CM2250 Poor fuel mileage

[Lonestar10]

Did you check the psv while doing leakdown test at 29k psi or regular idle?

[Truckdriven]

(03-05-2022 )Lonestar10 Wrote:  Did you check the psv while doing leakdown test at 29k psi or regular idle?

Checked it while doing leakdown test at 29k psi

[Rawze]

(03-04-2022 )Truckdriven Wrote:  ...
Also I ran Injector leak test and leakdown was 2090, 6k miles ago it was at 900, and 10k before it was at 340. I checked the rail relief valve and there was not a single drip. Something seems to be deteriating should I be concerned or wait till it gets worse and easier to find? fuel pump was rebuilt 17k ago.

The acceptable range is anything less than 4k psi on one minute (when doing the leak test at 30k psi) and its still ok.

[MCRENT]

Also I ran Injector leak test and leakdown was 2090, 6k miles ago it was at 900, and 10k before it was at 340. I checked the rail relief valve and there was not a single drip. Something seems to be deteriating should I be concerned or wait till it gets worse and easier to find? fuel pump was rebuilt 17k ago.
[/quote]

You might want to check the torque on the quill tubes. I had one that was leaking due to improper torgue. I was losing about 10K in a minute on the fuel rail leak down test and now she is sealed up and and holds above 29K for at least a couple minutes.

[Rockinbexpress]

Did you ever find a solution to your fuel milage problem? I have the same issue.

[Truckdriven]

(01-13-2023 )Rockinbexpress Wrote:  Did you ever find a solution to your fuel milage problem? I have the same issue.

No I really haven't, I am running this way thinking pulling a livestock pot in the PA hills never will be that great however most others running the same lanes are getting a full mpg better. I did adjust the turbo tables to get max boost to 35 but didn't change anything with economy and recently have been made aware that too high settings create excessive back pressure so maybe I should back it off some in the mid/light fueling but haven't had a chance to monitor or adjust it yet. I sometimes wonder if we have a carbon packing problem as was mentioned in this thread, https://rawze.com/forums/showthread.php?...4#pid74354
However I sure hate to just throw an overhaul at it and not gain ANYTHING from it but really wish there was a good way to know before I just tear it apart.

Questions I have for anybody, Does carbon packing happen on a demandated engine?? or only from the egr being fed into it?? if an engine is demandated and overhauled will carbon packing be permanently cured??? When did they start installing antipolishing rings from factory? could mine be built without them?? ESN 79502726

[Rawze]

There are a thousand + factors that contribute to fuel mileage problems.

If it were carbon packing causing it, then someone with experience could feel it when they turn the engine by hand.

An issue like that could be anything.. including the fact that maybe you have more average power or are driving it differently, etc. than other people.. and the truck and rear end specs make a huge difference too.

Could even be the head worn out and loosing compression.

Can also be a lot of non engine related factors .. even a bleeding Doser injector or fuel line somewhere dripping. .. or maybe even you filling the tanks to the very brim and it bleeds the fuel back out the bleeder-tubes as it warms up later. This is ion fact a big problem with drivers when they fuel. They try to put every drop of fuel into the tanks that they can.. and 10+ gallons sometimes.. bleeds back out as the truck sees its first hill, or as the fuel heats up and expands. -== NEVER EVER TOP IT OFF!.

When you fuel the truck... shove that pump nozzle as deep into the tank as you can.... when it 'Clicks' off on its own ... .. DON'T RE-START IT. -= IT IS DONE!. Adding more fuel is only going to end up on the highway somewhere as that tank and fuel heats up.

I know that certain model pete's and KW's are notorious fort developing a fuel leak right in a cross-member on the return lines.. and then drip fuel right down onto the damn driveshaft itself. -=-= Takes an expert eye to even see this, as there is almost zero evidence of this happening, and most truck owners will never find an issue like this on their own.. all wondering why their fuel mileage is total s#it.


HAVE YOU pressurized the fuel tanks with up to a max of 10-psi and let the truck sit for a few hours?.

-- You can pressurize the fuel tanks to 10 PSI by pinching off the bleeder tube on one fuel tank, and putting a bit of shop air on the other tank, to check for leaks or if air is getting into the fuel as a last resort.
WARNING::: - DO NOT ATTEMPT TO REMOVE THE FUEL FILL CAP WITH THE FUEL TANKS PRESSURIZED!, not even if there is only a few psi!.. That cap can hurt a person badly or break bones if it blows off there with only 10 psi of pressure on its backside!.


Pressurizing the whole engine will find a lot of fuel mileage issues.. and checking the head for compression losses.. and there are a whole host of things that can be checked.

Does the fuel mileage in the ECM match, fairly closely to what you can calculate to the pump on a receipt?. -=-- I.E.> does the ecm know where the extra fuel is going and is accounting for it?.

[Truckdriven]

The ecm is consistently showing .1 - .2 better than calculating by the tank.

[Mudflap77]

(03-02-2022 )Rawze Wrote:  

(03-01-2022 )stevegrutz Wrote:  I ran into a truck that was tuned by rr. It was getting horrible fuel mileage, still drove fine but had a hunting kind of rough hi idle. After various tests and data logging i realized the turbo speed rpm was 0 while running. Found a broken wire for the turbo speed sensor, and now the truck is running great again. It was also a cm2250 and it threw 0 fault codes for the problem.

yeah,... for some dumb damn reason, a lot of programs from the factory have what is known as a "virtual sensor" switched on for the turbo speed sensor. I can only assume it is used as a backup to the real turbo speed sensor if it fails. - I personally do not know why they would do something so stupid, as it makes the ecm often not throw faults, but instead try to guess at the turbo speed whenever the real sensor starts failing. this often leads to no fault codes at all sometimes when it does so, but an engine running like crap.

What kind of symptoms would you expect to see if the ecm was relying on a virtual turbo speed while going down the road? Random over boost while pulling ie. 40psi then next shift 30 to 35 psi?
Also mine regularly want to go into scr warmup. Coming off the road and parking at idle within 30 to 60 seconds you'll hear the engine change fuel consumption will go from 1.7-2.3 liters per hour to 7.5_8.5 l/hr insite shows its operating in scr warmup. If idled up to 900rpm consumption drops to around 4 l/hr and goes out of scr warmup.
If just left at idle it remains in warmup for a few minutes sometimes up to 10 minutes or so. Then return to normal and you can hear t change. Now if you were to set high idle or just rev it up and go back to low idle it will go back to scr warmup.
DOC/DPF replaced along with related sensor and emissions harness a little over a year ago.
SCR and temp and nox sensors was replaced shortly after, thinking DPF issues caused damage or plugging in SCR and temp sensors were causing this scr warmup issue and that did solve it. Any ideas? Engine is a 2350 485 if that makes a difference.