Horrible mpg
04-01-2020, (Subject: Horrible mpg ) 
Post: #1
Horrible mpg
isx 2250 motor is approaching 600k miles and it has never seen 7 or better despite having new imap , exhaust back sensors and egr temp sensor replaced still averaging 5.9 or 6.2 I'm typically north east at 62mph and don't ever use cruise control...any suggestions?
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04-01-2020, (Subject: Horrible mpg ) 
Post: #2
RE: Horrible mpg
Go to quickserve.cummins.com and under symptom search you will find "Fuel Consumption Excessive". Also, have you completed a complete egr tuneup, which is more than just replacing sensor's.


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04-01-2020, (Subject: Horrible mpg ) 
Post: #3
RE: Horrible mpg
What is the gear ratio?
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04-01-2020, (Subject: Horrible mpg ) 
Post: #4
RE: Horrible mpg
Replacing sensors isn't going to dramatically improve your fuel economy. Make sure the EGR circuits are cleaned out, check for boost leaks & check for recent fault codes.
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04-02-2020, (Subject: Horrible mpg ) 
Post: #5
RE: Horrible mpg
Fuel mileage issues can be 1,000 things. Everything from CAC leaks, egr or emissions system issues, leaking doser injector, fuel rail pressure or injector issues, APU leaking fuel when running, return line leaking onto exhaust or some place where it is not seen, etc...

then there are various reasons why it may not be as high as expected based on driving habits, gear ratios, problems with the truck itself or how it is spec'd, loads, type of freight and/or terrain/conditions,...etc.


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04-02-2020, (Subject: Horrible mpg ) 
Post: #6
RE: Horrible mpg
As someone who lives in the NE, I'll add that traveling in the NE can actually be worse for your fuel economy. Once I get east of I-81 and North of I-80 I consistently see a drop in fuel mileage, regardless of load, even with an empty flatbed. The terrain and traffic does not lend itself to optimal driving techniques. Running I-84 from Scranton, PA to the MA line (a regular route for me) always results in lower fuel mileage. That being said, my 2250 can still manage 7 on an average day in this area, BUT that depends entirely on location. When I run a load out of Northwestern CT down to NYC I may only get 5.5-6.5 mpg between the hills and stop and go traffic.

Suggestions, try dropping your speed. If you have a boost gauge try to keep it 5-15psi, even on climbs. I've found I can climb most grades at a maximum of 22psi boost to maintain speeds 45-55, while 15-18psi when I drop lower. Most of the time I keep the boost between 5-10psi, operating between 1400-1600. (1500-1700 for most grades at higher boost levels). Sometimes I let it get down to 1300 before I downshift, but only when I'm running 10psi of boost and usually it's only because I'm about to crest the hill or I screwed up and wasn't paying close enough attention.

When running purely by boost you will spend part of your time driving 45mph or so up the hills, but the flip side is, with enough weight, you'll easily be able to hit 80 on the way down. The average travel speed once all is said and done for me is usually right there between 58-62mph.

I WAS getting about the same numbers you mentioned while my aftertreatment was still intact, however I was active regening, on average, 50% of each day! After the surgery I gained about 1-1.5mpg which was all getting dumped in to the exhaust.

Just for reference: I have a 2012 Pete 587, cm2250, 13 speed, 3.42 rears. Top gear is 1400 rpm at 65 mph and 1500 rpm at 72 mph. I have a mid-roof and run flatbed. Tall and light loads are worse for my fuel economy then short heavy loads. I also have a significant amount of blow-by and am currently using about 2-2.5 gallons of oil between about 10k oil changes. Just hit 550,000 miles.


What else can you tell us about your truck, trailer and operation? What kind of maintenance history? Do you have Insite? Any current problems, MIL's or CEL's? How's your oil consumption, oil change intervals, aerodynamics, tire wear? What parts of the NE do you frequent? Slowing down, limiting boost is probably the biggest thing that will help, but as Rawze said there are 1,000's of variables.


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 Thanks given by: Rawze , Pd6cas2
04-02-2020, (Subject: Horrible mpg ) 
Post: #7
RE: Horrible mpg
(04-01-2020 )Volvo8873 Wrote:  What is the gear ratio?
thanks guys and Rawze!! For the reply ...3:55 gears matted to a 13speed with 295/75 /22.5 tires ... it has no power loss even when loaded heavy that's why I'm confused? codes or check engine light. But like rawze stated it can range from a variety of reasons and I will start by checking CAC leaks
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04-02-2020, (Subject: Horrible mpg ) 
Post: #8
RE: Horrible mpg
Wish I had your gears, then I could spend a little more time in top gear.

It took me a lot of testing to fine 1400-1600 to be my best economy range. Actually, 1350 rpm in top gear (63mph) on cruise used to give me 8-8.5mpg all the time. BUT that was before I learned that below 1400 wasn't good for the liners at higher loads. When I first got the truck I learned pretty early that anything below 1250-1300 under a load just didn't feel right from the engine. But now that I know better I try to keep the rpm's higher and the boost lower. Took a fair bit of work and tweaking to get higher mpg with the higher rpms and lower boost. I didn't mention it before, but I know my CAC has a leak near one of the mounting points. The thing is, when running with the least amount of boost possible you don't notice the loss like you would when trying to make higher boost. At least that's what the numbers look like to me. Like running I-84 east bound through NY just past the Newburg-Beacon bridge. I can climb that grade by the Stormville rest area with 15 psi boost, I just end up moving about 25-30mph for a minute or two.

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Do you have Insite? What does your regen history look like? You could be losing some of your fuel mileage to more frequent regens or regens that are struggling to complete properly. When was the last time you did a full EGR tuneup? (not just replacing sensors)


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