F-150 running rough

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  #1  
Old 12-01-09, 02:26 PM
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F-150 running rough

I have a 2001 F-150 quad cab with a 4.6 liter motor. When the truck is at idle it runs fine. When I put it in drive it runs very rough. I tried changing the fuel filter but no dice. When I'm on the road and doing 50 mph or so it runs better. This started on Thanksgiving day, the night before it ran fine.

Any thoughts?

Bill
 
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Old 12-01-09, 04:22 PM
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Could be the EGR valve or the PCV valve. Two of the simplest fixes that would exhibit that behavior without going deeper.
 
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Old 12-01-09, 04:34 PM
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what was the weather like the day and night before this started?

and did you drive through any water shortly before this happened?
 
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Old 12-01-09, 05:05 PM
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Sounds like a coil pack to me.
 
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Old 12-01-09, 07:04 PM
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I was heading there


I would also consider the plug wires suspect. Once the insulation starts breaking down, if they get splashed or even if the humidity soaks them, they can short out.


Typical:

no load (idle), engine is often ok or minimal miss or simply unnoticeable miss.

when you load it (in gear and especially when accelerating) it takes much more current to arc the plug so if the short is the path of least resistance, to ground outside of the cylinder it goes.

then, at 50 and cruise, the HP requirement is greatly reduced. (If I remember correctly, somewhere less than 20 hp to maintain speed on a flat road) so the current needed to arc the plug is again reduce to near a no load requirement and viola` plug arcs and cylinder fires and smoother engine results.

coil can act exactly the same if it is marginally bad, or marginally good.
 
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Old 01-05-10, 03:50 PM
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I forgot I posted this, sorry I never got back to anybody. I took it to the guy I use for inspections for a free code check and it was the coil pack on the number 1 cylinder.

Thanks for the help.

Bill
 
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