scr warmup

[Mudflap77]

Hello all, My 2350 seems to want to run in SCR warmup excessively. Today I had a chance to play around with it with insite hooked up.
Start up the truck SCR warm up mode until SCR inlet temp reached 268F Outlet 284F DPF outlet 269F then went inactive.
Put the truck on high idle for 60 seconds inactive. Take it off High idle back into SCR warm up SCR inlet 269F outlet 278F DPF outlet 264F.
Go back on high idle goes inactive again until you take it off high idle.
went for a long drive bobtail starting out while it was in SCR warmup with temps as SCR inlet 269F outlet 278F DPF outlet 264F. Drove for over 30 min SCR temps were both over 410F for about 10 min then it finally went inactive about 3 miles before a stop sign. waited for a couple cars to go by got around the corner back into warmup both SCR temps above 400F for about another 20 min before it went inactive. 5 min later traffic light in town back into warm up.
While doing this warmup BS it will over boost to 40 psi if not watching closely.
DOC/DPF and SCR were changed last year along with turbo and actuator, emissions harness, DEF doser, 7th injector, all emission related sensors.
With in the last month I've done the EGR tune up, pulled the EGR valve off cleaned it spic and span, not a drop of carb/choke cleaner leaks past the valve, I've blown air and cleaner in every port, all were clear. No blockages in the EGR cooler.
Cummins Original file updated while dealing with Regen issues last year. As far as I know there hasn't been another update.
OEM CAC passed the leak down.
I'm at a loss with this thing.

[JimT]

could check for a bad/faulty sensor or a damaged/broken wire for the temp sensors. It's possible there's an intermittent loss of signal. Also double check you ground connection/wires while your at it.

Not sure if any of those temps are calculated, but it does strike me odd that the DPF outlet temp is lower then the SCR inlet temp and the highest temp reading is from the SCR outlet? I'm not sure if it's even possible but, you didn't by any chance disconnect sensors/wires recently and somehow swap them around?

Also, have you inspected the {decomp tube} and can for DEF buildup or leaking? I don't know the design/layout of the exhaust on your truck but it's possible DEF could be building up and absorbing/deflecting heat from a sensor, if it actually is a sensor and not just a calculated value.

There's also the possibility that you have a blockage or leak in the DOC/DPF or exhaust system in general. That would throw the pressure readings off in turn messing up any values calculated from them.

The only other things I can think of is that either the turbo or EGR valve isn't functioning properly to keep the exhaust temps above the minimum threshold without kicking into warmup mode. But, then again, the entire point of warmup mode is to keep the temps up when the engine load isn't sufficient.

Anyway, I only have experience with my 2250 and it's long winding exhaust system underneath my truck. That was before it underwent corrective surgery, so the specifics of your system might be different from the mental model on which I'm basing my thoughts.

[RollinCoal]

Depends on what the truck is wanting to do,
If it thinks it needs a regen it will go into warmup until it hits target temp
Each stage of the engine it will want to see sertian temps there for go back into scr warm up and turn on post injection cycle to make it happen

[Rawze]

I would suggest you post pics or screen shots of the regen history. For all anyone knows, it could be doing exactly what it is supposed to do... as is it actually quite normal for the engine to switch back and fourth between one of its highway modes and one of its temperature control modes while operating.

[Mudflap77]

(05-10-2023 )JimT Wrote:  could check for a bad/faulty sensor or a damaged/broken wire for the temp sensors. It's possible there's an intermittent loss of signal. Also double check you ground connection/wires while your at it.

Not sure if any of those temps are calculated, but it does strike me odd that the DPF outlet temp is lower then the SCR inlet temp and the highest temp reading is from the SCR outlet? I'm not sure if it's even possible but, you didn't by any chance disconnect sensors/wires recently and somehow swap them around?

Also, have you inspected the {decomp tube} and can for DEF buildup or leaking? I don't know the design/layout of the exhaust on your truck but it's possible DEF could be building up and absorbing/deflecting heat from a sensor, if it actually is a sensor and not just a calculated value.

There's also the possibility that you have a blockage or leak in the DOC/DPF or exhaust system in general. That would throw the pressure readings off in turn messing up any values calculated from them.

The only other things I can think of is that either the turbo or EGR valve isn't functioning properly to keep the exhaust temps above the minimum threshold without kicking into warmup mode. But, then again, the entire point of warmup mode is to keep the temps up when the engine load isn't sufficient.

Anyway, I only have experience with my 2250 and it's long winding exhaust system underneath my truck. That was before it underwent corrective surgery, so the specifics of your system might be different from the mental model on which I'm basing my thoughts.

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 same as when things are warming up DPF outlet would be hotter then SCR temp until they some what equalize. As exhaust temp goes down DPF would read cooler before the SCR. My main focus was that there wasn't a large difference between the reading.
The only exhaust related temp that is calculated as far as I can tell, 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

[Mudflap77]

(05-10-2023 )Rawze Wrote:  I would suggest you post pics or screen shots of the regen history. For all anyone knows, it could be doing exactly what it is supposed to do... as is it actually quite normal for the engine to switch back and fourth between one of its highway modes and one of its temperature control modes while operating.

Here is the regen history as requested.

I'm just not understanding why it would be going into SCR warmup when everything is hot. Like coming off the highway under load, parking and 30 seconds later it goes into SCR warmup, or just going to high idle back to low idle it will start SCR warm up again and the SCR temps hadn't changed from when it finish the SCR warmup.
Also when driving while it was in SCR warmup it drove like $hit where as before I wouldn't even know if it was changing operating modes.

[JimT]

(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.

[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.

[Rawze]

(05-10-2023 )Mudflap77 Wrote:  Here is the regen history as requested.

I'm just not understanding why it would be going into SCR warmup when everything is hot. Like coming off the highway under load, parking and 30 seconds later it goes into SCR warmup, or just going to high idle back to low idle it will start SCR warm up again and the SCR temps hadn't changed from when it finish the SCR warmup.
Also when driving while it was in SCR warmup it drove like $hit where as before I wouldn't even know if it was changing operating modes.

regen history looks ok to me at a glance.

What do you mean you don't understand?.. Those SCR and DPF canisters cannot function properly if they fall much below about 450-F or so. IT IS ABSOLUTELY NORMAL FOR THE ENGINE TO JUMP BACK AND FOURTH IN OPERATING MODES TO REGULATE THOSE AFTERTREATMENT COMPONENT TEMPS PROPERLY! ... They cannot convert the exhaust gasses .. and therefore it will not pass an EPA inspection unless those cans stay hot all the time.

THAT IS WHAT IT IS DESIGNED TO DO... Keep the temperatures up and within operating range so that they can convert the exh. gases properly.

-= Sounds to me like you are worried about it actually doing its proper job, and your regen history looks like it is doing its thing as well.

If you want it to switch modes less often, then I would suggest you invest in an exhaust wrap to help keep the temps up.