CM871 fuel mileage

[JimT]

I got a 2012 pete 587, 3.36 rears, 13 speed, mid roof pulling a 48 flat. At it's worst (not including the extra bad DPF death spiral time of nearly non-stop regens) I was getting 6's for mpg running 70ish all the while lugging the engine between 1350-1450 rpm. Back then (before I learned better, seriously, it's what I had been taught) I ran 1100 to 1500 rpm. Basically never went over 1500, though she complained under heavy loads under 1200 rpm. Back then setting the cruise at 1350 and 1450 rpm would produce then best fuel mileage, even up to the 8's at times.

NOW I know better. Once I'm out of the lower gears I keep it between 1550 and 1800 rpm. Rarely ever shift into top gear anymore as 68 mph is only 1450 rpm and I only run it there when empty on flat land with the boost 10psi or less. These days I rarely use more than 20-22 psi to climb hills. If my climbing speed drops below about 45 mph then the lower (10-15 psi) boost levels don't result in any better mpg's compared to climbing at 20-22psi while maintaining 45mph or higher. I'll "cruise" down the road with "foot control" engaged, anywhere from 55 to 64 depending on load and terrain, taking full advantage of gravity assists often rolling down hill with transmission in neutral.

It took me a while to get used to running at higher rpms and the different sound of the engine above 1500. But, after my inframe it sounded better and now that the rings have set it's really smooth and finally seeing fill-ups in the mid 8's again. Some of my worst fuel mileage these days is hauling lightweight roofing insulation (ISO). Tall and light with flapping plastic on the top, those loads average mid to low 7's (while loaded) from PA to New England mostly along the 84 corridor. Sometimes my ISO loads even drop down into the high 6's when there's high winds like we saw in March. Lots of additional factors when flatbedding.

[superbudy208]

I've tried driving it several different ways, by the foot different speeds cruise no cruise it don't matter at the moment, I just went 1000 miles half loaded and half very light and averaged 5 mpg's and found the truck will not move unless it has 20 psi of boost, I did notice on a long seeping right turn the other night the truck freed way up gained speed and had to let of the pedal, this week I'm going to get the alignment done and see if the chassis is binding up

[superbudy208]

also found my boost gauge flutters alot under hard boost but will go to 37-38 psi

[Waterloo]

When was the last time the cans removed, baked and de-ashed? And the transmission, it is in need of some serious reprogramming.

[superbudy208]

I'm not sure when they were cleaned last they were all replaced with in the last 300k miles. I seen the receipts for them when I bought the truck, and yes dos need some programing also it wont run past 1750 rpms and in 9th gear it will lose power until 1500 rpms, i had peterbilt check it out and they said it was all up to date

[superbudy208]

Also looking for someone good with the programming

[Waterloo]

From some of the symptoms, those cans are in need of cleaning or replacement. More than likely replacement. The fluttering turbo and you not having any power, I bet both the DOC and DPF filters are shot. You need to drop the cans, post photos of the face of both cans.

As far as programming, you need to find someone with the Eaton transmission software the can change the shift points in the transmission, someone that actually know what they are doing. You are just destroying the motor the way it is set up to lug and more or less tear the liners out of their seats.

I would fix the shift issue and drop those cans to inspect. You are simply destroying this motor every day you drive it. I am surprised you have not lost a liner yet. And I hope they cut the ledges in the block when they last in framed it...

Me, get the truck to Georgia, let Mr Hagg fix it once and for all, because at the rate you are going it will be in need of another in frame in a week or two.

[superbudy208]

I think a lot of the problem is with the gearing of the truck, @ 75mph it's at 1550rpms in 10th, @ 70 its running 1350 to 1400rpms, and 9th at 58mph is 1600rpms,if I go slower in 10th it lugs it it to much, it does have power its not low well I don't think so anyways, the turbo fluttering almost seems like it popping back through the intake under hard load load sometimes its worse than others, I'm going to run the overhead again and make sure it was done right, I do want to drop the cans but it'll be a week or 2 before I get a chance to.

I've been trying to shift it higher and but it has a problem running in 9th it goes to 1700 and won't go higher then after 15 seconds it slows down to 1500 and you cant push it back over 1600 rpms, I'm going to check with the dealer and see if they can adjust it, I've talked to a few people about programming it, but not really sure I want to go that way.

Also I've called Hagg several times but they never call me back so

I don't really want to do an in-frame on it, that's why I keeps the rpms up but its killing me on fuel and need's the front structure done soon to. Also looking for some 3.55 or 3.73 gears and waiting to hear on a Volvo with a 13 speed that has bad cams trying to figure out which way to go still

[Waterloo]

(06-04-2021 )superbudy208 Wrote:  I think a lot of the problem is with the gearing of the truck, @ 75mph it's at 1550rpms in 10th, @ 70 its running 1350 to 1400rpms, and 9th at 58mph is 1600rpms,if I go slower in 10th it lugs it it to much, it does have power its not low well I don't think so anyways, the turbo fluttering almost seems like it popping back through the intake under hard load load sometimes its worse than others, I'm going to run the overhead again and make sure it was done right, I do want to drop the cans but it'll be a week or 2 before I get a chance to.

I've been trying to shift it higher and but it has a problem running in 9th it goes to 1700 and won't go higher then after 15 seconds it slows down to 1500 and you cant push it back over 1600 rpms, I'm going to check with the dealer and see if they can adjust it, I've talked to a few people about programming it, but not really sure I want to go that way.

Also I've called Hagg several times but they never call me back so

I don't really want to do an in-frame on it, that's why I keeps the rpms up but its killing me on fuel and need's the front structure done soon to. Also looking for some 3.55 or 3.73 gears and waiting to hear on a Volvo with a 13 speed that has bad cams trying to figure out which way to go still

Make an appointment with Mr Hagg... They are one of the only shops, and a very small shop, in the entire USA that can consistently repair and rebuild an ISX, they do not have time to call you back. Make an appointment and stick to it. Until then, you are just spinning your wheels and throwing money out the window while pissing the rest away. You have too many things going on with this truck to simply say go get an Inline reader and do this. You have multiple issues, all from abuse of not properly maintaining and or understanding the proper operation of an ISX. If you cannot get to Mr Hagg, your best bet is to off load that truck. The one with the bad cams... Are you serious?