My personal car recently developed a randum missfire when I turned on the A/C. Since I had recently replaced the plugs, cap and wires I figuered it must have something to do with the fuel system. I went to my local parts house and got a bottle of fuel injection cleaner and it has taken care of the missfire. If you have a vehicle with 100,000 miles or more, you might consider adding a bottle of fuel injection cleaner.
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I have replaced all 8 coils and spark plugs 1 by 1 in a day, #4 piston continues to mis-fire, i replaced that 1 coil and plug again, still got the same mis-fire, now the truck starts and only stays running if i hold down the gas pedal to about .5 – 1.5 rpm, if i let go the engine stalls out. I’m out of ideas, any suggestions?
It is a 1999 ford expedition  5.4  V8 automatic trans. 2 wheel drive.