drunk on diesel
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yeah, no... I'd get back in a Dodge before I got into one of those piles. And that's saying a LOT because I think Dodges are piles!
2015-2016 Super Duty Active Regeneration Jack Hammer Valve Issue
- Thread starter nchighcountry
- Start date
To explain what happens a bit more....
The issue occurs only during regen, and only at very low RPM.
A slight change in RPM, or a slight change in engine load and the problem is not there.
If it were in fact improper valve guide clearance, this issue would be more prominent other than these very specific scenarios. It would be duplicated at somewhat varying RPM's, and at many different engine loads. It would also present itself outside of a regen cycle. Furthermore, if they were sticking that bad and making contact with the pistons, there would be marks, damage, etc. But that's not happening.
Tolerances are easy to measure. Ford has not found this to be the issue or the cause. They have done repairs simply to try and appease customers because they had a hard time locating the specific issue. It's hard to duplicate and you have to be in the right place at the right time for it to happen. If you have customers screaming and you don't know how to fix it, throw parts at it and hope for the best, keep testing until you find the solution.
So let's dive further into what happens, because there are a few interesting quirks that many folks here might not be aware of....
Ok, so we've established that when you vary engine load and RPM, the problem disappears.
Also interesting to note is that this only occurs early in the regen cycle, and not happening later in the regen. I've tried over and over again on my truck, I can't duplicate it more than halfway through a regen. Same is being reported across various forums and by many owners. This is also why dealers have difficulty duplicating when they do a forced regen, especially when the exhaust filter is well under being full.
The problem is far more prominent in the 15 and up model year. There were significant changes.
It has been discovered by a few tuners that they can simply make a few tweaks to the calibration, and the problem disappears.
So when you look at that, what other significant factor could cause the issue? The theory I heard is.... pressure. Pressure changes with RPM and engine load. Pressure changes as you get further into the regen cycle, even at the same load and RPM that cause the problem earlier in the cycle. Pressure is different on the 15+ model years, making the issue easier to duplicate and far more prominent. Tweak the calibration a bit, and you change pressure and the problem goes away.
With that said, how do you guys think pressure plays a role here?
lincolnlocker
Well-known member
as i stated, it just reminded me of the back pressure holding valves open on the 7.3s..
i dont have the problem, im just trying to understand whats going on.. it may be valvetrain slap and not hitting the piston.. if its a tuning tweak, what is being tweaked to remidy the issue?
live life full throttle
i dont have the problem, im just trying to understand whats going on.. it may be valvetrain slap and not hitting the piston.. if its a tuning tweak, what is being tweaked to remidy the issue?
live life full throttle
I used the EBPV a ton when I towed with the dually. Never knew there was an issue with that?
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lincolnlocker
Well-known member
i did too.. if you drove like i do, 8 bent pushrods later down the road, it messes them up.. my first rebuild showed valve marks on all pistons.
live life full throttle
Forgot the brake on and gave it throttle? Lol
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lincolnlocker
Well-known member
no.. i have the old powerstroke power braker.. flip a switch to activate it and when you lift off the throttle and applied brake pressure, it automatically closed the ebpv.. as soon as you touched the skinny, it opened back up.. i ment how i drive on a daily basis with my dually.. pretty much wot everywhere i went even when towing.. no matter the load...
live life full throttle
Maryland dieselnick
Member
Tuning tweeks that change the thermal dynamics can stop the thermal expansion causing the stiction. It all depends on how tight the guide to stem clearance is in the guides that are in that head.
drunk on diesel
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Can you explain why replacing the head or valves makes the problems go away?
They don't go away.
I know one dealer that has done 3 and all of them had the problem return.
Maryland dieselnick
Member
Sure, the trucks that have this happen have guides that have inside diameters that came thru smaller than they should be. When the valve stem is inside of it, there is not enough room between the stem and guide to accommodate the normal film that builds up on stem due to exhaust gasses escape venting up that guide any and all times the exhaust gas back pressure exceeds atmosphere pressure, which is normal for all engines, AND still have adequate clearance to additionally accommodate the expansion that occurs due to a $7 and change valve and this guide gets blasted while the valve is open during the exhaust stroke with extreme heat from the injector firing on that stroke.
This valve has a spring trying to pull it closed while open.
When the thermal expansion reaches its max, it causes what known as thermal expansion stiction.
Thermal expansion is not a "seizure" in the classical sense.
It is "stuck"
While in this static state due to this stiction, the spring still has stored energy within itself trying to pull that valve closed.
It is on the razor line of remaining in this static state and having the spring pull it closed.
Because it's on that razor line, it offers little resistance to the piston pushing it out of that static state.
Due to the valve offering little resistance to this combined with the valve geometry used, a straight up motion, the piston puts virtually no lateral force on this valve, which would be a catastrophic event immediately, this is not the case with the 6.7 and is why besides the violent bucking and no power, it tolerates this for a while.
The new head has new guides that hopefully are ok
****** if the tech does not verify the new heads guides are not too tight on the new head, the truck will be right back******
This valve has a spring trying to pull it closed while open.
When the thermal expansion reaches its max, it causes what known as thermal expansion stiction.
Thermal expansion is not a "seizure" in the classical sense.
It is "stuck"
While in this static state due to this stiction, the spring still has stored energy within itself trying to pull that valve closed.
It is on the razor line of remaining in this static state and having the spring pull it closed.
Because it's on that razor line, it offers little resistance to the piston pushing it out of that static state.
Due to the valve offering little resistance to this combined with the valve geometry used, a straight up motion, the piston puts virtually no lateral force on this valve, which would be a catastrophic event immediately, this is not the case with the 6.7 and is why besides the violent bucking and no power, it tolerates this for a while.
The new head has new guides that hopefully are ok
****** if the tech does not verify the new heads guides are not too tight on the new head, the truck will be right back******
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There would still be marks on the pistons and valves.
And you still can't explain why this only happens earlier in the regen cycle, and also why it only happens at very specific RPM's and engine loads.
Thermal expansion on the valve stems causing sticking valves would have the symptoms persist as you continue to apply heat. Thermal expansion wouldn't care about RPM's, only heat. In fact, if the valves were sticking, increasing RPM's would make the problem WORSE, causing even more problems. And because this heat is continuously applied, it would also keep occurring late into the regen as well. Yet it all magically disappears when you downshift and increase RPM's, and also as the regen continues along.
Maryland dieselnick
Member
Yes down shift, giving it fuel, or letting off changes the thermal dynamic thru air flow, fuel flow via different injection duration and injection event counts. Lots of variables and things change the thermal dynamics which only are holding that valve back from closing due to the stored energy in the spring. (Little resistance)It depends on the exact truck and how much resistance is offered. This is why a few cannot manipulate the event and get out of it at all if the resistance is more substantial.
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Maryland dieselnick
Member
Ford is not paying the tech to pull the springs on the new head to verify adequate clearances so if the tech does not take it upon himself to check and that head come thru with the same situation the truck is coming back.
They do not all come back, note that the truck featured here has been out for over 10k now with no further problem. I know of another that has gone so far 50k without further issue.
They do not all come back, note that the truck featured here has been out for over 10k now with no further problem. I know of another that has gone so far 50k without further issue.
Basically you're saying that thermal expansion on the valve stem itself is instantaneous and doesn't actually follow temperatures.
Maryland dieselnick
Member
I'm not sure instantaneous is the word I personally would use. It does follow temp.
The key to getting ones head around the event is to keep in mind, thermal expansion is going on. Now it has a point where the clearance in the stem is taken up by this expansion.
It does not "seize" in place but rather it hits a threshold point where it creates enough resistance to overcome the stored energy in the spring trying to pull it back. This margin can be extremely thin so virtually any change in the dynamics in the combustion chamber, ie, back pressure, air charge and or fueling ect will tip the scales in the opposite direction.
But Curtis yes I think this is where your question originate from, that it is a very fast occurring situation that is a physical condition on a razors edge of not even happening at all, Hanse the very often almost just enough to cross the line of offering enough resistance while in its static state to overcome the stored energy in the spring trying to pull it closed.
The key to getting ones head around the event is to keep in mind, thermal expansion is going on. Now it has a point where the clearance in the stem is taken up by this expansion.
It does not "seize" in place but rather it hits a threshold point where it creates enough resistance to overcome the stored energy in the spring trying to pull it back. This margin can be extremely thin so virtually any change in the dynamics in the combustion chamber, ie, back pressure, air charge and or fueling ect will tip the scales in the opposite direction.
But Curtis yes I think this is where your question originate from, that it is a very fast occurring situation that is a physical condition on a razors edge of not even happening at all, Hanse the very often almost just enough to cross the line of offering enough resistance while in its static state to overcome the stored energy in the spring trying to pull it closed.
Maryland dieselnick
Member
I'm not sure instantaneous is the word I personally would use. It does follow temp.
The key to getting ones head around the event is to keep in mind, thermal expansion is going on. Now it has a point where the stem guide clearance is taken up by this expansion.
It does not "seize" in place but rather it hits a threshold point where it creates enough resistance to overcome the stored energy in the spring trying to pull it back. This margin can be extremely thin so virtually any change in the dynamics in the combustion chamber, ie, back pressure, air charge and or fueling ect will tip the scales in the opposite direction.
But Curtis yes I think this is where your question originates from, that it is a very fast occurring situation that is a physical condition on a razors edge of not even happening at all, hence that very often almost just enough to cross the line of offering enough resistance while in its static state to overcome the stored energy in the spring trying to pull it closed.
The key to getting ones head around the event is to keep in mind, thermal expansion is going on. Now it has a point where the stem guide clearance is taken up by this expansion.
It does not "seize" in place but rather it hits a threshold point where it creates enough resistance to overcome the stored energy in the spring trying to pull it back. This margin can be extremely thin so virtually any change in the dynamics in the combustion chamber, ie, back pressure, air charge and or fueling ect will tip the scales in the opposite direction.
But Curtis yes I think this is where your question originates from, that it is a very fast occurring situation that is a physical condition on a razors edge of not even happening at all, hence that very often almost just enough to cross the line of offering enough resistance while in its static state to overcome the stored energy in the spring trying to pull it closed.
Shinny
New member
Mine started at 4000 miles, usually starts in 6th gear at 50mph. I go to accelerate(the gradual acceleration to where it doesn't downshift) then it will start bucking. If I manually downshift to 5th, it goes away unless the rpm lowers to the point at which the 6th gear and 50 mph started, then it happens again. Repeat to 4th gear...works the same way
ONLY during REGEN! when I haul my camper, REGEN never happens
Runs like a pcp junkie any other time...
thanks everyone for posting to this thread...I have found it very informative...I'm just going to do the *** ******!
ONLY during REGEN! when I haul my camper, REGEN never happens
Runs like a pcp junkie any other time...
thanks everyone for posting to this thread...I have found it very informative...I'm just going to do the *** ******!
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Shinny
New member
hahahaha the astericks are funny
