Isb scr conversion efficiency nightmare

[dslmchnc]

I've got 2 isb Cummins in freightliners that have the same conversion efficiency and regent quaility codes. During the scr test the catalyst is the only thing that fails. We replaced one and it still has the same issue. I believe the inlet nix sensor is causing our issues. What should I be seeing for ppm during a Regen? And the inlet should be higher than the outlet correct?
Thanks

[Rawze]

NOx sensors, as they get some age on them, tend to read incorrectly, never throwing a fault.

Could also be bad DEF fluid or clogged DEF nozzle?.

[dslmchnc]

(10-12-2018 )Rawze Wrote:  NOx sensors, as they get some age on them, tend to read incorrectly, never throwing a fault.

Could also be bad DEF fluid or clogged DEF nozzle?.

Def has been sampled and tested with our refractometer. Def dosing injector has been flow tested and cleaned. The inlet nox is consistently reading higher than the outlet during the scr performance test. Should I suspect the inlet nox sensor? We replaced the outlet when the scr was cleaned.
Thanks

[Rawze]

check to ensure the program matches the engine ser#. You may be chasing a ghost. Maybe Uni or one of the guys who works on those more than I do have some ideas too?.

Maybe the engine making too much NOx?.

[Signature620]

Inlet NOx will always be higher than outlet NOx - That's what the catalyst does.

[Hedley]

This may sound a little far fetched but check the wire harness going from the SCR to the DEF tank especially where the harness bends around brackets, the wires tend to rub through the insulation due to vibration where the wires contact the loom sending false readings.

[Unilevers]

whats the ppm during a regen in and out?