As much as I like NGK, most Ford's are known to run best with OE Motorcraft or Autolite plugs. Make sure you check for correct .054" gap.

I'd exchange them for Autolite APP 5143 Double Platinum, XP 5143 Iridium, or Motorcraft SP412 Nickel. Compare side by side with the 2683 plugs before leaving the store. GL
 






If 1 spark plug is hitting a piston, I'd question why it's companion cylinder didn't have that issue?
 






Autolite 103 series were used in many earlier 4.0 SOHC's. Shop probably used the AP103 plugs they already had on hand. They fit, we'll use 'em.

Remanufactured motor may have different cylinder heads if that's possible. I don't know. I believe all the 2006 plugs listed will be too long.

Motorcraft SP-500 Finewire Platinum is the preferred OE plug for earlier SOHC's, and are a direct replacement for the Autolite AP103.
 






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