Originally Posted by Booyah45828
Lowering rpm should theoretically gain you mileage. But occasionally that gain will be so small it's negligible. Especially if 6th lowers your rpm too much.
If anyone wants to gain fuel mileage, Read this. https://www.prevostcommunity.com/PDF...%20economy.pdf
Read it again if you have to, maybe even a 3rd time. There is a lot of data in there that you should understand if you're wanting good fuel economy.
There is also a lot of info in here if you want to read it. https://www.irv2.com/forums/f124/3126b-mpg-75162.html
But the end result is that 7-9 mpg is about what you should expect to achieve.
my Allison 545 to Allison 1000 (6 speed) install netted me a whole lot of fuel economy gain.. HOWEVER when I first programmed the transmission to get into 6th gear as soon as possible I LOST fuel economy over my program which ran 6th gear completely disabled.. (5th only).. my best MPG currently is allowing my 6th gear to operate during lighter throttle conditions and only over 62 MPH.. my 0 throttle shift-Up to 6th is 63.. my Cruise control operates 6th gear at light load conditions and pulls it out when the cruise drips to 2 below setpoint or engine load reaches 75%..
my bus is geared Too Tall (the opposite of what most skoolies have here)... its important to know when and when not to use it.. the MD3060 has the capability of running 6th or turning it off at your will with the up / down arrow buttons..
know when to use it and when not.. also I will say in Navistar-Land that updating the ECM calibration helps transmission shifting in the E engines.. installing a newer ECM that has a full program update greatly helps the transmission and engine to pick the right gear for the job..
my year 2000 ECM with the original calibration was terrible with the allison 1000.. when I ran it through NavKal(NavKal is the software I subscribe to which allows downloads of programs from Navistar's dealer Cloud network.. yes its expensive.. yes its worth it to me).. it updated the calibration and the base firmware... my shift optimization got better.. when I bought a used year 2004 ECM and loaded my VIN / engine serial number and ran it through NavKal so it had the correct info for my Bus, my shift opimization got to a near perfect state.. in effect navistar had improved their end of things as well.. the ECM I purchased was the current replacement-part number as indicated to me by the navistar dealer.. the original part number had been discontinued and superceded by the new one.. there were things in the newer ECM that didnt get updated by just running it through NavKal.
that said, i still need to gear down from 3.54 to 4.10 to really have the perfect setup in my bus..
** Most diesels like to live a few hundred (500-700) below their governed RPM **
if your computer tells you your engine load factor, its best to run it at 75% or below except when climbing inclines..
I mention all this as lugging down a diesel will result in just as bad of fuel economy as spinning it too fast.. learn your engine.. if you unlocked 6th gear to gain speed because you are running against your RPM governor.. you will gain that speed but will gain no MPG (probably lose it)..
if you enabled 6th so that you can drive the same speed but run the RPMs a few hundred below RPM governor you'll likely gain a good amount of MPGs..
if you enabled 6th when your engine was running already in the "sweet spot" you may very well lose MPGs as you could be lugging the engine in all but perfect conditions..
if your engine sounds and feels Labored it probably is..
the up / down arrow buttons on your shift pad are your friend.. just like driving a stick-shift, pick the right gear for your weight / terrain / WIND-CONDITIONS / speed