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What makes engine mifire at all speeds

(1996 Ford F-150)
in Freedom, PA on April 11, 2011
engine has a slight miss every 15 seconds at idle. at all driving speeds the engine misfires badly... changed plugs and fuel filter and added lucas injector additive no help .. the plugs were light gray and burning clean .. no check engine lights ... any ideas ?
Displaying 2 answers & 2 comments
Popular Answer
on April 11, 2011
i would continue and replace the cap, rotor and wires. cover all the basics before going somewhere else. if this does not work, get a diag from a shop with a bid.

thanks for using repairpal.

on April 13, 2011
Thanks Roy, I will do that .. i have dual gas tanks on truck and a co-worker had the same problem and he told me to check cat converter as switching between tanks can clog converter !! I have never heard of that .. I will change all tune up parts before I get into that..
on April 13, 2011
your welcome
on July 29, 2011
if you have two tanks replace the fuel tank switch on the dash fixed mine 13.99
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