New Paccar DEF and boosting concerns...

Turn it in get a new one. Problem out of the gate.more to follow

 

DEF won't affect engine performance because it is injected into the exhaust stream typically several feet after leaving the turbo, into the SCR system. The only time it would interact with the engine is if it senses an error that should show a code/light, which will then lead to a derate. I have a DD-15 so can't tell you specifics on your engine but it should be about the same. EPA/CARB regulations mandate these "protections" to the environment, not DOT/FMSCA. So first it will derate your power about 15-25% and you will definitely notice that. If you don't get it fixed then within some timeframe that depends on usage it will limit you to 55mph. Ignore that and it will eventually limit you to 5mph, but usually (not always) that will happen when you stop and set the brakes, the system "assuming" you are in a safe place to be parked.

If you dropped two injectors already there is certainly something wrong inside.

 

Aftertreatment and engine are 2 different systems but they work together. Many times people focus on the aftertreatment system when it acts up. What's upstream of the aftertreatment system? The engine. Any issues on the engine side can easily have an effect on the aftertreatment system. Just saying to look at the whole picture, not just the SCR system.

 

For comparison sake my 2015 isx cm2350 uses 4% def to diesel. Measured it several times and this is accurate.
Unless the mx has its own emissions system now, I thought they were using cummins dpf and def systems.

There is definitely something wrong internally, aside from the def usage. Separate issues would be my guess. Unless it's some kind of electrical issue. The bad thing about these new engines is if it thinks a sensor is bad it will prevent it from continuing on, putting you on the side of the road in the process.

 

I would be more concerned with getting 5mpg unless you just run West Virginia grades all the time...

The DEF usage sounds alarming, but each manufacturer may have different ways to reach emission requirements, might be higher usage during break in for whatever reason, but should definitely get it looked at regardless.

Boost pressure has a computer controlled wastegate so unless they program it to let off for whatever reason, you should be getting consistent pressure if the pedal asks for it.
Maybe has something to do with EGT's, but then why spike up higher then before?

All of these things combined sounds like a recipe for potential disaster down the road if not checked out, or at least saddling you with way higher running costs in the mean time.

The only thing for sure is, from the various new trucks I have driven, none of those sound like 'normal' behavior at least from a Freightliner/Detroit perspective

 

@daf105paccar

 

DEF usage also depends upon fuel consumption.
I do about 2,000 miles a week. I use about 15 gal def per week in summer and over 20 gal def per week in winter.

 

What gross weight do you run at?
What % off empty miles?
When do you upshift or downshift?(rpm)

DEF usage is linked to MPG.
The lower MPG the higher the DEF usage.
DEF usage has no influence on the engine performance.