2006 F150 XLT - 5.4 L, 4WD, 136K miles

The truck starts strong and idles smooth. After driving ~15 minutes the truck will start to knock and sounds like it's missing on some cylinders. When braking, the truck idles down and the knock corresponds to the engine RPM. As I come to a complete stop, the engine sounds as if it is just about to stall out but then the knock disappears and it idles smoothly. Occasionally the knock will maintain during idle, but then I feather-rev the motor and the knock disappears. OR I can turn off the engine during the idle-knocking and when I fire it back up the knock is gone. Until I drive again and the knock comes back immediately. Only when the engine is cold will the truck run smoothly for ~15 minute before the knocking begins.

If this is caused by cam phasers, wouldn't the knocking be most prevalent during idle?

There are 11 CE codes which I've attached to this post. I know that O2 sensors need replacement, but I don't want to leave out any details in case they are all related. I'm hesitant to start changing all these sensors that have an error in case there is a bigger problem causing all of this and the sensors are fine. Can anyone help me with this? I don't want to spend any money on parts that won't repair the root issue. Thank you.

 

Have the plugs been changed ?

 

I bought the truck 5 weeks ago and I have not changed the spark plugs. Could faulty plugs alone cause this issue?

 

yep !

 

I will get new plugs in immediately and see if this fixes the issue!

Thank you!

 

300/305/306 are all mis-fires that will effect other things.. change boots and springs while your at it..

 

Just for giggles, change the oil to a heavier weight. I would suggest castrol 0w40.

While the P0300, P0305, P0306 are definitely misfires and you would do well to change the plugs (not a minor undertaking if they break...get the lisle tool on hand for this), the P0340 level codes indicate your phasers are not synced properly to the cams. Cam phasers have a locking pin that engages at idle (with enough oil pressure) to lock the cams to the phasers, which is why, at idle, your problems often disappear.

Low oil pressure at the phaser causes this issue(when hot, this is why it doesn't happen when you first start it up) and when you tap the gas pedal the oil pressure increases. People will tell you there are small oil passages and "tight tolerances" but in reality, the 3V 5.4 was spec'd for a 30 or 40 weight oil (user's choice) when then were first released in the Ford Falcon in Australia in 2001, 3 years before hitting north american shores with EPA fuel economy standards. Honestly, you have very little to lose and I would bet your issues disappear. my 09 ran many years on 0w40 oil, towing and very cold winters as well. Plenty of fleets run a 40 weight oil in all their trucks without issue.

 

I will definitely try this! Thank you for the insight and thorough explanation.

 

Do you recommend changing the ignition coils altogether? Or just the boots and springs? I apologize for my confusion, but looking at them online it seems you can purchase only the boots and springs for about the same price you can buy all new coils... Is this correct?

 

Either way you're fine. Me personally, I bought EBay coils...50 bucks. 2 1/2 years later....works fine. Or...you can replace the boot and spring.