2002 Ford F-150 F-150 bucks and runs rough

Tiny
DPLOURDE
  • MEMBER
  • 2002 FORD F-150
  • V8
  • 4WD
  • AUTOMATIC
  • 205,000 MILES
I've got an F150 4.6 V8 auto that's running rough but only a small part of the time. I'm NOT getting a check engine light and the problem only seems to come around at about 45MPH and is more pronounced when going up hill at about 45MPH. Does it a little bit at highway speed but not nearly as much. Engine starts and runs fine otherwise. I had the typical coil failure problems a few months ago but that seemed different. It ran bad all the time, gave me a check engine light and a code I could read. Changed some coils and I was all set. I keep expecting the light to come on so I can read the code and change another coil but I don't think it's going to. Injectors? Fuel Pump? Any advice would be helpful.
Thanks.
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Monday, November 2nd, 2009 AT 6:57 PM

2 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
I question if the fuel pump is a concern because it runs good other than that speed. As far as the coild, does your truck have one for each cylender? IF so, I have had similar problems with the actual boot that goes over the spark plug. THey actually arc through them causing spark to short to the engine and some still make it to the plug so you get a mild miss. Have you checked them? If that is the problem, you will see a light gray mark on the boot where it arcs.

If you want to check fuel puressure, here is a how to:

http://www.2carpros.com/how_to/how_to_check_fuel_pressure.htm

You will need a gauge to check it. Most parts stores will lend or rent the gauge.

Let me know what you find.
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Monday, November 2nd, 2009 AT 7:50 PM
Tiny
DPLOURDE
  • MEMBER
I've been thinking more about the rough running on the F150. I don't think it's he coils. The rough running is too predictable to be a bad coil or week boot. I'm thinking it might be a vacuum leak. I can predict exactly when the rough running will start. It happens only at 45MPH at certain power setting (going up hill) when the engine is at certain RPM. When the rough running starts, I can add more power, down shift the truck and it stops bucking. I'm thinking vac leak. Does this thing have a crank position sensor or something else that could be causing the timing to shift under certain conditions?
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Wednesday, November 11th, 2009 AT 8:32 PM

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