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Discussion starter · #21 ·
Got back from my trip today, the truck actually performed very well, most of my concern was unwarranted. I covered about 360 miles round trip into the mountains and back. This is the east coast, so it was really only about 2000 ft elevation change total, half of which was in the last 5 miles up a winding dirt road. I ran 60-65mph on the highway with no trouble.
EGTs stayed under 900 for the most part, other than a few grades where it would get in the 900s for a few seconds. Saw 1000 a couple times for just an instant. The higher EGTs happened on the highway in OD before it kicked down. On the 2 lane roads I was in "3" much of the time, and at higher rpms I could climb any of the hills hitting 10psi boost and never get past about 850 on the EGT. Coolant gauge never budged off 195 even on the slow grind at the end. I averaged around 10mpg which I thought was pretty good for a 4x4 with 4.10 gears. I only get 12-13 without pulling the trailer.

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Discussion starter · #22 ·
@TheJoggernot any "hard data" on EGTs and experience you've had with the hx35? How much boost are you typically producing? I was around 6psi normal cruising, and I saw 10-12 on hills. Even though I backed off the manual controller's screw a bit, I noticed it would still easily go past 15 if I just stomped it (just as a test). I don't have any desire to run more boost, but anything I can do to make it more efficient and reliable is worth it in my book.

One of my takeaways from my trip was that I need to rehab the brakes, so that is my first order of business. Then probably new injectors as they have never been replaced to my knowledge (close to 200k miles on it). Then I may start planning a turbo upgrade.
 
Discussion starter · #23 ·
So I have been experimenting with the boost controller, I currently have it dialed back so that it peaks barely over 10psi under heavy throttle.
Curious anomoly, I filled up with fuel and we put about 120 miles on the truck over the last couple of weeks. Yesterday I filled it up again before I head on a 700+mile trip (with diesel prices, ouch!). It would only hold 6 gallons. Unless my math is wrong, that is 20mpg! I thought maybe I wasn't getting it full so I kept topping it off, and it is definitely full. I still find it hard to believe that I would go from 12-13mpg unloaded to 20 just by reducing the boost a little.
I'm going to leave it set as it is for this long highway drive and I'll see how it goes and report back... If I could actually achieve 20mpg with this thing that would be amazing given the current diesel price landscape.
 
So I have been experimenting with the boost controller, I currently have it dialed back so that it peaks barely over 10psi under heavy throttle.
Curious anomoly, I filled up with fuel and we put about 120 miles on the truck over the last couple of weeks. Yesterday I filled it up again before I head on a 700+mile trip (with diesel prices, ouch!). It would only hold 6 gallons. Unless my math is wrong, that is 20mpg! I thought maybe I wasn't getting it full so I kept topping it off, and it is definitely full. I still find it hard to believe that I would go from 12-13mpg unloaded to 20 just by reducing the boost a little.
I'm going to leave it set as it is for this long highway drive and I'll see how it goes and report back... If I could actually achieve 20mpg with this thing that would be amazing given the current diesel price landscape.
Looking forward to your next report! (y)
 
I get 21 MPG in my truck @ 70 MPH freeway. Even better MPG if I slow down. Boost at that speed is around 3-4PSI. with Computer control.
Looks to me you are getting it dialed in right.
 
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That is a significant improvement. Just a guess here, could be lower boost with lower IAT makes the engine more efficient. Without a compressor map or IAT & MAF data, just a guess.

Higher boost that is also hotter does little to reduce peak EGT yet taxes the engine as it provides more back work on the engine. Net torque output is the pressure difference created by heating the charge by burning diesel.
 
Discussion starter · #27 ·
My results from my road trip were, well, inconclusive. I can't figure out where the error is. On Friday I filled up as full as I could get it, and hit the road. Stopped about 180 miles in and filled it back up again. I took 15 gallons and change, and I calculated 12 mpg, same as I have always seemingly been getting with the truck :(.
On the way back, hauling well over 1000lbs of firewood in the back from my Dad, I kind of messed up the calculations because I didn't get the trip meter reset properly and had about 30-40 miles 'unaccounted for'. But, I topped it off early into the return trip and logged @225 miles or more until I got home. The fuel gauge is sitting a mark above 1/2 tank, roughly the same place it was when I filled up at 180 miles on the trip out there. That is of course completely anecdotal data since I haven't filled up again yet, but it would appear to have gotten significantly better fuel mileage coming back even with an 8' bed full of firewood. Makes no sense at all.

I averaged around 63mph both coming and going, no real change there. I also use cruise control on the highway, but I'm not sure how or if that affects the fuel mileage. I have noticed with cruise control enabled it tends to resist downshifting or unlocking the converter and just lugs along, whereas just driving with my foot it is much more eager. (perhaps related to the aftermarket "towing" tune).

So in conclusion, I have no conclusion. Can't figure out why I seem to get wildly different fuel mileage calculations.
 
Make sure your fuel cap is venting correctly and your fuel tank is not collapsing.
 
Discussion starter · #29 ·
I know that could affect performance, but it would also potentially affect fuel mileage? I do sometimes hear 'suction' being relieved when I open the cap, though nothing extreme. I was chalking it up to just temperature differences.
 
The volume of the tank changes when it collapses.
That makes it impossible to calculate correct mileage
by how much fuel it takes to fill the tank.
Has happened to me and others.
It's just a possible problem you should remove from the equation.
 
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