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  #1  
Old 02-04-2010, 08:46 AM
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Default Engine Misfire

2003 4x4 4.0 liter with 90,000 miles misfires when it is cold and damp outside. My truck has been doing this intermittently but it's getting worse. Whenever the temperature is right around freezing and it's raining or snowing the engine will misfire. It happens above 40 mph, never when driving slow, never when it's below 20 degrees, and never when it's above 40 degrees. There are no codes being thrown and the check engine light does not ever come on. Hooked up the computer with a Ford mechanic and it's happening on all cylinders. Replaced the ignition coil and plug wires with motorcraft parts and the truck is still misfiring. Any ideas?
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  #2  
Old 02-04-2010, 09:03 AM
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I know you said you replaced the coil and plug wires.. what about the plugs themselves?
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  #3  
Old 02-04-2010, 09:30 AM
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Forgot to add that the plugs were replaced earlier this winter too. The problem did not improve after changing the plugs.
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  #4  
Old 02-04-2010, 10:47 AM
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In this order, check and possibly replace the following. All of which are components that have to do with air flow into the engine.

- Air filter
- Intake air temperture sensor
- MAF (clean it)
- Throttle body (clean it)
- Throttle position sensor.
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  #5  
Old 02-04-2010, 04:22 PM
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Based on what you described....sounds primary ignition problem....don't bother with plugs or wires......something on primary side is causing problem.....
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  #6  
Old 02-10-2010, 07:39 PM
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may not be getting enough gas. try changing your fuel filter. it could be clogged. my truck used to have a rough idle and it would run the same way at around 45mph or when its cold outside. i changed the fuel pump and filter and the problem is gone.
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Old 02-10-2010, 08:37 PM
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is it hard to start sometimes?? like motor turns over but takes a bit to fire..... if so its a common problem on a 01 to 03 4.0. the fuel pump gets week and also the fuel rail sometimes has to be changed. that could have something to do with your problem
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  #8  
Old 02-10-2010, 09:15 PM
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maybe a fuel problem like to much water in fuel id try going to a different gas station and getting some fuel line antifreeze
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  #9  
Old 02-11-2010, 07:46 AM
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Thanks for all the suggestions... I brought the truck to Ford and they found oil on the mass air flow sensor from my K&N filter. The mechanic cleaned the sensor and replaced my air filter with a stock one. He suggested not using a K&N because of the oil issues. Not sure if it's because of the location of the maf sensor or what... but I've used K&N filters on my vehicles for the last 10 years and I've never had an oil problem before. I'll update the post with the results.
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  #10  
Old 02-11-2010, 08:46 AM
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You're better off with the regular filter anyway. The K&N filter is useless to begin with and if you over oil it, you get what you just saw happen. Don't waste your money on those stupid things.
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  #11  
Old 02-11-2010, 01:27 PM
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i have a k&n filter on mine and it also contributed to the problem. i still run the filter, just dont over oil it.
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