CM871 fuel mileage

[Rawze]

(05-09-2021 )superbudy208 Wrote:  ...I try to cruise around 68 to 70
...

If you slow down a bit... to 63~ish it would help tremendously.. and stop using the cruise control. - Learn to keep the door shut more and don;t stop once you pick the load up.. narrow down that window of driving speed vs. average speed. Ideally you want your driving speed to be within about 7 mph or so above the overall pick-up-to-delivery average based on the total miles.

I.E.> if a UPS, fedex, or other load averages 50 mph (50 mph is an industry standard for average delivery times LTL), calculated from pickup time to its delivery time, based on its total miles (most of them do) ... Then you should be able to drive it at ( +7 to +8 mph above this average) 57-58 mph down the highways to get it there. We do this a whole lot ... and we are very, very good at it. if you find yourself driving +12 mph or maybe even +14 mph faster then the total mileage average calls for.. then that is simply poor planning, poor driving habits, or some other issue of one sort or another that can be eliminated so that you can push for better fuel economy and higher profits.

(05-09-2021 )superbudy208 Wrote:  ...I try not to lug it...
1500 rpms and will down shift around 1200, I don't really go over 1500 very often
...

your absolutely torturing that engine... and it sounds like the Auto-S$itter is programmed horribly to limit power output by lugging the engine everywhere its whole life. - That engine was made to run between 1100 and 2100 rpm ... Anything below 1500 or under while heavy load is torturing it in the bottom 1/3 of its working range though, and beating the h$ell out of the liners and bottom end. The way you describe driving it is exactly how people torture an ISX and then wonder why they have big problems and a severely shortened life out of one. Not keeping it in the higher RPM ranges when heavy is how people loose liners and end up with problems out of an ISX. - and like you claim... if if does sound of "feel" like it does not want to run above 1500, it is because no one has run it there much ... which is horrible.

That engine will last much longer if you use those higher rpms, making less wear over time vs. high torque. It is higher torque and lower RPM that wears the ISX and other 15-litre engines the most. A person could get into your truck and drive it for the next several years at 1700 rpm everywhere it goes, drop[ping to lower gears to keep the rpm up when pulling, and the engine will last twice as long as someone always trying to keep rpm to a minimum, and below 1500, working it hard with high torque demand.

-- That thing, when pulling hard against a big hill or mountain, really anything more than about 40% on the fuel pedal ... should shifting be in the 1500 - 1850 rpm range... not down below 1500. - If it complains, like you said,... its because no one has driven it enough up there ... Replace the crank shaft damper if it is more than 5 years old, or has more than 500k miles on it... and BREAK IT IN UP THERE IF NEED BE ... and stop trying to torture that thing everywhere cuz it makes you "feel better" ... that engine will do it, as it is hard on it at high torque below 1500RPM!.

So... this means that you need to re-learn how to drive that thing much better... and YES it will save you fuel if you learn to drive it at higher RPM when pulling ans LESS BOOST! and better gear ratio .... instead of torturing it with a huge bunch of torque at low rpm. there are about 50 or so people a year that come on here, many learn this the hard way after an engine failure, fretted liner, or blown head gasket due to that kind of torture ... and heave to re-learn how to drive their tucks.

and oh yeah... DRIVING BY YOUR BOOST GAUGE by keeping it below 20-PSI or lower if you can.. and using higher RPM (1500 - 1900) and actual power with a lower gear range instead of higher torque and lugging it below 1500 when climbing a hill.

(05-09-2021 )superbudy208 Wrote:  ..
I've tried running 63, 64, and found the mileage was the worst its been

This generalized bulls$it of "I get worse fuel mileage by slowing down" is just that... something is wrong with how your driving it (too aggressively at lower speeds),.. possibly your lugging it terribly and creating a lot of inefficiency, and/or the engine itself needs to have some issues solved ... because slowing down and it consuming more fuel goes against the laws of psychics and thermodynamics. - Slowing down DOES NOT CONSUME MORE FUEL unless something is sucking it up improperly. Possibly...

A). Because you have horribly-spec'd rears for a 10-speed and driving a pete 387 in its Aero-sweet-spot of 63~-ish mph. Your geared wrong and doomed to lug the engine at 1300 or so with high torque if you drive it in top gear at 63~ish with a set of 3:36 rears. Those rears are terrible when considering a 10-speed is in front of them. No way to split the gear and fix it like you could do with a 13-speed.... even tho this still would not be optimal. BETTER SPEC REARS is the answer.

B). You have an Auto-Sthitter tranny which is going to take away roughly 0.6 mpg for every mile you drive, simply because a decent driver can out-shift that thing and save that much fuel all day long.

C). Depending on the health of your emissions and egr systems, if it often found that when its in bad shape and in dire need of an EGR-Tune-up .. the fuel mileage will go down when you slow down... (seeming against the laws of physics itself) ... simply because the engine is not breathing well and because sensors like the IMAP and exhaust pressure sensors are giving incorrect feedback. -- PERFORM an EGR TUNE-UP!..

This leads to the next couple questions ... Is this thing De-Mandated(deleted)./.. and if so, by who and what was done mechanically and who's programming is in it??

-- Sound to me so far, your journey towards owning that truck has just begun... I grantee you I could get a hold of that truck and get it into the 7+ mpg range If I drove it, worked on it, and took your freight. - It is a matter of knuckling down, solving all its issues, Having the discipline to SLOW THE H34ll DOWN A BIT to narrow the avg. speed vs the drive speed to less than 7 mph difference during the whole driving shift ... and making any changes to get me there like putting a set of 3:79's or 3.91's in it and re--programming that tranny to let her run up to 1850 like it should be, etc..

-- If I could do it ... so can someone else....

However, I would have never purchased a truck with horrible rears like that, especially with a 10-speed Auto-shitter in front of them. Whoever Spec'd that truck initially had their head up their arsse,. or was one of those fleets who could give a damn about the engine, was willing to lug and torture it to death in attempts to slow their company drivers down. - its like shooting yourself in the foot before the race and then wondering why your slow and dizzy half way down the track. Fleets are notoriously bad for spec'ing trucks like this these days.

I haul 80k Water loads for Nestle out of Pennsylvania across I-70 ... even in those big hills and 80k loaded... I still break 8.2 - 8.4 MPG. My engine never sees anything below about 1500 the whole time I am in those hills.

I haul loads of Wire from South-wire out of Kentucky that is in excess of 76-78k... down into Georgia across Mont-eagle mountain... AND I BREAK 9+ MPG CONSISTENTLY WITH THOSE LOADS.... so yeah...

So as far as I see it ... 5 mpg is horrendously bad for an aero truck, even with flat-bet freight and that 70 MPH every where you go does nothing but fund these guys personal islands!.



I Don't know about any one else.. but i think they are rich enough .. they don't need my money too... I think i'll learn how discipline myself to keep that money in my own pocket instead of wasted fuel.


- Drive it right.. Drive it by a boost gauge.. Use better discipline... keep the door shut and keep it moving so you can go slower and still make the delivery .. Fix its issues, Make changes for better fuel economy, etc.etc.etc... because the BIGGEST fuel mileage issue at the end of the day ultimately ... IS THAT NUT BEHIND THE WHEEL! (yourself).