bad mpg what to do?

Would be the first place I would look ... I am so happy I do not own a truck anymore with one of those engine (and profit) destroying devices ...

 

All dpf only trucks feel lazy when driving with a load. Don't know that engine very well, but I'd start with the aftertreatment system.........

P.S. My 09 almost put me under.. Find someone local that knows that engine!

 

I have the same story as cat sdp as in my 09 (cat engine KW) also almost put me under.

The dpf back pressure, when not working correctly, or when it fills up, doesn't allow the air through it at all, what this means is your engine can't push it out, your turbo will suffer higher temps, it won't spin freely the way it was designed to. The soot needs somewhere to go. When your dpf plugs it has nowhere else to go but to collect up stream, inside your turbo, inside the engine. The system just plain doesn't work well. The newer trucks, the ones that take def also, seem to function better. Do you run california? Think hard about what emissions requirements you really need to meet to suit your business needs. We are not allowed to recommend the proper "fix" anymore though .....

Two options to "fix" it:
1) - get an older truck that does not come equipped with dpf, or a dpf/def truck if needed for emissions/business purposes.

2) -

End of post.

 

The dpf needs a high enough exhaust temperature to burn the soot. When it fills up and can't burn anymore and the back pressure I was telling you about just keeps building, your turbo can't help the engine make the power needed to get it to the required exhaust temp. The cycle continues and is likely how you got to where you are now.

When I had my cat motor, yeah it is a bit different, but the principle is the same. I was lucky, the engine had begun to fail, just under the wire at 499,000 miles, and cat did a complete rebuild AND put a new dpf on, all under warranty. I figure 30,000-35,000 worth of work there. They said they had never seen an engine with so much soot in it. The truck ran great, ALMOST got 6 mpg, but after 50,000 miles, the same thing happened again. Low power. Low mpg. dpf always wanted to burn, rarely burned completely, was a slug to drive.

I elected to get rid of the entire truck. Where I live, all vehicles must pass an emissions test or they will not sell you licence plates for it. This was my only option to "beat" the emissions (bankrupt) system.

 

Normally if the truck has an MPG problem it is something to do with injectors or the turbo. This is based on my experiences in dispatch. Going into the shop and having a bad injector(s) replaced will fix it or determining why your boost pressure is low and giving zero power. You said your speed is 70? That is far too fast for your gearing. You shouldn't be turning more than 1300 rpm on the highway or you are outside your power band and not operating efficiently. Use this link...http://www.eaton.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/ct_062746.swf. You can further improve your MPG by cruising at 1200 rpm. Turning up the motor wont help your MPG problem. It will only decrease your MPG to have more horsepower. 435 - 450 hp is enough for any highway application 80K or less gross weight. Same goes for the shift points. Don't go much past 1300 unless you are really trying to build power in a hurry. You are just burning fuel going outside your power band.
Again my experience is in dispatch but I know these things have worked in the past. I have had drivers with MPG as low as 5.9, running MPG, in a Cascadia. That is pretty bad. Using some of these tips above they improved in upwards of 7 MPG running MPG.

 

The difference is you were likely dispatching company drivers who don't give a rats behind about the truck they are driving. They will hammer the hell out of it and not think twice. This guy owns the truck and is paying for his own fuel. Higher horsepower does not always mean less mpg. Used properly it can actually mean better mpg. Again - I am not saying you know nothing - it could be the injectors or the turbo, but if it is an injector - the engine will likely run rough or have a misfire, the driver knows something is up. The turbo may be the issue, but it can easily be checked by taking the intake/exhaust sleeves off and checking for free play and inspecting the blades. MPG of 4.5 is much more to do with mechanical problems than driving style. Even your drivers were at 5.9 while hammering the hell of your cascadias, which likely had detroits in them also. AND - the cascadia didn't come before 2008 I think, meaning all of them on the road would also have DPF's. More than driving style problem here.

 

Correct and being an owner op does not always mean you are aware of your engine parameters and where it is most efficient. That is why I included the link. Seeing as he mentioned he was driving 70 that already stands out as a big problem. If there is one driver related issue, driving too fast the gearing, there could possibly be other issues. Those should be addressed first before one would begin looking at Mechanical issues or hating on the DPF or EGR. When I worked at JB Hunt in 2006 they were running 435 hp century trucks with 10 speeds getting consistent MPG of 6.35 - 6.5. The biggest differences in MPG were driver related unless there really was a mechanical problem.
More horse can definitely be a good thing but as I said 435-450 hp is enough if you are 80K or less. Some of the newer trucks from Volvo and Mack are beginning to push 505 ho motors with their automated trans allowing to maintain speed up hill at only 1050 rpm. More hp I suppose could lead to greater MPG and the problem is that normally when you have more hp you tend to over use that power. Kind of like trying to drive a corvette for maximum fuel economy over your old honda civic. The power is there and you are going to use it.