Our '16 will make 25psi going up Mt ord/payson at 55mph with the toy hauler @~10k.

 

A great read/thread. 37's, camper, boat, I'd throw in some 4.30's, dealership can program the ratio in no problem, it will pull like mad and still work great empty

 

Been running 37s for over a year now and they don't seem to have negatively affected hill climb performance or mileage compared to 35s.
Made the same lake tip, 100* at the Ord summit, 52mph indicated (56gps) in 4th gear.
37 don't even look big. Quite a few other rigs running 37s on the beach, guess its a normal size now.

 

I'm experiencing this exact same problem, but on stock tires. Same 3.55 gearing, 2012 f350.

I've taken to data logging as well, but with forscan for the moment (because livelink for my livewire does not have the PID's I need, I'm working to fix that and get a release out that will add them so everyone has them).

I see very similar numbers as to what you're seeing. What I've noticed in particular is that no matter what I do the fuel rate in 1st and 2nd gear is great, but 3rd gear and above it drops to below 1 liter/hour. It does not matter what tune I run, street, tow, or performance. The tunes slightly change the fuel rate in 1st and 2nd gear, and mostly they seem to change injector timing (further before top dead center). The results are the same each time though, I end up with the pedal to the floor and can only hold 60-65 with an 8000 lbs load up big hills. Vail pass I hold 55-60.

My friends 2006 duramax LBZ pulls up those same hills at 80 with no problem, with the exact same trailer and load.

I don't think boost is the issue because the engine is flowing the same MAF lbs/s at all gears, but the fuel rate is always goes down 3rd gear and up. I'm working with gear head tuning right now to see if we can figure out what is going on. I don't think EGT is the issue either because I see it do the same thing using the on ramp to get onto the high way even if EGT11 is reading under 600 degrees when I hit 3rd gear. I even forced a 3rd gear only pull in manual mode and found the same issue with fuel rate. Part of me wonders if it's a transmission issue and it's requesting a limit in 3rd gear, or maybe just a tuning issue (the tunes above are not from gear head, they are the OTS tunes from the livewire).

If I have to I'll put a meth kit on it, but for the moment I really want to know why it pulls so much fuel in 3rd gear and above. Doesn't matter if the trailer is attached or not, tow mode or not, the numbers are the same.

 

Something is not right with your tunes. I can hold vail at 60-65 with a 16K load. Gets slower as you get closer to the tunnels.

 

I may have just figured it out... after hours and hours data logging, after getting IDS working and cross referencing it's PID's vs forscan (they are nearly identical but forscan is much easier to use and I can save the logs as *.csv, which then lets me use data zap) and cross referencing the FORD pdf of the truck... I think I found my smoking gun:

If you actually read this monster: http://dpefuel.com/wp-content/upload...sel-Engine.pdf

You'll see a comment on the NOX sensor where it says the NOX sensor can affect fuel trim... well, look at these two logs:
https://datazap.me/u/shushikiary/67-...3&mark=615-895
and this one: https://datazap.me/u/shushikiary/67-...3&mark=539-820

You can see, exactly when NOX hits 900ppm, she defuels.

Damn emissions crap. But at least now I have a smoking gun to go after with tuning.

This would imply that I'm not flowing enough DEF (but not low enough to throw a code) or the SCR is not working right. I just replaced both the DEF dump and injector... I'm going to bet it's a bad SCR.

 

Thats a really cool find and great use of Data logging to find this. Forscan is a godsend, especially for those of us who don't have access to IDS.

I'll be curious to hear what you find out as the root cause for the High NOx issue.

 

She passes the IDS dousing test for the DEF flow. That's why it's likely not throwing any codes there. There are also no codes for a bad NOX sensor or module. There are learned adaptations for the NOX sensor though, and you usually have to reset them when you replace the sensor, someone might have reset them before I got the truck, or the issue is not bad enough for it to throw a code.

I'd bet there's a very high likelihood the SCR catalyst is not working right. I had to replace the turbo on it about 4k miles ago, and I bet enough oil went down the exhaust to muck with the SCR catalyst (combined with the mileage of the truck (220k), it's very likely the catalyst is toast.

That would mean a 2300 dollar part for a whole new "torpedo" (DOC/DPF/SCR, all one unit). That or a delete is coming down the pipes unless I can get a tune that removes the de-fuel based on NOX.

Talking with some tuners, it seems it's also possible that low EGR flow could cause high NOX, and the log shows it's requesting max EGR. Though one would think that it would blow a DTC if that was bad enough.

I'm working all those avenues at the moment, we'll see what happens and I'll post back.

 

I have results, there were two limits involved.

My SCR catalyst is indeed bad, we can practically prove it. Delete tune solve the issue on short pulls. Towing up a hill the EGT's would get too hot and she would still de-fuel (once you hit 950 or above for EGT11 it starts to defuel and gets more aggressive as the temp goes up, this is because pre-turbo pyro numbers show the EGT's in the 1300's when EGT11 is at 950 or so, so they must be back calculating pre-turbo EGT from EGT11). EGT's were so high because it was a delete tune but with the torpedo still in place.

Next step is to race pipe it, and watch her fly.

Edit:
Results with weight reduction: HOLY COW she's a monster. Even on just a tow tune she'll easily pull more than 80 up any hill, you just have to watch your EGT's and make sure they don't get too hot for too long.

 

I can run EGT 11 full throttle, with no derate at 1100F. So I would be ok with that temp.

 

I wonder if different strategy versions of the PCM code have different limits, or perhaps different years of the truck. Or maybe it's a combination of temp and back pressure or something. Aka, if your DPF back pressure is X and your EGT11 is Y then de-rate.

 

I'm curious about this derate on high EGT's as well (or lack of).

Seems that the truck derating on High EGT11 Readings would be a good thing to prevent engine melt down. I've posted elsewhere on this forum about my previous 6.0 that got VERRRRY Hot when the cold side CAC tube blew apart pulling my 5th wheel. Pre Turbo EGTs hit 1500 F before I even realized it, and that was with me just trying to limp to the next town at 30 MPH. EGTs get very high when the truck is making zero boost and continuing to fuel.

If the 6.7 is smart enough to de fuel when EGT 11 starts to climb too high, (such as if the cold side intercooler tube blows leaving the truck with no boost), then it would prevent total engine meltdown. If it does not defuel, then all the more reason to still and not keep driving on a blown CAC tube, even to get to the next town like I foolishly did with my 6.0.

This makes me curious though. I'm *almost* tempted to unhook my cold air charge tube and go for a drive while watching fuel rate and EGT11. ALMOST tempted. Anyone else wanna do it?

 

From looking at the tables in advantage, for sure the tables take MAP into account, and thus if your CAC tube came off, the MAP pressure would not be as high, thus less fuel. Now if that would de-rate even further because of EGT 11, not sure.

I know my DPF back pressure was consistently 4 psi under load, and my EGT 11 would not go above 950 because of the de-fuel.

Now on my deleted tow tunes I'm easily hitting 2.7 l/h fuel rates and hauling up the hills, I could hit 100mph up I-70 on the Dillon side. The key is to watch the EGT's because I can easily hit 1650 EGT when flooring it up the hill. If I just maintain 70mph or something it often will fluctuate between 1250 and 1350. (These are from the pre-turbo pyro). I asked the tuner if that was ok, he said on the 6.7's it's ok to be in the 1400's for a few minutes, and you can get up to 1800 as long as it's short bursts (under a minute), and anything under 1400 is ok for much longer. He's been running this same tune I am for over 6 years now with no issues. He also added an exhaust brake for me, which was really nice going down the hills.