ISX 435 CM870 horrible MPG

[Hogleg]

Last tank, measured actual miles (502 miles) and topped off both tanks each time. Took 131.2 gallons. Shows 3.8 MPG. We run 2 lane roads at around 55 with towns every 10 miles or so. We run 70 miles each way loaded to 80K pulling an end dump. I would expect 6 mpg. Our Pete with a mechanical cummins ran 4.8 on this run.

Truck is new to us, bought in Feb. 695K on the clock. 2007 model, egr only. Had the computer read out when we bought it and truck averaged 6.8 over it's lifetime and 6.2 including idle. No red flags on report. Truck runs nice and smooth with no issues.

First thing I did was to replace the map and egr pressure sensors per this site. I have the egr differential sensor also but have not replaced it. Had not measured mileage prior to replacing the sensors.

No codes being set on the dash. I have the BT adapter and a cable (6 pin) but cannot get it to talk to the computer properly to read info with the cummins android app.

Is it possible I caused this with the sensor replacement? How should I diagnose this? I do not believe an overhead has been done on this truck.

Is there a reputable shop in Effingham that can be trusted?

John

[Rawze]

Some info on the crooks that hang out in in effingham...
http://rawze.com/forums/showthread.php?t...9#pid13279

Just be warned.

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Fuel mileage issues are not usually hard to solve on ISX engines. One of the more common ones, besides the obvious boost or CAC leaks for the CM870 is the EGR valve getting mechanically stuck open.

What is the boost peaking? -- Pyro?

When is the last time you used algicide to rid the engine and tanks of algea?

Overhead valve adjustment and overhead cam inspection?

Injector leak test? -- Followed by a cylinder cut-out test to ensure each cylinder can run the engine by itself (running whole engine on only one cylinder at a time).>?

Delta-P replacement?

Inspected the exhaust and muffler for exhaust restrictions?

Pressurized the whole engine for intake, EGR, and exhaust leaks?

Just some starting points. A fuel mileage that bad should be easy to find. it has to be something severe. i have even seen peterbilt and KW trucks that like to get a fuel line leak to the tank on the passenger side right above the exhaust and drip drip drip fuel and it evaporates as soon as it hits the exhaust. Driver complaining about 3 or 4 mpg max.