Spark plug issues

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Sav_Age2003

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I currently own a 1999 Lincoln Town Car Signature Series, and I have a problem with cylinders misfiring. Every spark plug got changed at 90,000 miles, and I’ve since changed the 3rd and 7th spark plugs. It’s at 93,000 miles now. Does anybody know what could possibly be causing my cylinders to keep misfiring? Lately it’s only been the 7th cylinder
 

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dave42

Senior Member
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Leander, TX C.K.U.
A misfire can be caused by a variety of issues, but if it is a single cylinder, it is often one of three things:
plug, coil, or injector. The only misfires I have had on my '03 so far were coils. Once with very old plugs and once with very new plugs. A common diagnostic technique would be for you to swap out the coils for cylinders 6 and 7 (I would say 7 and 8 but 8 is harder to get to). Then see if the misfire moves to cylinder 6. If so, it was the coil and just needs a new one. If it still misfires on 7, then figure plug or injector. If the plugs are pretty new then I would expect them to be fine, assuming you got the ones Ford specifies.

This explanation is simplisitic, but it often works that way. Good luck.

p.s. If you don't already have your own OBD2 code reader, it is a great tool to have. Mine was about $15.
 

Norms1stTC

Well-known member
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If you can get motorcraft coils, all 8, and motorcraft spark plugs, I'd change them all out . Expensive, but worth it if you're going to keep the vehicle and make it your daily driver. Good luck.
 

Sav_Age2003

New member
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Thank you both of you for the help, i can’t wait for the fix so I can finally drive without the service engine soon light on
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Norms1stTC

Well-known member
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Thank you both of you for the help, i can’t wait for the fix so I can finally drive without the service engine soon light on
Do yourself a favor and source these from trusted sites and make sure they're not counterfeit motorcraft coils and spark plugs , best to source from a Ford/Lincoln dealer if you can, never Ebay , and only a few retailers on Amazon can be trusted. Good luck kid. Have fun and enjoy your new ride. While you're at, pick up a cheap OBD2 scanner to read all your Check engine lights and codes, stored and new. It will help pinpoint what the problem is 99.9% of the time.
 

leishman84

New member
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I currently own a 1999 Lincoln Town Car Signature Series, and I have a problem with cylinders misfiring. Every spark plug got changed at 90,000 miles, and I’ve since changed the 3rd and 7th spark plugs. It’s at 93,000 miles now. Does anybody know what could possibly be causing my cylinders to keep misfiring? Lately it’s only been the 7th cylinder

Did you make sure to gap each of the plugs to .54-.56?
 

Norms1stTC

Well-known member
532
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370
63
Did you make sure to gap each of the plugs to .54-.56?
I think he said in another post it was actually a fuel injector, most , and I say that lightly, most motorcraft plugs should be gapped already from the factory packaging, but it never hurts to check.
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