Not to long ago I traded my truck in on a 08 F250 with 103K on it. I am fairly new to the diesel market but I am aware of what it takes to maintain these engines. My question is, when accelerating mildly, I here a chatter or something similar like you would hear on maybe an older diesel. It will do it until I settle in to a speed and let off. If I give it more throttle it will get a little louder but if I let it downshift and hit it hard It is not as noticeable. Is this normal noise or rocker arm issues or part of the TSB for the chatter? I have searched and cant find a video of the rocker arm noise or the noise that the TSB is suppose to be. Truck is deleted with a mild tune and I think 5" exhaust.

 

I should also say that I do not hear it at idle.

 

Bump........

 

Sorry I missed this yesterday.

I am 90% sure what you are hearing is pilot injection shutting off. Our injectors are capable of 5 injection events per firing cycle. This means that the pcm can control how and when combustion occurs. It also smooths the sound of the engine down A LOT. Stock tuning will start reducing pilot injection right around 1700rpm. A lot of tow tunes will keep pilot injection on to limit cylinder pressure till well above 2k rpm.


Pilot injection itself just ensures complete combustion and lower emissions. But at certain points in the power band the pcm will command it off to allow for more power (more fuel=more power). Its quite complicated, but long story short its normal.


If you can get video of it and post it up on here so we can listen to it. There is always the chance its something else, but almost anyone who owns a 6.4 has questioned this noise in the past. And it is present on any modern common rail diesel. It was first used in Ford's when the split from OBS to Super Duty happened with the 7.3 and it went from single shot injectors to dual shot. The idea is to control the combustion event more carefully.


Probably more explanation than you needed and I would still like a video just to make sure.

 

I appreciate the feedback! I will do what I can to get a video up but it is mostly present during driving while taking off. I know some videos don't have good sound quality but I will give it a shot.

 

Yah it sounds to me like pilot injection.

 

Is this something that could be overcome with a specific tune?

 

Here is the deal with our trucks. (Yes this is going to get technical and boring, sorry...)

The injection system in a 6.4 is capable of 5 separate firing cycles within a single combustion event. This is what a multi shot injector is. It is also how pilot injection works. The injector will fire a small amount of fuel pre combustion just to kick things off. The idea is to spread the combustion cycle out and get a complete burn. This also limits cylinder pressure spikes (that cause damage to pistons) and noise. The pcm will slowly condense the firing cycles of the injector as rpm rises (because as boost and rpm rise you are able to shed heat and there is enough exhaust gas being expelled for the extra cylinder pressure to not harm the motor) until they become "single" shots of fuel (you never really get only 1 shot of fuel but its easier to explain it this way) for max power when boost can support it.




NOOoowowowowowowowoowowo (I am trying to condense this as much as possible, there is A LOT more to it. If you really wan't an education call Matt at Gearhead Auto or Vivian at QuickTricks. Or your local diesel shop.... Or google.... Or the library... Anyway)

This quote is from Toren on Powerstroke.org and is a very basic explanation on how fuel timing works in a 6.4 (again this is a VERY small snip-it)
"Remeber the type of injectors the 6.4 has and their ability. In the 6.0 timing and pulse width will go hand and hand, but with the 6.4 and the Peizo sticks it has, timing can be "set" if you will and then PW can be manipulated to active the power level desired. Also factor in the pilot injection aspect and it gets more acurate while leaving timing at a nominal setting."

What all this means is that pilot injection is manipulated based on desired power level. It is also why many tunes (until you get into the 200+hp range) feel the same down low in the power band. They keep pilot injection going to keep smoke output down, egts in check, proper turbo spool, and cylinder pressures (especially when cold) stable. Once you stand on the go pedal you will hear exactly what you described as an "old school diesel sound".


Depending on tuning the pcm will utilize pilot injection in different ways. In tow tunes the pcm will command multiple injection cycles (pilot injection) up past 2k rpm (I have one that you won't get the single shot chatter until 2500rpm). They also limit fuel to control egts and the vgt system in the turbo will stay closed longer to keep boost up above 10psi (on the freeway you will usually see upwards of 15-20 when cruising).

Now a race tune for example may cut pilot injection somewhere around 1500rpm. You will also see much higher rail pressure to provide for all that extra fuel. Its also going to adjust the injection timing to increase cylinder pressure.

Stock will start cutting pilot injection somewhere around 1700rpm.


A lot of that noise also has to do with how much fuel is being pushed. But, the clatter you hear that seems to start abruptly at around 1700rpm is completely normal. it is just the pcm shutting off pilot injection.


Sorry for the wall of text lol, hope it helps. Long story short is that pilot injection is nothing to worry about, I recommend learning when it starts chattering and trying to keep rpm below that point until you get some heat in the motor. It does increase cylinder pressure, but a stock or tow tune it isn't going to hurt anything at all as long as you don't have your foot to the floor when its cold.