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Diesel Fuel Milage: Problem or Not?

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Posted by: motohead00---------------------

This was posted in a diesel forum as well:

My question is this, according to reading posts about fuel consumption with 315/75/16 tires, my fuel milage is lacking. The truck is a 2001 4x4 CC PSD with 3.73 and 2" add-a-leafs and small blocks in the rear.

My fuel milage when the truck was new was 15 to 17 mpg empty and 13 to 15 mpg pulling a 6x12 enclosed trailer with dirtbikes in it. According to some reading, I wasn't getting terrific milage, but wasn't horribly dissatisfied either.

About 15000 miles ago I installed a DiabloSport Chip labeled 4 bank X14. It was programmed with the lower power setting (50 -60 hp?). The power increase was noticed immediately, but I was hoping to gain some fuel milage out of the upgrade as well. With the new found power, my right foot may have gotten "heavier" so I didn't realize any MPG increase. In fact, the MPG was down 1 to 2 MPG. No big deal I thought. I just put on the 285/75/16 tires and the 2 inch lift. Maybe that was the cause.

Well, after a while, the milage decreased another 1 to 2 MPG. Attributed that to wintertime etc... even though I live in Louisiana. Then I installed the 315/75/16 tires and saw another 1 MPG drop.

One thing to note was that after installing the chip, occasionally when accellerating/merging into traffic or sometime hard accelleration with a trailer, the tranny or truck would "shudder" or try to shift 1 or 2 times more when shifting up to high. I have done some reading today and wonder if this is the compressor surge or flutter that I have just read about. It only does it under load or acceleration and shifting to high. (?) Note that my trailer loads with this vehicle have never been more than the 6x12 enclosed trailer with 1500 or lbs. of bikes and gear.

Fuel milage was now down to about 11 to 12 mpg city/hwy and 10 to 11 with the light towing that I do. I know this is more truck than I need now that I sold my 76 Bronco and no longer need this much truck, but I really do like it.

Anyway, last week, I went to Reno, by way of KC, MO and through the mountains to Denver, Wy, Ut and finally Nv. Fuel milage with 4 bikes and gear was worst of 8 and best of 10 MPG. Figure in larger tires at approx. 10.6% and figure best was actually 11 mpg.

So, today, for a check, I pull out the chip and made a 200 mile round trip and checked milage. The first 100 miles was without the trailer, and correcting for tire size, without the trailer on the way up was almost 14 mpg. Picked up the trailer with one bike and brought it back from the riding area where I left it at our clubhouse 2 days ago and returned and checked the milage correcting for tire size was 10 MPG.

I called the dealer that I bought the chip from, told him of my experince with the shifting and the fuel milage. He suggested that it might be a problem with my torque converter that was magnified by the increased power provided by the chip.

Does this sound reasonable, do my MPG figure sound reasonable or not with the way the truck is currently equipped? What should I check, or should I take it to the dealer for inspection. The shop/owner where I bought the chip said he could make sure any evidence of the chip was removed before taking it in to avoid any potential warranty problems as well.

Now that I have written a small novel, I am hoping the someone with some expertise here can provide some input and info because I really don't want to sell my truck and feel that I should be doing better milage wise. I can't see myself buying one of the other two brands, so please any other brand loyal guys, save you breath in that category. This is minor to the other problems I have had with other brands.

Thanks in advance for any assistance you can provide.

Randy


Posted by: bsmith---------------------

If it helps I'm averging 18.3 in my Dodge (I have a computer that keeps track for me!)

I bet the lift doesn't help, do you have a visor? I had a Lund visor on my last Dodge deisel and it cost me 1-2 mpg's.


Posted by: Patman---------------------

Sounds reasonable to me. That a lot of truck and with it being a 4x4 with a lift and bigger tires that will do nothing but cost you fuel mileage. I've heard the Diablo chips are not the best as far as mileage gains but can't say I have any experience myself with one. I run 285's on my 4x2 SC that's a 6spd and consistantly get 18.5-20mpg daily and when I hit a highway trip it goes into the 21-22.5 range (265s). The only modifications I run are a PowerProgrammer III, Amsoil dual bypass filtration system with Amsoil lube front to back and an Amsoil oiled foam air filter. I did get a little better mileage before the 285's when it had 265's but maybe 1mpg if that. I've pulled my JD tractor 120 miles each way on my tandel axle flat bed and seen it drop to the 16mpg range. Winter blend fuel will flat out kill mileage so I suspect that was a big part of your drop on the Reno trip.


Posted by: motohead00---------------------

If it helps I'm averging 18.3 in my Dodge ===> BSmith, that's just it, the other guys with similar Fords are getting figures like yours. I am hoping to be able to do the same.

Further experimentation today. Put the 285s back on and made a round trip to Baton Rouge and back. Approx. 180 miles round trip with city and highway driving and average about 14.5 mpg.

Think I will still take it to the dealer just for some peace of mind, just because lots of folks at the the dieselstop.com seem to be doing better than mine anyway. She's still under warranty at just under 25000 miles. See if there might be something I am missing.

Patman, who do you by your Amsoil products from? I was thinking about signing up for the distributorship deal through them if nothing else but for the price benefit. Did the Amsoil products seem to help your milage?

Thanks,
Randy


Posted by: gasgasman---------------------

With the bigger tires the speedometer will be off. You can have the PCM reflashed to the bigger tire size.

After you pull the chip out, you need to reset the PCM. It has an "adaptive strategy". The PCM "learns" your driving habits and adjusts the trans and engine controls accordingly. To perform a reset, disconnect both batteries for 15min.


Posted by: motohead00---------------------

Quote:
Originally posted by gasgasman
With the bigger tires the speedometer will be off. You can have the PCM reflashed to the bigger tire size.

After you pull the chip out, you need to reset the PCM. It has an "adaptive strategy". The PCM "learns" your driving habits and adjusts the trans and engine controls accordingly. To perform a reset, disconnect both batteries for 15min.


Thanks for the heads up. I have the info for the Svc tech to re-flash for bigger tires in case he/(she?) hasn't done it. As for the resetting the PCM, thanks for the info... didn't know that one. Will do that tomorrow morning.

rla


Posted by: gasgasman---------------------

No problem.
If you're in the Houston area-during the week, I can reflash the PCM for you.


Posted by: motohead00---------------------

I will not be in the area for another 2 weeks. I may just be there around March 10th, but I am not sure yet. If I am coming, I will contact you, and thanks for the offer!

rla


Posted by: Bill Beard---------------------

I get 14-15 MPG on the highway with my '99 PS, 373 gears and larger tires. I run pretty fast on the highway though (80-85 a lot @ 2400 RPM). When I take my 5th wheel out (about 10,000 GVW) I get about 10 MPG. I have a chip (don't remember who's) but only noticed gains in HP and Torque. A couple friends have them too and they don't get any better mileage. So I don't think your mileage is that far off. If anyone with a PS tells you they get 18 or so MPG, either they are lying or drive like an old lady.


Posted by: motohead00---------------------

Quote:
Originally posted by Bill Beard
If anyone with a PS tells you they get 18 or so MPG, either they are lying or drive like an old lady.


LOL!!! I hope that is the case! I still wonder about some of the mods I have read to increase fuel milage. I might give them a try.

Thanks for the input.

rla


Posted by: oldguy---------------------

I have a 2000 F250 PSD 2 wheel drive with the 6 speed and in summer :
hwy/city 22-23/20 with toybox (6000lbs) 19/?
winter 20/16 with toybox 17/?

I know I gain from the 2 wheel and the stick but I wouldn't think more then 4 or 5 at most.


Posted by: G. Gearloose---------------------

I think its the stick. My bud with a similar vintage 4wd 250 and 6-speed gets about 2-23 hwy, 18 city, about 20 average. Thats with 33" bfg all-terrains, no chip.
I've driven both an auto and this one, and I'd say the power between 1200 and 1900 rpm is entirely wasted with that automatic. Gm's 4l80 was much better matched to diesel power.


Posted by: Patman---------------------

Quote:
Originally posted by Bill Beard
If anyone with a PS tells you they get 18 or so MPG, either they are lying or drive like an old lady.

Well sorry to disappoint ya' but I'm not a little old lady nor a liar. Granted I do have a 6spd with the 3.73's and most of my travel is highway but, the facts remain.

BTW GasGasMan rocks!


Posted by: gasgasman---------------------

THANKS Patman.
I luv you man!!



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