scr warmup

[Mudflap77]

(05-10-2023 )JimT Wrote:  

(05-10-2023 )Mudflap77 Wrote:  I graphed the temps while test driving no sharp changes on the graph.
The temps I posted are just when I happened to look at the screen. as far as the temp differences I'm guess it would be the as when things are warming up DPF out let would be hotter then SCR temp. As exhust flow cools down DPF would read cooler then the SCR. My main focus was that there wasn't a large difference between the reading.
The only exhaust related temp that is calculated is Exhaust gas temperature(calculated) during SCR warmup it runs around 750F after it gets out of SCR warmup it settles at about 350F.
I haven't had those temp sensor unplugged since they were replaced about 10 months ago, if memory serves they can't be swapped.
Decomp tube was checked out a couple of weeks ago and no buildup, exhaust was checked no leaks, and Vee clamps removed for checking the Decomp were checked and retightened twice since being removed(i've had them settle before).
DPF and DOC were new 14 months ago. Regens are typically 100 to 110 hour apart, current Ash load is 29.4%. I will get a pick of regen history here shortly as requested by Rawze.
I get the point of the SCR warmup but if 260F is above the warmup threshold 400F should be right?
Thanks for the reply

Forgot to mention, check the functionality and accuracy of your outlet NOX sensor. I remember reading about some of them giving inaccurate readings when they go bad making the system think the NOX is too high but not out of bounds and constantly trying to compensate. It's possible the excessive SCR warmup could be related to the system thinking it needs to increase NOX conversion.

Also, don't discount the possibility of a bad wire. There could easily be a split second where a bad signal is interpreted as a value triggering the warm up cycle. It could happen so fast that it's not seen in the polling interval set in insite.

As far as the warmup cycle goes, I could be wrong, but I thought it ran for a predetermined amount of time once triggered.

I've been in a few trucks that would seemingly get stuck in never ending warmup cycles. Basically any time I stopped for a light it would kick in. Didn't matter what I had been doing prior to the stop either. My current truck was starting to do that before I eliminated the issues so I never had a chance to properly diagnose the cause. I had replaced the DEF doser but that didn't help so I was starting to suspect the outlet NOX sensor but never had a chance to test it.

Both NOx sensors were replaced last year, although new sensors do fail. Outlet NOx 0ppm, Corrected 0ppm. Intake NOx 138ppm corrected 146ppm while operating state is inactive or in warm up.

Outlet NOx Reading Stable Reading not available .. This seems to change when temp is above 335F but it doesn't seem to effect or be effected when in warm up or not.. I'm sure i read somewhere that was normal until a threshold was met.
When Outlet NOx was reading stable Outlet NOx was 4ppm corrected was also 4ppm, Inlet was 134ppm corrected was 142ppm.
I think I will be looking at every wire and plug I can find.