Fuel mileage still sucks

[Lead_sled]

(10-28-2021 )Redland1 Wrote:  Sand boxes?

Yes, sand boxes.


Just filled up. 482 miles, 105.7 gallons. 4.56 mpg

Here’s a quick video clip of my driving habits. I’m open to criticism. Just something recorded a few minutes ago. I’m loaded at 78k

https://youtu.be/BK1Ell-Lp58

[SquareOne]

Do you have a boost or pyro gauge? It would be nice to know what the boost psi is under load and while maintaining speed.
With 78k, sounds like you're pushing it pretty hard getting to get to speed. The rpm you're running it up to is a good habit to have though.

The norm around here for guys trying to get the best mpg is to keep the boost at 10lb and lower whenever possible. The pyro will typically tell the story as well. The more fuel, the more heat you'll create. The less the heat the easier you're being on the truck which should translate to better MPG.

When was the last time the doser injector was checked/changed?

[Lead_sled]

I do have a boost gauge, but no pyro gauge. I’m at 8-10 psi at 78k maintaining 67mph. When shifting through as you saw on the video, I’m able to keep the boost pressure at 25 psi and below unless pulling a hill while loaded. I’ve read a lot about the suggested driving habits.

[Lead_sled]

Not sure on the doser injector. At this point, not interested in doing anything with it since I’m about to de-mandate that business

[schISM]

One thing that jumped out at me while reading your posts was the dealer turning it up to 525. I’d have to research this but I don’t think any cpl.#’s are able to crossover the 500hp threshold. Either you have a 400-500 or a 525-605hp. I’d put it back to the original calibration listed on your ecm and see if that doesn’t help.

[Rawze]

(10-29-2021 )schISM Wrote:  One thing that jumped out at me while reading your posts was the dealer turning it up to 525. I’d have to research this but I don’t think any cpl.#’s are able to crossover the 500hp threshold. Either you have a 400-500 or a 525-605hp. I’d put it back to the original calibration listed on your ecm and see if that doesn’t help.

I agree.. I was about to post about the same thing .. lol.

What is the engine ser#? .. and what program exactly was shoved into it?. This could have been a bigger mistake that you think. Those stealers#its are clueless!.

[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.

=========

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".

[Lead_sled]

I’ve had the truck since March of this year. Was purchased from an uncle who dropped off at the dealership for any and everything.

I’ll answer as much as I can right now, but will take all listed suggestions and go through one by one as I try to find the issue. I’ve hauled these sand boxes and dry vans only. The fuel mileage when I first started doing it was 6-6.5 mpg. So, in the process of these few months, something has changed. The computer has always been a little off as they never 100% accurate, but even the computer used to reflect a similar 6-6.5mpg.

- I’ll check the doser as suggested with disconnecting and checking.
- Yes, I’ve done the EGR tune up thoroughly according to your posted videos twice with new sensors each time.
- I haven’t had the valves adjusted/set since I’ve had it. I would assume the Kenworth dealership did it last.
- I have not done an injector leak down test yet
- I would also assume the EGR valve is the original as it is the green one. Haven’t touched this one yet.
- The pressure test held, so I’m guessing the pipe that runs around the backside of the engine is still in tact, because no leaks.

Engine serial number. 79343994

It’s listed on the valve cover as 425hp

As far as insite, I’ll have to bring my computer back with me next trip. I’ll drive for another 2 weeks, then will take 2 weeks off. So, this will be a pending action item to see what all is shown there.

[GhostHauling]

So my two cents is. That truck is capable of easily 7mpg but pulling sand boxes as I’ve been there done that in Wv/Pa/Oh short runs + lease roads but up here allot of mountains my trucks would always be averaging 4.0 to 5.5 which is normal on trucks with 550 & 600 hp with 4.11 rears & 18 speed transmissions in these hills off road oilfield work but down there I couldn’t imagine it would be that bad but still don’t think you’d be getting the best. I’d ask some of the other sand haulers you run with in similar trucks what mileage there getting and know exactly what the best mileage is for what your doing. And lastly fuel mileage can be a big indicator of serious issues with your truck but sometimes you’d lose power as well I don’t know your situation but I’m guessing by the work your doing coupled by hauling ass which at least up here is the only way to make money pulling boxes in the oilfield is the cause and going super slow In that line of work probably won’t raise your mileage enough to cover the loads lost. When I got my truck I specifically said I won’t take it in the oilfield unless it starts paying the 14k a week it used to because the wear on the trucks is significant which is why I pull a flatbed and leave the oilfield to the trucks Specd for it.