Try using clean Boost MaxxI bought my truck in July 2012. Pretty much been battling a fuel mileage issue since then.
07 Century, 14L EGR Series 60, 13 spd, 3.42 Meritor 14X rearends.
Mind you, my mileage isn't horrible, it's 6.2 mpg for an annual average. All miles actual and all fuel counted for the year. My issues is the RANGE. I was seeing from a low of like 4.6 to a high of 8.87.
Things I have done.
3-axle and 5-axle alignment.
Gotten rid of ALL recaps and gone to GY 399L steers, Firestone FD695+ drives, BFG 720 drives and Double coin trailer tires on the trailer. All virgins. No recaps.
Exhaust Manifold gasket replaced. After the first Manifold gasket replacement, turns out my silicon boots between the Turbo and CAC were leaking. Replaced both of them with all new clamps.
Had the ECM tuned on a chassis dyno. Putting 550 hp and 2060 Ft-lb torque to the ground. Yop, it'll pull.
Had the overhead ran. No significant improvement.
replaced the ECM to firewall wire harness. If you drive a Freightliner, I'd pay REAL close attention to it. There's a 10 ga battery positive wire that runs through this bundle. The sheathing had rubbed through large areas of wiring where it makes sharp bends over the ECM and the starter. It WILL shut your truck down on the side of the road, and if that BAT+ wire rubs and shorts, I can see it being a fire hazard.
Found out my CAC was seriously leaking. Took some windex and just fast idle to find this issue. I had it in 4 times to have it tested for a bad CAC. No one found it.
Replaced the power divider. Input shaft bearings were TOAST. This was kind of suspected back in July after I got the truck home. My mechanic had gone in and tightened up the input yoke on the power divider. We just kind of ran it and kept an eye on things but it lasted 85,000 miles after I bought it.
Serious fuel issues over the winter. In Nov/Dec, I used 42 fuel filters. It took a 16 OZ Kill 'em, two 32 oz
CLEAR-DIESEL® Fuel & Tank Cleaner and one 80 oz bottle of Emergency 911. I have been averaging 28,000 miles on a filter now since I put in that fuel cocktail to 240 gallons. Prior to that, about 7,000 to 9,000 miles. I even made a filter setup so I could try and clean the fuel at night after driving for the day.
Replaced the entire exhaust manifold with new. Center section was showing hairline cracks and there was soot behind the manifold. Turns out it was the EGR to Manifold joint that was leaking.
I pulled my map sensor out and decided to clean it with ether. Seems to have helped. Since it helped, I just changed both the MAP and the boost sensors.
I was starting to show similar behavior to what happened the first time I replaced the exh man gasket so I checked all my clamps again. Yop, two clamps loose like 6 full turns and leaking. Big ol' bubbles blowing out.
As a result of the manifold replacement, I came down Bozeman pass in Bozeman MT and the exhaust pipe came off the turbo. I have no clue why other than there was NO nut on the turbo clamp. The pipe itself you could see was damaged from being tightened like it was installed incorrectly.
In Mt Vernon WA, I noticed I was up in fuel mileage again. I got to thinking...All my best mileages occurred in Boston, Florida and now Seattle areas. What do ALL those areas have in common compared to running in MN and the upper plains? Sea level vs 900-1000 ft in elevation. I pulled into the Freightliner dealership and asked them about if they could map the range on the Baro sensor. Yop, you guessed it..."deer in the headlight" look. "Two hour minimum to hook up the computer. $250 charge." And how much is a sensor? $113. Bought the sensor and put it in.
Fueled in Sumner WA and drove to McMinnville Or to Ontario OR. Gross weight, 70,0000. 7.21 MPG Hmmm.....Lot of 2500 ft pulls between 2000 to 4400 ft there. I remember 4 pulls at least in there.
Ontario OR to Laramie WY 6.54 mpg. Hmmmm... You climb to 7800 feet from 4000 feet in Ontario. SEVERAL times too. Three Sisters on I80 are in there too.
Today's fuel mileage according to the dash sucked. But across NE, there was a 20-40 mph cross wind at 90 degrees. I was still above 6.4 mpg according to the dash. I'll be fueling on Tuesday sometime and have a better idea what the mileage is.
Two things. I am pulling hills in a gear higher than I had before. The truck hasn't gone below 6.1 MPG on the dash yet. In the crosswinds I had coming across NE today, I would have been low 5, high 4's for mileage easy.
In a nut shell.....
replace your CAC when needed.
No exhaust or turbo leakes. CRITICAL here.
Replace fuel and air filters on a regular basis.
If you can't get any other things to better your mileage, consider $200 worth of sensors. MAP, BARO and boost sensors. They get dirty and seem to really make a difference.
So what do these sensors do?
Boost sensor is obvious. It tells you the level of boost the engine is seeing.
MAP sensor tells the engine how much load is on the engine. Compares the manifold pressure to atmosphere.
BARO sensor basically is telling the ecm what the altitude is. Changes the fuel and timing curves as a result.
I was able to find this in the EPA 04 EGR tech manual. Good luck it would seem getting a service shop to understand it.
Call talk to Chuck Rice
(214) 366-2711 W
(214) 316-2453 M
I've been using for 14 months now my MPG's are 11% higher than before using it my overall all is 8.1 and high 8's-mid 9's in summer average load 35K