bad mpg what to do?

872 miles is not a big enough sample to determine anything. Track it for a few weeks at least

 

i've seen loose hose clamps to where you could hear a massive air leak from the hoses. engine still had power. they were local trucks so fuel mileage was the pits anyways.

my isx stalled for a second before kicking in. when the turbo was practically dead.

but your driving a detroit.

diagnostics runs around $200 and is better then playing the guessing game. you've obviously got a problem and need to see the shop anyways. no getting around it.

 

My 09 ISX almost did the same to me, and I ain't no dummy. After buying that POS I learned that the 08 - 09 model years were probably the worst engines ever made. By 2010 they were getting the new DPF technology straightened out but certainly not perfected.

As far as I know I was told by Freightliner that a DD15 455 cannot be turned up. But they are probably the best of the worst. If it were mine I'd have a boost leak down and smoke test run, overhead set, and read it for codes. I'd run it at a speed where you're turning 1300 - 1350RPM at cruise. I'd coast to the scale house or exit ramp as far as possible and shut it off when I get out for more than 5 minutes. I'd check the rolling resistance on the tires because tires with poor rolling rsistance can cause as much as 2 MPG loss. I'd short shift it and allow the torque to get me moving instead of the horsepower. The driver's habits are the number 1 cause of poor fuel mileage and can affect the results by 35% or more. I've had plenty of them and the key word is had. 2 plus MPG and $20,000 plus going up the stacks due to poor driver habits is not acceptable to me.

Fuel mileage gains or losses are rarely attributed to any one thing. It's usually a combination of things that will make or break you at the pump.

 

Park it and push that switch to try to force it to do a regen and let us know. Probably have to hold it for at least 5 seconds. I have my money on it is all a dpf problem ...

 

'09 Series 60's with a DPF are sluggish at best. That motor wasn't designed for it and the one I used to drive was in the shop nearly as often as working. Best bet if you can't ditch it would be to get it turned up as far as possible, raise or eliminate the governor, and get that DPF thoroughly cleaned (after some competent diagnostics are done to figure out the warning light and correct that, of course). Also consider that it was most likely a mega fleet truck at one point and may be carrying around some ECM settings which aren't optimal for your work.

A series 60 is happiest between 1400 and 1900 rpm, mine got best fuel mileage right around 1450. Adding the DPF doesn't change this.

 

I would take it back to dealer , I bought my last truck from Arrow in 2003, they used to have 30 days return policy; change it for a Volvo with D13, 08/09 and manual transmission, they have plenty at Arrow.I have 1,305 ,000 miles on my 780/2008 with original D13,still running , since I got it goes over 8mpg,with average loads; my average this week from Toronto to Laredo and back ,9.2 mpg. I had problems with emission sensors and injector cups , but this motor is amazing on fuel.