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best mpg
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=70675		 Page 1 of 1
Author:  cdubs [ Sat Sep 01, 2012 4:28 pm ]
Post subject:  best mpg
Just a question for all of u that have been driving your crd's much longer than I have. But where is the sweet spot on these engines for mpg. I find myself trying to cruise around 1700-1800 rpm but don't know if that is the best cruising speed.
Thanks
Author:  Rixram [ Sat Sep 01, 2012 9:39 pm ]
Post subject:  Re: best mpg
If you have the stock TCM and ECM, then know that the transmission shifts into 5th gear fully locked torque-converter at 62 mph, and will hold that gear/lock down to 58 mph (indicated on speedo).

If you upgrade to Green Diesel's ECO-tune ECM and upgraded TCM, then it will shift to 5th/lockup at 58 (versus 62) and downshift at 50-52 mph. I can run at about 53 mph at around 1,400 revs. Of course, folks behind me are going insane when I'm at that speed, but that's their "effing" problem.

Please be advised that all speeds listed above are with the factory undersized 225/75R16 tires (speedo reads fast by about 4-5%. When I have 60 mph indicated on my speedo, GPS holds me at about 57 mph).
Author:  papaindigo [ Sun Sep 02, 2012 3:46 am ]
Post subject:  Re: best mpg
As mph/rpm goes up mpg goes down within limits. I suspect the best mpg spot is the lowest mph/rpm where the tranny will hold 5th full lockup and that spot depends on F-37 status or what GDE tranny tune you have. IMHO the best spot for mpg and not going nuts driving slow is ca. 1800 rpm which under all conditions and tunes will put you in 5th full lockup and right about 62 mph GPS corrected on stock size tires. I'm not sure what other tire diameters, not widths, would do though.
Author:  striperman36 [ Sun Sep 02, 2012 10:14 am ]
Post subject:  Re: best mpg
I try to stay under 2000 all the time, that's about 68, after I pass RixRam.
Author:  cdubs [ Sun Sep 02, 2012 4:40 pm ]
Post subject:  Re: best mpg
That's about what I was expecting to hear, I can keep it at about 1700 or a hair less still holding 5th gear. that puts me at about 60 on my speedo or about 57-58 on the gps, so far it has been neting me about 27 mpg after corrections for the odo being off about 5% around 26 without the correction.
Author:  ATXKJ [ Mon Sep 03, 2012 6:10 pm ]
Post subject:  Re: best mpg
in general the slowest speed, that you can hold the highest gear.....

I got 29mpg - with a lift/ 245/75/16 AT's full armor and steel bumpers - running just below 65......
Author:  cevans [ Wed Sep 05, 2012 2:43 pm ]
Post subject:  Re: best mpg
I've had 32mpg+ tanks when cruising over 70 mph. I had a few near 35mpg with 62-68 driving, but I think that at under 62 mph you are out of the efficiency window of the motor.
Author:  mk38tech [ Thu Sep 06, 2012 12:44 pm ]
Post subject:  Re: best mpg
cevans wrote:
I've had 32mpg+ tanks when cruising over 70 mph. I had a few near 35mpg with 62-68 driving, but I think that at under 62 mph you are out of the efficiency window of the motor.


i think you are a little over on the speed. for mine, i also have the eco and full tq from GDE. 225 tires. ive made many trips of exactly 114 miles. ive made this trip more times than i can count. ive tried cruise control in 50, 55, 60, and 65 mph as well as free footin it at the same speeds. cruise control doesnt do anything except waste fuel in most cases because your more than likely going to have some small vac leak, or if you live in the north or around mountains, constant fuel waste due to going up and down hills. I live in north florida. granted theres a lot of traffic here, i only responded to this because of the fact of where i live. i have no spare tire on the jeep, and stock exhaust with an open air filter intake from advance auto. i also run a little 2 stroke from time to time. from what ive noticed about MINE, is that the closer i stay to 1500 rpm, the more efficient i am. with the same 114 mile trip, ive seen numbers from 41 to 44 mpg many many times. usually keeping my speed strictly to 50-55 mph. now that im submitting this your going to see people say "oh BLAH BLAH BLAH, THATS IMPOSSIBLE". some people are idiots. the numbers are real, the jeep is real, and the heat here in florida is definately real. i buy chevron fuels religiously since its hard to trust anyone else on fuel especially gasoline. maybe I overinflate my tires a bit, and im fairly thin at 160 lbs. the crd KJ weighs about 4700 lbs? im trying to figure out why you guys are getting such low numbers. only thing i can think of is the location. im going to do some custom exhaust work this weekend and start the drawings for a little meth injection. imagine what the numbers could be if there was a decent aftermarket for these amazing things.
Author:  ChooChooman74 [ Thu Sep 06, 2012 12:50 pm ]
Post subject:  Re: best mpg
What does a vacuum leak have to do with fuel mileage and cruise control? Our throttle is all electronic.

Sent from my DROID BIONIC using Tapatalk 2
Author:  mk38tech [ Thu Sep 06, 2012 2:35 pm ]
Post subject:  Re: best mpg
ChooChooman74 wrote:
What does a vacuum leak have to do with fuel mileage and cruise control? Our throttle is all electronic.

Sent from my DROID BIONIC using Tapatalk 2



referring to vacuum actuated vehicles like my dodge outside. no matter what controls the cruise, its always going to be less efficient than foot throttle. unless the person sucks at controlling their own vehicle and controlling their foot. in that case they might have tourettes syndrome. electronic is the same thing, its always going to be moving your rpm up and down without your control especially up and down hills
Author:  ChooChooman74 [ Thu Sep 06, 2012 4:03 pm ]
Post subject:  Re: best mpg
I admit, the best MPG people do control the throttle. I can't do that. I get into 5th and back off to 1700rpms and set the cruise. It stays there on my Jeep. I am happy with my mid 30s.

Sent from my DROID BIONIC using Tapatalk 2
Author:  DNR [ Sun Sep 09, 2012 9:39 am ]
Post subject:  Re: best mpg
most of the time i stay local no highways, but even cruising slow around 55 on the highway or the normal 70 i get average 21 mpg 23 on best. With eco tune and stock lift and tires.
Author:  Dennis MacGyver [ Sun Sep 09, 2012 12:29 pm ]
Post subject:  Re: best mpg
Just found out yesterday that when you direct the air flow HVAC to the floor only it kicks on the AC to prevent interior window fogging. Yea right. Here in Nevada our humidity is usually <10%. Having the AC on has to cut into our mileage.

I'll be doing the following mod to turn the AC function of the heater off tomorrow. This mod makes the AC come on when YOU choose it should be on, not when some engineer "feels" it should be on.

viewtopic.php?t=6042&highlight=compressor+settings
Picture: http://img354.imageshack.us/img354/5545/hvacmodfo9.jpg
Author:  DNR [ Thu Sep 13, 2012 6:55 pm ]
Post subject:  Re: best mpg
i thought it came on with the defrost...to keep the pump lubricated in the winter when you don't use the a/c
Author:  Dennis MacGyver [ Thu Sep 13, 2012 7:09 pm ]
Post subject:  Re: best mpg
DNR wrote:
i thought it came on with the defrost...to keep the pump lubricated in the winter when you don't use the a/c


The problem I have with it is that it, the AC, also comes on when you direct the flow to the floor, yes the floor (how stupid is that). In the winter should I need to defrost, since I'm an adult (with at least 50% brain capacity), I can push the AC button myself (thank you Jeep eng. dept.). PS. In Nevada, our humidity level is usually <10%.
Author:  papaindigo [ Fri Sep 14, 2012 7:46 am ]
Post subject:  Re: best mpg
No point in throwing rocks at DCJ engineering on the AC engaging on the floor and defrost settings as that's a common industry practice as I know Ford does the exact same thing. IIRC at least on the defrost setting the AC engages to reduce ambient humidity and defrost the windows guicker. In some vehicles, don't know about the KJ, the AC compressor also engages in the recirculate mode for the same reason.

There are a couple of work arounds one defeats that completely and another simply installs a switch so you can select to use the AC compressor or not.
Author:  dirtmover [ Fri Sep 14, 2012 12:48 pm ]
Post subject:  Re: best mpg
papaindigo wrote:
No point in throwing rocks at DCJ engineering on the AC engaging on the floor and defrost settings as that's a common industry practice as I know Ford does the exact same thing. IIRC at least on the defrost setting the AC engages to reduce ambient humidity and defrost the windows guicker. In some vehicles, don't know about the KJ, the AC compressor also engages in the recirculate mode for the same reason.

There are a couple of work arounds one defeats that completely and another simply installs a switch so you can select to use the AC compressor or not.


Common industry practice doesn't necessarily mean best practice. Some forward thinking, a couple of bucks on a humidity sensor and a few lines of code would ensure that the compressor only comes on when cooling or dehumidification is required. A few more lines of code could kick in the compressor for a few minutes if it hasn't engaged in a few days/weeks.

Of course some thought and a couple of dollars spent on an optimal solution is not what we've come to expect from Chrysler :(
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