(06-25-2018 )VNL670 Wrote:  Good evening everyone. I am an O/O in need of some serious help or advice. After totaling my 2007 VNL670 with a Cummins CM870, I bought a month ago a 2014 VNL670 (VIN:157174) with a 525 HP ISX CM2350 (ESN 79646948) and a manual 13 speed. It had a CIL when I bought it. I took it to the shop in Venus, TX and here is what has been done so far, but not on the same trip. Please keep in mind that the truck started to lose MPGs around 2 - 3 weeks ago.

1. Oil change, air & fuel filters. (complete PM)
2. Oil pan gasket
3. Upgrade fuel pump inner rods from ceramic to metal with a rebuilt head unit from Cummins.
4. Baked & cleaned both DOC and DPF filter.
5. New injector DEF doser and gasket.
6. All new DEF sensors. (All sensors have been changed except the ammonia sensor on SCR)
7. New Delta-P sensor.
8. New I-map sensor
9. Exhaust gas pressure sensor (Close to the thermostat).
10. Fuel rail pressure sensor.

The issue is that after all these repairs the truck is only getting around 4.5 mpg (at the pump) cruising at 68 mph at 1400 rpm with light loads (50000lb - 60000lb) all in the South and Midwest. Currently there are no CIL on the dash or any messages. Boost gets to 35-37 on the gauge between gears and shifting or up-hill. Doesn't over heat and does not run hot like my old CM870. I fill up the DEF tank every 4-5 fuel fill-ups or roughly 4000 mile (give or take). It drives fine but just using a LOT of fuel. Ask me anything you want and if you need pictures, let me know. Any advice on what else to replace is highly appreciated.

(06-26-2018 )Hammerhead Wrote:  

(06-25-2018 )VNL670 Wrote:  Good evening everyone. I am an O/O in need of some serious help or advice. After totaling my 2007 VNL670 with a Cummins CM870, I bought a month ago a 2014 VNL670 (VIN:157174) with a 525 HP ISX CM2350 (ESN 79646948) and a manual 13 speed. It had a CIL when I bought it. I took it to the shop in Venus, TX and here is what has been done so far, but not on the same trip. Please keep in mind that the truck started to lose MPGs around 2 - 3 weeks ago.

1. Oil change, air & fuel filters. (complete PM)
2. Oil pan gasket
3. Upgrade fuel pump inner rods from ceramic to metal with a rebuilt head unit from Cummins.
4. Baked & cleaned both DOC and DPF filter.
5. New injector DEF doser and gasket.
6. All new DEF sensors. (All sensors have been changed except the ammonia sensor on SCR)
7. New Delta-P sensor.
8. New I-map sensor
9. Exhaust gas pressure sensor (Close to the thermostat).
10. Fuel rail pressure sensor.

The issue is that after all these repairs the truck is only getting around 4.5 mpg (at the pump) cruising at 68 mph at 1400 rpm with light loads (50000lb - 60000lb) all in the South and Midwest. Currently there are no CIL on the dash or any messages. Boost gets to 35-37 on the gauge between gears and shifting or up-hill. Doesn't over heat and does not run hot like my old CM870. I fill up the DEF tank every 4-5 fuel fill-ups or roughly 4000 mile (give or take). It drives fine but just using a LOT of fuel. Ask me anything you want and if you need pictures, let me know. Any advice on what else to replace is highly appreciated.

These are the two issues that jump out at me.
First, great fuel mileage cannot be achieved at high speeds, but regardless, you should be getting better than you are.
Which leads to something very obvious, a CM2350 SHOULD NOT BE ANYWHENEAR THIS MUCH BOOST! Verify this is correct, and have someone who knows what they are doing verify you have the correct programming in that thing BEFORE it's too late.

(06-26-2018 )DLC Wrote:  One thing I tell guys to do is to take a windex(spray bottle) filled with some dish soap and water and spray down all your intercooler connections. Rev engine to 1200rpms or so and spray all your intercooler connections. I find leaks on most of the ISX/QSX equipped machines I see. IH trucks are bad with their shrink clamps. I'll spray down intercooler too but haven't found any leaky ones yet. It may not be your silver bullet but it's easy and cheap to do. Someone will chime in and say he's got lots of boost and won't have a leak don't bother checking. Please just check and there's one thing off the list.

(06-26-2018 )Rawze Wrote:  Just for reference there hammerhead, on a 2350 with egr still active, a couple psi higher than a demandated truck if it is using a lot of egr gas.


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What is the rear ratio of the truck? What is the mileage? - I did not see it mentioned.

Like hammerhead has said,.. has anyone verified that the truck has the correct program in it based on the engine ser#?. I.E.> Make sure someone did not "up the hp".

* Has anyone bothered to look at the decomp tube and verify it is not partially clogged? Reference: http://rawze.com/forums/showthread.php?tid=283&pid=1807#pid1807

* Has anyone bothered to see if the Doser injector behind the turbo is leaking fuel?

* Has anyone bothered to pressurize the CAC and check it for leaks? -- How about pressurizing the entire engine between the intake filter and the back of the turbo and checking it for leaks as well?

* Does the truck have an after-market CAC unit on it? - Many brands of after-market CAC uints are very restrictive and cause fuel mileage losses.

* Does it have an after-market EGR cooler on it? -- Same thing, they can rob you of fuel mileage and in fact many have even caused engine damage due to excessive egr temps.

* Anyone bothered to pressurize the fuel tanks and check the lines for leaks?

* Does it pass a leak-down test? Reference: https://youtu.be/eH9GRkeozTM

* Anyone bother to flow-test or even inspect the the SCR unit for clogging?

* Anyone bothered to do valve adjustment?

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It the mean time ...

Like Hammerhead said, slowing down to 63~ish will help -- A LOT!. So will driving by your boost gauge and limiting boost to about 15 psi or so as a good start. I am not saying this as a replacement to any fuel mileage loss problems the engine or truck may have,.. but it will definitely help mitigate losses. This is especially true while you figure out how to get the fuel mileage back up to normal levels. Better driving habits always lead to higher profits and less down time.

(06-26-2018 )snailexpress Wrote:  I will look blowby first. If truck was idling a lot it's about time to have cylinder polishing and carbon seized rings. Why oil pan gasket was changed?
How about overhead? How frequently regeneration is occurs?