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Old 08-30-2014, 01:28 PM   #1
eastexsteve
 
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Default Has Motorcraft changed plug specs?

I do a lot of driving in my 2012 v6, and it's time for mew plugs at 106k miles. I bought a batch of Motorcraft SP-520 spark plugs (stock plug) and proceeded to check the gaps. I do this by habit on ANY plug I buy, and I do it ever so carefully since they are platinum/iridium plugs. I do not go as far as to change the gaps, as I have never had to. Call it luck, but every pre-gapped plug I have ever encountered were gapped to specs. I just very tenderly check the gaps with a circular gap gauge.

Surprise! These plugs are not .050 - they are .054! Thinking I just made a mistake, I checked the gap gauge with a 1" micrometer. OK there. I then checked the pre-gapped NGK plugs that go in my wife's car. They were dead-on according to the gauge. I even went back up to the parts house and checked a few other pre-gapped plugs. All dead-on. I even checked another box of SP-520s the parts guy had on the shelf. They were also .054 and not .050 as advertised specs claim.

The only thing I can figure is that Ford/Motorcraft has changed the specs on the gap for these plugs. I also find it an odd coincidence that the Autolite XP5363 plugs for this application are gapped at .054.
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Old 08-30-2014, 02:06 PM   #2
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Let us know what you find out, and if you have any problems taking the old ones out.
I've got a ways to go before I change mine, I am interested in seeing how it goes for you.
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Old 08-30-2014, 02:35 PM   #3
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Gap specs are .049-053 in the 2011 Mustang shop manual for the SP-520. Like you, I checked the gaps on my plugs before I changed them this morning, and they were all gapped at .052. Strange. I got my plugs from Rock Auto, not that it should make a difference in pre-gapped specs.

After the plug change; I crossed my fingers; started right up and now has a nice smooth idle. Will take it out later for quick run.
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Old 08-31-2014, 12:33 PM   #4
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Quote:
Originally Posted by 1DrunkCat View Post
Gap specs are .049-053 in the 2011 Mustang shop manual for the SP-520. Like you, I checked the gaps on my plugs before I changed them this morning, and they were all gapped at .052. Strange. I got my plugs from Rock Auto, not that it should make a difference in pre-gapped specs.
I don't think it makes a dimes worth of difference between .050 and .054 in the plug gaps on the plugs in these cars, as long as they are uniformly the same gap. But, it does say clearly on the box not to change the gap on these plugs. That's why I'm wondering if Ford/Motorcraft changed the gap specs for these plugs. I'm hoping that if anyone has heard this, they will post here. I just find it strange that these were gapped the same as the Autolite plugs for this car.
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Old 09-02-2014, 07:34 PM   #5
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OK, I changed out the plugs this morning. Had no problems, but I was careful and took my time deciding what needs to come apart and what doesn't. I didn't unbolt the throttle body from the plenum. Instead, I loosened the big hose clamp from the front of the throttle body and took it loose from the intake hose. Make sure you use an air hose or vacuum cleaner and get rid of all the crap along the sides of the intake plenum before you lift it off the engine. I think the trick to not tearing up the plug boots is to not immediately pull the boot/coil straight out, but twist it back and forth gently until you feel that it is no longer stuck to the plug. Use a little dielectric grease on the inside of the plug boot in the appropriate places when going back together.

My car is running the SCT 93 race tune and had 106k (mainly hwy) miles on it. I can't tell any performance increases from the new plugs with the butt dyno. But, I'm definitely seeing at least 2 more miles per gallon.
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Old 09-02-2014, 11:19 PM   #6
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Cool!!
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Old 09-02-2014, 11:19 PM
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