I have a F-150 xlt with a triton v-8 5.4l and the truck skips or bucks while driving. I have replaced spark plugs coils fixed vaccum line and changed fuel and airfilter could you please let me know what else I need to be checking to figure out this problem. Thank you

 

Which replacement parts were used?

 

we used motocraft coils and spark plugs but used wix fuel and airfilter

 

Try cleaning the MAF sensor.

No check engine light? How many miles on her?

 

Yea, I have the same question, - is there a CEL illuminated ?

 

You used good replacement parts, but, coils are prone to being bad right out of the box. Sounds like you have a bad new one, - it's common. Hopefully you get a CEL directing you to cylinder with the bad coil. Also, you could have more than just one bad one. I purchased a new set of Motorcrafts on ebay and had two fail within 6 months. That's what you have to contend with as far as coils, - it doesn't matter where you purchase them from it seems.

If you get a CEL, try swapping the coil with one of the coils from your previous set first.

 

Shortly after I swapped my 5.4 in I had a similar issue. Turns out it was a manufacturer defect in one of the new plugs I had installed causing the bucking. First it would be nice if you can get a CEL as to which cylinder is giving you grief.

Did this issue arise after the new parts or did you install these parts in an attempt to fix the "bucking" (misfiring). Could be many issues that are causing this. Could also be a bad injector but I'm a little hesitant to point to that as the source. Also have you given the motor a thorough check to make sure you have no air leaks after the MAF? Especially the rubber elbow at the rear of the throttle body? could be something as simple as too lean. However before I fill an entire page with guesses as to what it could be, try to get a CEL if you can. And surely somebody will know what the best plan of attack is.

 

Hello to all that helped me in this endevore.
1. CEL is on says cylnder 4 misfire. Primary wire on ing coil.
I changed again, also took meter and checked ohms. Changed plug again.
Went down the road, ran fine for about 1mile, Took next left and went up hill. As soon as it was under a load (going uphill) I gave it some gas, she turned right to bucking. Went home and it was misfireing and bucking on flat road as well like no fuel.
I replaced the injector today, still not doing good. The Spark plug looks like blueing,has a shade of bule on the top, no carbin, Almost looks like its just fireing but no fuel.
Im stepping outside fo about hour, going to run compression test on cyclnder, let ya know the results.
Thank you for your responces been very helpful, any more ideas would be great.
Truck has 170k. Had the truck since it was brand new. We have done all work on truck. It has ran nice till this happened.
Well wait to hear some more ideas.

 

sounds like you might be loosing a pump. do a fuel pressure test. and a fuel vol. check just because you have pressure it doesnt mean you have vol.

Hey look college is paying off!!

 

Well... what are the odds that the injector you swapped in wasn't working properly? I suppose we'll know the results of the comp test soon enough to be able to determine if that's a cause or not. If the comp checks O.K. You might check the intake manifold gasket. They don't go out often on these trucks but I have seen it in the past. Just spray a small amount of starting fluid around the intake and head where cyl 4 is and see if there is any noticeable change.

If the compression doesn't check do you have the ability to pull a valve cover and inspect the valves/cam at that cylinder? Seems like cyl 4 is prone to having valves getting stuck. Seems to me I've heard mention that the jacket between the exhaust port and the valve is thin and it gets too hot. Fix might be driving the truck hard. ?