Truck: 2006 f-150 5.4 triton motor 123,000 miles 2 wheel drive

Hello. Im a first time user on this site so i hope i post this in the right place.

Heres my problem. The truck some times hesitates and has a small miss under load. very rarely at idle it will skip a beat or two. here is tht history:

Truck was purchased new by a friend of mine. He installed K&N intake and had the truck "Chipped" or "Tuned" (not sure which is right term) and he included the programmer "Flashpack". He also has adjustable coil overs and the front and air Fox shocks in the back with over-sized knobby tires. All this work was done the week he bought it new from the dealer. The truck spent most of its life in Tahachapi on dirt roads. he was a hard driver but kept up on the maintenance. I dont think he ever had any issues with the truck.

The truck had 84,000 miles when i got it. The flashpack setting was set to performance and recommended 91 octane. The truck was set to that its whole life. When i got it i changed transmission fluid, fuel filter, air filter, oil, etc. I also ran some sea foam thru it and everything ran great. At about 90,000 miles i attempted to change the spark plugs. One plug broke and i purchased Listle plug extractor ($125) made for these motors and i replaced all 8 plugs with motorcraft platinum $9.99 each from o'rielies. Truck was running great.

Amount the same time i noticed i had a small exhaust leak from the passenger side exhaust manifold. I bought gasketsa, and attemped to change the manifold gasket my self, but after job was done, i still had slight leak and it sounded the same. I took it to a shop and they replaced the manifold gasket again and the same small leak still there and mechanics say manifold is slightly warped. The sound goes away once truck is warm and i have left it like this since them.

About a year ago, I had to replace both upper control arms in front, and i lowered coil overs to lowest position. (almost stock height) The tires were wearing on the inside and i went thru a set in a year and upper ball joint was taking extra pressure from being lifted in the front. I replaced upper control arms, and tie rod ends and put new stock size tires on stock wheels and had everything aligned and all is ok. **Note: Also discovered spectrometer was off, at 60 mph it showed 70+. Found out the settings in computer were set wrong when he changed tire size and the miles may not be tru. There is probably less miles than what shows. I dont know how long it was like that. But at that time i wanted to save a bit of money so i hooked up the flashpack and set the truck back to factory settings instead of performance settings and it said recommended 87 gas. So i started putting regular gas. I noticed a little less power and less pep when i did the change and the motor seemed to shift sooner or something and didn't let rpm go as high as it did in proformance mode. but still drove great.

About 4 months ago at about 120,000 i started feeling like the power was getting slightly lower, or something. Almost as if the rpm were too slow and motor had slight miss (no code or MIL). I assumed that it was fuel related. I started by changing the fuel filter - No change, but problem was getting more often. I then got a OBDii tester that shows engine data and tested fuel pressure. I did this at idle, under load, and even during a "Miss". Mostly stays around 39psi, and at miss would drop to 38 psi and go back to 39. I was able to force the truck to mis and i gave code for cyl 4 random misfire. (Same side with exhaust leak) My first thought was still fuel, so i moved all injectors one cylinder down, reset code and drove again. Same problem - again forced truck to throw code same code cyl 4. My next thought was bad coil? So i swapped each coil one cylinder- reset code- tried again. Problem the same- forced to throw code - same code cyl 4.

I didnt think it could be plugs because they only had about 30,000 miles, but at about 123,000 miles (a week ago) i pulled plugs and replaced with motocraft premium platinum $19.99 each at. I noticed the plugs on the passenger side were dirtier that the drivers side but over all they looked good. This was a big improvement and at first i thought the problem was solved.

I changed plugs about a week ago and have only driven about 100 miles and the slight miss under load is coming back. If i turn on off over drive it seems to fix it, but i really want to finds the cause. Now its so subtle that i cannot make it mis enough to throw a code, but its defiantly there and sometimes will miss and buck at freeway speeds like its not getting fuel for one sec then its ok. like a hiccup, of a few hiccups.

Im at a loss. I can only think maybe fuel pressure, or could a bad cat do it?

Im going to try to change the flashpack settings back to performance and see if that cures the problem, but i tried that before i put new plugs and it seemed the same so i put it back to factory settings. Now with new plugs ill try it and see if there is a difference, but has anyone got any ideas on what it may be?

 

Did you change the coil on plugs while doing the plugs?

By the way you are posting in the 09-14 forums. Probably be best in the 04-08 forums

 

Posted-in 2009 - 2014 F-150 ...Recommendation .....

• ditch the "K&N" intake. *Or at least replace the oiled filter for a dry.
  .
• clean the MAF ...
  

.

 

thread moved to V8 section


If your coil boots have brown hot spots then you need to replace the boots at a minimum

 

I have changed the settings with the Flashpack back to performance. I went on a 100 mile round trip drive and i can feel the performance setting change but still have a random miss-fire or hiccup. Still seems to happen mostly under load. For example, ill be driving along on the freeway at 65-70mph and the freeway starts to go uphill. No change in pressure on gas pedal and truck starts to miss a little. I have to give it a little more gas, or make it downshift and its fine. I also notice if i turn overdrive off it seems to be better, but i feel like this only masks the problem.

i really dont know what to do next.

 

Have the boots between the COPs and plugs ever been changed? Other things, clean the MAF and throttle body. Have the catalytic converters checked.

 

The boots were changed around 90,000. I think im going to pick up a can of MAF sensor cleaner and clean throttle body, replace all coil boots, and see how it goes. Ill post an update soon. Thanks guys

 

Pick up a can of throttle body cleaner too, and remove it from the intake to clean it. I've been told not to move the throttle plate by hand if the actuator is still connected.

 

replacing it might fix ur issue also this happen to me in a 4.6 ford engine and the cause was I used diesel oil, so i was told messed up the compression, do a compression check in cilinder 4, maybe ur loosing compression on it , it's not a bad coil, when a coil is messed up ur engine really shakes while idling also check Ani little vacuum leaks ,

 

i have cleaned the MAF sensor and the throttle body. Truck does seem slightly better but still has the random mis. I was able to get it to throw a code and the code has moved to cyl 3. Im beginning to suspect the injectors are dirty, or at lease #3. Does it make senses to change only one injector or should all 8 be changed at once. Has anyone ever purchased one of the injector rebuild kits? is it possible or even worth it to try? The injectors are expensive to try and not really know if its them or not.

Im going to check the EGR valve tonight. I Have checked and listened for vacuum leaks and it doesn't seem to be vacuum. Although a vacuum leak has had me stampeded on other cars before... I will check again for any vacuum leaks.

I feel like the compression is good, but i should check compression as well. Ill see if i can borrow a test kit from a buddy. Ill update once i get these tings done and tested.

 

I don't think it's the injectors since ur misfire moved from cilinder 4 to cilinder 3 , fuel injectors do get clogged up but ur truck ain't that old so.i don't think it has to do with fuel injectors ,, I have a 2002 still running on original injectors , the only way they would fail it's if they are phisicaly broken , wich they would be leaking gas ,