CM2250 Poor fuel mileage

[Rawze]

(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.