(05-05-2018 )Trucker750 Wrote:  I have a 2012 cascadia with a cummins 11.9 400 hp it has 620k on it. The dpf filter was cleaned and mpg seemed fine, but then 250 miles down the road the outlet NOx sensor went out and was about 1500 miles of reduced mpg. From 6.2 to 5.8 mpg. The sensor was replaced, but instead of mileage going back up, it went down even more to 5.2. I'm losing 1 mpg now and dont know why... no codes, so I need someone who might know what's happened???

(05-05-2018 )hhow55 Wrote:  When they cleaned the DPF , did they do a maintenance reset?

(05-05-2018 )imalumberjack Wrote:  

(05-05-2018 )Trucker750 Wrote:  I have a 2012 cascadia with a cummins 11.9 400 hp it has 620k on it. The dpf filter was cleaned and mpg seemed fine, but then 250 miles down the road the outlet NOx sensor went out and was about 1500 miles of reduced mpg. From 6.2 to 5.8 mpg. The sensor was replaced, but instead of mileage going back up, it went down even more to 5.2. I'm losing 1 mpg now and dont know why... no codes, so I need someone who might know what's happened???

Could be totally off base but just want to bring it to your attention, have you up dated the fuel pump plungers? I have a 13' Pete with 11.9 @425 and it ate the plungers and caused fairly severe engine damage .... only has 205,000 miles

(05-08-2018 )Rawze Wrote:  There are a lot of causes for fuel mileage dropping. Simply cleaning the DPF properly is not one of them. Something else caused it. Perhaps they worked on something else or replaced a sensor with a defective one?. Maybe a leaky doser injector?

(05-08-2018 )Trucker750 Wrote:  

(05-08-2018 )Rawze Wrote:  There are a lot of causes for fuel mileage dropping. Simply cleaning the DPF properly is not one of them. Something else caused it. Perhaps they worked on something else or replaced a sensor with a defective one?. Maybe a leaky doser injector?

They swear up and down they didnt touch anything else except the dpf filter. I know it has been a fleet truck belonging to them since new, and while they have always kept good maintained I'm pretty sure they have never cleaned any of the egr or intake system. I'm planning to clean it all, but I dont want to until I'm sure that is the sole cause of the mileage loss. Is it possible that a clogged intake system could account for the instant drop of 1 mpg just because the dpf was cleaned? Maybe the egr valve is so clogged it can't open normally, and the change is exhaust backpressure is now requiring more or less flow that the clogs will allow, equaling lost mpg? All without throwing codes? I'm a mechanic as well as a driver, but the computer systems nowadays are new to me.

(05-08-2018 )Trucker750 Wrote:  

(05-08-2018 )Trucker750 Wrote:  

(05-08-2018 )Rawze Wrote:  There are a lot of causes for fuel mileage dropping. Simply cleaning the DPF properly is not one of them. Something else caused it. Perhaps they worked on something else or replaced a sensor with a defective one?. Maybe a leaky doser injector?

They swear up and down they didnt touch anything else except the dpf filter. I know it has been a fleet truck belonging to them since new, and while they have always kept good maintained I'm pretty sure they have never cleaned any of the egr or intake system. I'm planning to clean it all, but I dont want to until I'm sure that is the sole cause of the mileage loss. Is it possible that a clogged intake system could account for the instant drop of 1 mpg just because the dpf was cleaned? Maybe the egr valve is so clogged it can't open normally, and the change is exhaust backpressure is now requiring more or less flow that the clogs will allow, equaling lost mpg? All without throwing codes? I'm a mechanic as well as a driver, but the computer systems nowadays are new to me.

Also, would a leaking dose injector be found by doing a leakdown test on fuel pressure, and also would it be zeroed in on by elevated temperatures in the def system sensors? I'd like to know if I can say positively its leaking by simply using insite software.