My boss' truck has a bit of a stumble. While going down the road between 40-60 MPH it will kind of stumble. While it's an intermittant problem, it seems to happen when climbing a slight grade.
I plugged a diagnostic tool into it and got no codes of any kind. He had it at a trans shop, thinking there might be some trans slippage, but the shop said the trans was fine.
The vehicle in question is a 2006 F-150 Lariot 2WD with a 5.4, auto trans. Any ideas?
Hartski

 

Coil going bad maybe?

 

Check plugs too. My truck had a stumble around 1250-1500 RPM, turns out all coils are good, but the plugs were going bad. All replaced, runs perfect now.

 

Thanks for the tips guys, I'll be sure to pass them along. BTW, the truck has 160,000 miles.
Hartski

 

Have the plugs been changed since new? If not I would bet it's a bad plug, second guess is a bad coil. A bad coil may not throw a code. If money is not a major concern you can get 8 new non-oem coils for around $120. Wouldn't hurt to swap them all at that mileage. Takes about an hour. How does it idle?

 

It idles OK, I know some of the coils have been changed but I don't know which ones.
I was on the Autolite website getting some info on the spark plugs and they have a very elaborate procedure for changing them. it involves loosening the plugs, soaking everything with carb cleaner, and waiting 1/2 an hours for the carbon to loosen.
Is all that really necessary?
Who sells those coils?
Hartski

 

Yeah, the 04 to 06 5.4l 3v had a bad plug design that caused them to break off. Even with careful soaking and caution there is a chance you will break one and then need special tools to remove broken plug. There are a ton of threads on this.

How many miles on the truck?

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160K. Some of the plugs have been changed but not all. At this point I don't know which have been changed and which haven't.
he wants me to do this on the side for him but I'm starting to think that I want no part of it.
Thanks for the heads up.
Hartski

 

Yeah, not sure why only some of the plugs have been changed-with that many miles plugs are long overdue. Find a competent mechanic who has exp with fords and the spark plug issue-it's somewhat common. The broken plugs can be removed with the right tool-not impossible, just a pain. After all plugs are changed, change fuel filter. If that doesn't cure it, coils.

 

The dealer did mine, cost about $600 for everything, no plugs broke. With that many miles those plugs should have been changed on your bosses' truck, at least once. Ford recommends every 60K now for change