Crazy Spark Plug Switcharoo

I just purchased a 2001 Ford Focus with 128000 miles on it. It in good condition, not great, but I got it for a steal and so I’m willing to put some work into it.

I go to buy some plugs at Napa. They sell me the XP5364 (reach of 1.0 inches). I pull the first plug out of the engine and it is an XP 1544, with a reach of 0.7 inches. This is a 16 Value engine (it says 16V Zetec on the valve cover) so the XP5364 is spec. But it appears that someone put the wrong plugs into it. It runs pretty well so I’m surprised. Where on the engine should I look for the spark plug specs? I’d like to confirm I won’t have pistons slapping into spark plugs if I put the “correct” XP5364’s into it.

Double check with the parts store, their website, and cross reference with other part numbers to verify what you have. This actually happened to my brother a month or so ago. He got the correct plugs for his Jeep from the parts house, pulled the old ones out and found out someone had installed the wrong ones previously. We both had the same concern about the longer reach of the correct plugs. As long as you can verify they are the correct ones for your engine, go ahead and gap and install them. Use anti-seize on the threads and dielectric grease on the spark plug boots.

What kind of plugs are those? I’m not familiar with those part numbers. For your Focus, I would recommend either Motorcraft (as OE) or Autolite.

16V is 16 valves, 4 per cylinder.

What does your owner’s manual say about which spark plugs to use?

Autolite XP5364 Autolite Iridium XP Plug:

Rock Auto shows the 5364 as replacing the earlier 5344 for your car. The plugs you took out may have been recommended when installed but things are sometimes learned about engines when the are in service and recommendations change.