rookie mpg question

Same suggestion, but I'd take it to Central Power across from the yard, and have them do the overhead and pressure test the charge air cooling system as a first step. You couldn't get me to let "the shop guys" touch my engine. Prime has a deal with Central to get it done cheaply.

You can also have them check your software for the latest version as well.

 

Get the overhead done for sure and how many miles ago did you change your fuel filter? OnGuard and stability control have nothing to do with mpg or deregulating the motor. The only OnGuard will do is turn the engine breaks on if you start getting to close to something and that would need obvious in both sound and shifting.

Also, listen to IP, he's very knowledgeable.

 

Sometimes... don't use that sentence in the presence of my ex's!

 

I change the fuel filter every 25k.

OnGuard derates the motor as the first stage of slowing the truck as does the stability and traction controll. It derates the motor before it uses the engine break or service breaks. Stands to reson it could derate the motor if there was a malfunction in the system somewhere no?
RTFM.

I've been stuck with this problem for years and it's getting old, not the first truck with this problem. air/fuel filters, overhead, CAC tests ok, been to Freightliner shops only to be told they can't find anything wrong. It dosn't throw and codes so they don't know what to do, lol.

How could there be nothing wrong with a truck that needs to be downshifted when mty on a 6%, or down to 7th gear half loaded on a 4%. Prime does limit the rpm which has an indirect affect on the power but that's as far as it goes. They don't turn them down to the point of pulling a grade @23mph, the trucks are doing that because something is wrong and it's widespread problem.

Yes IP is knowledgeable and has good advice.


Freightliner can't find a problem, all the usual is ineffective, it's isnt specific to Detriot, and it's intermittent slowly progressing worse. What does that leave? What does a "Prime" Pete and FL have in common? The collision avoidance is different manufactures? What is left?

 

It's the biggest complaint I hear from other drivers are the gutless trucks. The engines aren't speced for the max hp/tq but they have enough you won't be the slowest one up a hill when they are running right. You should be able to take it easy on the throttle and still pull a grade with no problem and get good fuel mileage. You shouldn't be spending the whole day trying to recover from a steep grade or two.

Shift at low rpm, progressive shift, run @1260 rpm just to hover close +- to the minimum mpg requirement? That isn't normal! Yes there are more variables involved but not enough to warrant such difficulty.

Sometimes the fuel mileage is better running faster, not because of a CAC leak, but because the roller coaster won't finish the track if you slow it down. Derated motors don't have the power to be efficient!

Iv'e been through this before and all the basics of getting good fuel mileage and engine maintenance are just dirty band-aids to a bigger problem. Spend some time in a truck that is running proper and it's a night and day difference.

 

You have to learn to "float"
I have a wind map shortcut on my screen I can check wind direction and speed so to adjust accordingly.

Let her come up gentle on the gas, downhill easy on too, from complete stop to freeway speed take your time, install a scan gauge if your truck has no way to show you throttle input.

 

Skellr. I think what you're hitting is the turbo boost limit programmed into the ECM. The turbo on a DD15 can put out 40 psi, but its been limited to 20 or so to keep the rookies under control. I've got an older truck, and under certain conditions I can get around the limits. What an unchained DD15 can do is impressive. It'll also empty your fuel tanks in a hurry.

 

I understand what you are talking about but thats not it.

There is definately some intermittent problem that gets worse over time. It happens more and more frequently untill it's always messed up. I still have a bit more driving to do today.

 

They assigned me a 2015 international. As soon as it started getting cold, my truck just crawls up grades now where as it would accelerate up them before. Maybe it's the winter blend?

 

Forcing your way through cold, dense air has more of an effect, but yep, the lower cetane rating of winter blend doesn't help a bit either. Or the wind and storms. Or that diesel engines loose efficiency when they are at colder operating temperatures. Bet you're not as aggressive about checking your tire inflation on cold mornings too...