2006 f150 5.4 3.55 with 35s. Sometimes when I'm at a stop and accelerate right when I accelerate there is a single dull knock I'm pretty sure is coming from the engine, I run 91 with a custom tuned gryphon and cold air Intake. My main concern is I don't want to be doing harm to my engine, thanks

 

Any ideas of what it could be would be helpful

 

Try loading an 87 tune and see if that makes a difference.

 

There were some 5.4 engines of your vintage that could have a dull knock from a piston issue. This was/is not a durability concern..if its the same noise I am aware of. The old 5.0 pushrod v8 had the same type of noise in about 10-15% of them and it was never a durability concern for them either.
My son had a 2006 5.4 f150 with a single cyl dull tap at certain times which started a few months after he leased it new. He works at Ford so he had friends at Dearborn NVH check it out and they determined it was a non issue in terms of durability. His buddy bought the truck and is still driving it with well over 100,000 miles with no problems. Not saying your trucks noise is the same condition.
When you say a single dull knock do you mean you only hear it knock one time or it sounds like only one cyl knocking constant? It sounds like you only hear this noise during an acceleration from a stop. If this is true then could it possibly be a drive train component or an exhaust leak? My 97 has a dull thud sound when cold but it is from the exhaust system, actually the muffler.

 

I'm sure it is not exhaust I just had that checked and had it redone And I mean one single knock only once from take of from a stop, if I really feather the pedal it probably won't happen but normal acceleration from a stop I will usually hear it

 

Check your u-joints. I'm thinking it might be driveline related and you need to rule that out. It could also be the slip yoke splines.

 

Yes that's why I asked for clarification on the knock. A single knock would tend to be drivetrain, possibly the slip yoke as these trucks have that condition sometimes even when they are completely stock. Anyway understanding what the exact condition is makes a world of difference in solving the problem...lol

 

It could also be spark knock, which is why I suggested running a lower octane tune.

 

U joints seemed fine the only thing was the joint on the tranny side moved up and down a just a little bit but everything was solid

 

Are you sure it isn't the front suspension?

 

We are both at a huge disadvantage trying to decipher a written discription of a condition that lends its self to many variations of a "noise" and that is not the fault of anyone even the person writing it. Its just the nature of the beast when using the web, phone or written word for problem solving..lol.
As we used to say when talking with dealerships across the country. A knock in Texas is a tick in Florida, is tap in New York. You would be surprised how much geographic's can change the entire diagnostic thought process...true! So with that said.. who knows, is it a rattle, knock, tapping, tick? The only thing that we have for certain is that it is just "one" only on initial acceleration...not a continuous knock, rattle, such as spark knock, "preignition". But then again maybe I am misinterpreting the OP.....lol.. You see where I'm going with this GLC and I have the highest respect for you here on this site... Just a different spin on the realities of diagnosis that each of us deal with while trying to help someone here on the web. The main thing is that we are doing our best to help that person solve a problem...Take care my friend.

 

I have heard a single spark knock when tipping into the throttle in the past - that's the reason why I'm holding this out as a suggestion. This is more likely running a non-stock tune than if the truck were stock.

Somehow that just doesn't seem right.

 

I have never had much experience with anything but factory stock so you may be on to something. Universal joint..questionable I think as well, no mention of vibration but you never know. I do know the drive shaft slip joint can make some noise on startup from a stop because I struggled with that on my 97 and know others that had it as well and not just Ford but GM as well.

 

Just to try to clear things up, this is a dull knock, NOT a ping, this is a sound similar to knocking your Hand on wood not the same but that kind of dull tone only happens once and on the tranny side I can move the drive shaft up and down just a little bit is this normal?

 

Little bit of a thread jack. You mention the old 302s may experience a rod knock, well my 302 has recently been a victim of this. 40k km unto the re-maned long block. The noise becomes more prominent when oils warm. 100% now it's rod, every stroke, only the one.

Although it may not be a problem is there anything that can be done about it. Like a pull and clean of the lifter?