CM2250 Poor fuel mileage

[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.