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Old 05-18-2016, 02:15 PM   #1
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Mismatched spark plugs

I ordered some motorcraft sp519 plugs to replace the autolite 5363 plugs and only seven plugs came in the mail. I have zero patience so i replaced 7 of the 8 plugs and would change the 8th when it came in the mail, and now it was stumbling at WOT and i double checked connections and made sure the plugs were torqued. Then being frustrated i put the seven autolite plugs back in and it runs fine now.

Wtf think the sp519 is a hotter plug but i didnt think it would cause it to misfire like that. If anyone can explain this to me it would be very appreciated.
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Old 05-18-2016, 03:01 PM   #2
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Did you gap the plugs before install? Every plug I've seen for these cars varied some in the gap it is set at.
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Old 05-18-2016, 03:09 PM   #3
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Quote:
Originally Posted by 5LHO View Post
Did you gap the plugs before install? Every plug I've seen for these cars varied some in the gap it is set at.
The motorcraft sp519s come pregapped and i also double checked the gap for good measure and did the same with the autolites and everything was at .045
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Old 05-18-2016, 03:24 PM   #4
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Well, the SP519s are a standard heat range plug and the gap you checked should not have posed a problem, as the factory gap is .055. No supercharger on the car, right?

So, I have no explanation other than I've had mixed success with MC plugs over the years. Obviously, it wasn't a great idea not to wait for the 8th plug, as now there is another layer to the puzzle.
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2012 Premium GT, Candy Red, Brembo package, 3.73, MT82, Comfort, Tech, et al. Procal tune, Roush UCA, UMI poly LCA, GT500s, Steeda red bracket, Hoosier 28x10x16 bias drags. Best e/t 11.91 at 115.23 RIP
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Old 05-18-2016, 04:44 PM   #5
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Yes it is NA, and im going to wait for the 8th plug and try again.
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