Power and MPG Trouble....Not Sure??

[Joe W]

I stumbled accross this site about a month ago while looking for performance mods information. After reading about all the posts relating to power or milage I started thinking I had something wrong. The truck had pretty bad turbo lag but once it got wound up it made plenty of power. I just thought it was me at that point. What really got me was hearing about all this great milage everyone is getting (compared to mine). As an example, last weekend I towed a 5000 pound boat about 200 miles on mostly level highway running 70-80 mph and got right on 10 mpg. If I'm going through a town running around 35 plus a few lights here and there I can get 11-12. Empty on the highway running at 65 with no hills I get around 14. Running my normal 80ish speed we're talking 11-12. EMPTY! Slower speeds and through some towns I see 13-14. I was just pulling around 8000 pounds on the highway at 65 and around 2000 rpms and the slightest grade makes the thing want to downshift and crank like a gas motor. It reminds me of the V10 used to have.

I took it to the dealer last fall for reprogramming over a rough idle condition. It felt like it lost a bunch of power after that but I haven't towed anything over the winter so I wasn't too sure. I took it back a few weeks ago and they found and replaced a cracked Y-pipe so I was losing a little boost. Also gave it the lastest programming. This fixed my turbo lag. At low speeds it's plenty snappy now and the turbo whistles and off you go. It's at cruising speeds that it feels like a slug and the milage sucks. I know I lost a little gear when I went to 33" tires but I can't believe this is normal. A buddy of mine has an 03 7.3 CC long box duelly with a 6" lift and 35" tires and pulling a camper last weekend to the same place he got 14 without a speedometer correction.

I've had the truck for almost 3 years now. It seems to me when it was new I remember getting 15ish on the highway and 13.5 local driving. Is it possible that all this is completely normal for a 6.0 and I'm just figuring it out?

[2006KR]

What's the rear-end ratio? Makes a difference. Also, the 80+ doesn't help. A close friend has an F250 with the 3.73 gears, and 2000 RPM on his is just a tad over 70. Your best milage is going to happen when you keep the RPM's below 2000 (that is your peak torque RPM). Larger diameter tires are going to hurt as it makes the engine work harder to get you to speed and harder work = more fuel needed. They also have an impact on performance. Ideally, if you go to larger diameter tires, you need to lower the gear ratio to compensate for them ... the down side, now you just lowered the speed at which you can run at 2000 RPM.

A steady foot and where possible, cruise control really helps. Example: just finished up a 3000 mile vacation pulling my FW. Left Memphis, spent a few days just north of Hope AR (Crater of Diamonds State Park), next on to Austin TX for a few days, then back home to trim the 'forrest' that is normally called grass, then to Gatlinburg TN for a few days then back home. Experienced everything from flat country to 5% grades and averaged 11.7 for the trip ... tried to keep my speed between 60 and 65 (with the tow boss 61MPH is 2000RPM). Decent milage is possible ... I say decent as I think 11MPG dragging an almost 14K of trailer around is decent.

[trrun]

You can add a more open intake and upsize your exhaust to 4". I have a 7.3 and with an AFE stage 2 and a 4" turbo back exhaust netted my 2+ MPG. Then i added a good chip with a good 40 tow and 80 econo setting now with the 80 setting running empty i get 17.5 (hand calc.) where as before the mods i was lucky to see 13.5 empty on the highway running 75 about 2200 rpm. I have 4.10 gears and its a 8200lb truck. I don't think what your gettings all that bad really. These are heavy trucks and you loose very little in comparision to the gas motor equivelant. While towing my grandfathers 460 FI gas motor gets 8mpg empty and 6 pulling about 8,000 lbs.
Tim

[nathan]

I have a 99 7.3 may not compare to your truck. But every one I talk to says the get 17-20 mpg and the best I get is 12-14 with out any load. It seems like the harder I run the truck the better milage I can get.

[mschn99]

Have you re calculated your milage since the Y pipe change, loss of turbo boost will also cause a dropp in fuel economy.....

[Joe W]

Here's the latest. The technician felt the vanes in the turbo might be sticking under certain conditions so they put a new turbo in it. After several tanks of fuel and letting the computer do the "relearn" thing, my very best full tank mileage (empty) was 14.6 mpg. The norm is around 13.5 mpg. The best I can do pulling the 5K boat is 10-11 mpg. Driving any more conservative would be unrealistic for me. 60-65 on the highway is painful enough.

I put a 4" Mangaflow system on it and if it's done anything at all for it, I sure can't tell..... Except for the obnoxious turbo whistle at part throttle. Yeah, I thought it sounded cool at first but it got annoying quick.

I had my finger on the "buy now" button for a Bully Dog Triple Dog but then got to reading all the customer feedback on the web. Nearly all of the guys claiming substantial gains in fuel economy are Cummins guys. I'm starting to feel like I'm throwing good money after bad.

I have 3.73 gears and a 33.5 inch tire. I've checked my speedo with radar, GPS and distance markers and it's right on the money. The dealer blames poor fuel but I doubt it. It just IS what it is. Thanks for the feedback.

[BUKWAKR]

I Have A 05 F-250 Supercab Longbed All I Have Is A Banks Monster Exhuast I'm Getting 15 Around Town And 20 - 21.5 On The Highway Thats No B.si Did The Calcs. Going Out To Pa Filled Up Went 200 Miles Burned 9.3 Gals . The Way I Check Is Fill It Up Reset Trip Run To You Need Fuel Fill It Up Record The Gals. Then Divide By Miles
As For The Tires Larger Tires Should Give You Better Mpg On The Highway Since A Larger Tire Covers More Distance Per Revolutoin


Darrell

[mschn99]

Originally Posted by BUKWAKR

As For The Tires Larger Tires Should Give You Better Mpg On The Highway Since A Larger Tire Covers More Distance Per Revolutoin

That is COMPLETELY untrue. Yes, the tire will travel further per revalution, which will make your odometer also say you went less miles than you actually did, thus giving the illusion of better fuel economy if your speedo is not recalibrated for the larger tires, BUT in fact the extra power it takes to turn the larger diameter tires is more than what they gain you by going further each revelution. There is NO way a larger tire will ever raise your fuel economy, even at cruising speeds.......Marc

[Bill M.]

Originally Posted by Joe W

I stumbled accross this site about a month ago while looking for performance mods information. After reading about all the posts relating to power or milage I started thinking I had something wrong. The truck had pretty bad turbo lag but once it got wound up it made plenty of power. I just thought it was me at that point. What really got me was hearing about all this great milage everyone is getting (compared to mine). As an example, last weekend I towed a 5000 pound boat about 200 miles on mostly level highway running 70-80 mph and got right on 10 mpg. If I'm going through a town running around 35 plus a few lights here and there I can get 11-12. Empty on the highway running at 65 with no hills I get around 14. Running my normal 80ish speed we're talking 11-12. EMPTY! Slower speeds and through some towns I see 13-14. I was just pulling around 8000 pounds on the highway at 65 and around 2000 rpms and the slightest grade makes the thing want to downshift and crank like a gas motor. It reminds me of the V10 used to have.

I took it to the dealer last fall for reprogramming over a rough idle condition. It felt like it lost a bunch of power after that but I haven't towed anything over the winter so I wasn't too sure. I took it back a few weeks ago and they found and replaced a cracked Y-pipe so I was losing a little boost. Also gave it the lastest programming. This fixed my turbo lag. At low speeds it's plenty snappy now and the turbo whistles and off you go. It's at cruising speeds that it feels like a slug and the milage sucks. I know I lost a little gear when I went to 33" tires but I can't believe this is normal. A buddy of mine has an 03 7.3 CC long box duelly with a 6" lift and 35" tires and pulling a camper last weekend to the same place he got 14 without a speedometer correction.

I've had the truck for almost 3 years now. It seems to me when it was new I remember getting 15ish on the highway and 13.5 local driving. Is it possible that all this is completely normal for a 6.0 and I'm just figuring it out?

I am also new to this site. I was thinking about replacing my 1999 diesel and was surprised to see so many people complaining about fuel ecomony. I do not drive my truck as hard as you do and I do get quite a bit better fuel economy. I had a about a 9k travel trailer that I would get about 13-14 mpg on flat country and 9 to 10 in hilly terrain. I usually get about 17-19 mpg unloaded at about 70 mph, any faster and it starts dropping. The thing to keep in mind about fuel economy is as they de-sulfur diesel your fuel economy will suffer. People who travel in Mexico are always surprised at the fuel economy they receive. There is of course no de-sulfurization of diesel in Mexico. Most receive a minimum of 10 percent better fuel economy. After reading about some of the problems with the 6.0, I think I will be hanging on to my old 7.3 for a while.