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Rawze · 02-28-2022, **(Subject: CM2250 Poor fuel mileage )**

the IMAP and exhaust pressure sensors can cog up even if it is de-mandated. maybe start by doing some sensor replacements and ensure the feed circuit thru the thermostat housing for the exhaust bp sensor is not plugged up.

as far as walnut blasting.. here is some older discussions on it...
ref: http://rawze.com/forums/showthread.php?t...3#pid10573

Truckdriven · 03-01-2022, **(Subject: CM2250 Poor fuel mileage )**

(02-28-2022 )Rawze Wrote: the IMAP and exhaust pressure sensors can cog up even if it is de-mandated. maybe start by doing some sensor replacements and ensure the feed circuit thru the thermostat housing for the exhaust bp sensor is not plugged up.

Sensors were all replaced along with t-stat housing cleaned

(02-28-2022 )Rawze Wrote: as far as walnut blasting.. here is some older discussions on it...
ref: http://rawze.com/forums/showthread.php?t...3#pid10573

So according to that I will pull things apart and see how bad it is, the truck had EGR up until I bought it and I have no idea if it ever had any egr maintenance.

Lonestar10 · 03-01-2022, **(Subject: CM2250 Poor fuel mileage )**

My oem turbo failed would work fine between 0 and 28% then would not go any further and never threw a code. Vgt ring was getting stuck

Truckdriven · 03-01-2022, **(Subject: CM2250 Poor fuel mileage )**

(03-01-2022 )Lonestar10 Wrote: My oem turbo failed would work fine between 0 and 28% then would not go any further and never threw a code. Vgt ring was getting stuck

How did you diagnose or find this??

Lonestar10 · 03-01-2022, **(Subject: CM2250 Poor fuel mileage )**

Watching the vgt commanded and vgt actual in CT also when vgt controller was removed the arm on turbo would not move far

stevegrutz · 03-01-2022, **(Subject: CM2250 Poor fuel mileage )**

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.

Truckdriven · 03-02-2022, **(Subject: CM2250 Poor fuel mileage )**

(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.

Interesting..... Just tonight I was at the back of the trailer when he started it and after maybe 30 seconds or a minute it started doing the hunting thing at idle, it was subtle and probably would be missed by many people but was immediately obvious to me. I had caught it doing it once before but when I asked the regular driver he didn't know anything and I thought next I was just confusing it with another truck, now I know it did it, but it only does it occasionally. Gives Me one more thing to investigate.

Rawze · 03-02-2022, **(Subject: CM2250 Poor fuel mileage )**

(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.

Truckdriven · 03-04-2022, **(Subject: CM2250 Poor fuel mileage )**

(03-02-2022 )Rawze Wrote: 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.

I was watching turbo speed with Insite and unplugged speed sensor , reading went to 0. Ran for 3 minutes till I shut it off and it But never threw a fault code. Does this indicate "virtual sensor" is turned on in the program?

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.