Fuel mileage still sucks

[Rawze]

(10-28-2021 )Lead_sled Wrote:  ...
When I disconnected the exhaust pipe to put the rubber plug to pressure test, I didn’t see anything abnormal that would indicate the doser leaking.

...

- The only way to check the Doser for seepage is to disconnect the doser pipe from the turbo, push it back a ways so that you can see the injector tip for it .. and the go crank the truck up and see if its getting damp with the engine running.

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Also, has the thing had a thourough EGR tune-up?.. with all new sensors lkike the IMAP, exhaust back-pressure sensor?, and ensured that the back-pressure sensor circuit thru the thermostat housing is not plugged up?.

* How is the overhead valve adjustment set?.. Who did it?... as this is sometimes a big issue, as some mechanics do not set the injector rockers properly on the ISX's... and they suffer fuel mileage and other issues.

* Anyone bothered to do an injector leak test on it>?.

* If the dash is showing 4 mog .. and the fuel mileage is also 4 mpg .. and your actually driving it gently and slow .. then the ecm itself knows that the fuel is being wasted too... but NO.. it will not throw any kind of a high fuel consumption code.. it is not nearly that smart. Nor will it throw any codes for incorerectly reading sensors unless it is an extreme.. this is why doing regular EGR tune-up work is so important on these engines.

* Also, take a screen shot or 2 of the REGEN history (via cummins insite) on it.. what are the numbers on the for right of the screen?... this is also telling for how healthy the system is.

* Also, how old is the EGR valve?... it can stick open and the ecm will never know it, and fuel mileage will go to the dogs that way too.

* Was there any leaks in the EGR piping or boots that wrap around the back of the engine?.. Those 871's are bad about one of the rubber boots at the back of the head in the EGR piping going bad / rotting out and leaking, causing bad fuel milage.

* ALSO ... Anyone bother to clean out the crossover pipes and little block that the EGR Delta-P sensor is mounted to?... and replaced the Delta-P sensor?.. this is more EGR tune-up stuffs.

=== Like i said.. the list can be a mile long for simply "poor fuel economy".