Cummins ISX CM871 Regen Temps Question

Could be a bad temp sensor as well. Or needs to be re-calibrated.
FAULT CODE 1691
Catalyst Efficiency - Out of Calibration
The electronic control module (ECM) detects that the temperature differential across the
aftertreatment diesel oxidation catalyst during active regeneration is not matching the
expected temperature increase.

 

Take it to a Cummins dealer and have them check. Keyword is Cummins dealer. I had regen issues on my 13. There was a ECM update that fixed this issue on mine.

 

Bad temp sensor

 

The temps you have listed probably will never cause a fault. I see those temps all the time on successful regens. Most regen faults get logged after a failed regen, when the engine and everything else is right up to operating temp and has been there for hours. It is quite common for us to follow the TS and perform a regen and everything is fine because we started with an engine that hasn't been running for hours and has cooled down. You would have to try a regen with the truck freshly back from a long run and see what happens. I have had several regens fail with a fully hot engine and exhaust systems. Once the truck has sat for 8 hours and the regen retried it takes off and performs a perfect regen. The reason for this is not always the same. This is where you need to reproduce the situation that is causing the fault. I know it is easier said than done, sorry. Weak metering actuators and warped diffuser plate in the turbo are common problems that get worse with hot engines versus warm or cold engines. Cummins does have requirements to remove and clean the doser injectors because they do get plugged up rather easily. Also, is the DOC and DPF due for cleaning? It sounds like you have access to Insite. When running a regen you need to open up data monitor and watch all the exhaust temps and doser injector state. Once a regen is initiated the DOC inlet and DPF inlet need to reach about 525 -550 degrees. This is actually done by the turbo vanes closing, causing high exhaust back pressure and load on the engine. Once the system reaches 525 or better then the doser starts to inject fuel to get the really high temps. If the system doesn't reach this then something is wrong with engine, not the DOC or injector. If the temps reach 525 or better and the inlet temp to the DPF stalls around 800 or is very very slow to reach 1000+ then something is wrong with the injector or DOC. Monitor these parameters during a regen, and you should have these values;

EGR differential pressure - less than 0.5" Hg - if higher, could be stuck open/leaking EGR valve
EGR valve position - 0% - EGR valve must be closed.
Exhaust gas pressure - 120-150" Hg - Low could indicate a failing turbo.
Intake manifold pressure - 10-14" Hg - Low could indicate boost or air to air leaks.
Percent load - less than 2% (with the fan off) I've seen most regens fail with this at 5% or higher. This is also what is near 0% with a cold engine and 5-7% with a hot engine. Typically a weak metering actuator, the engine heat makes the actuator weak.
Turbo actuator position - 89% or higher 87% or less will cause a drop in exhaust temps, but there are no codes for this. Usually a failed turbo.
Turbocharger speed 40-45K rpm.

 

Was the DOC cleaned with the dpf too? If not, I would try that. The precious metal coating inside the DOC that makes the burn take place can get washed away over time too resulting in weak DOC performance.

 

Sounds like the DOC is on it's way out.