ISX cm2250 emissions help needed

[dslmchnc]

Thanks for the input. A few things to discuss, i forgot to mention that after it came back from cummins, when they replaced the aftertreatment injector, it ran for a few hours before it broke down again. when i got to it yesterday morning, the active fault codes that it had were, 3375 and 2754. the 3376 never came back after the aftertreatment injector was replaced by cummins. it also logged 2639 3 times in day, and also 1921 once.

Does the ecm compare barometric pressure to the dpf outlet pressure to determine exhaust restriction? after i replaced the dpf my restriction code accross the dpf changed to an inlet restriction code which i never had before. it seems that the dpf was in fact bad and the pressure problem that i have now is a general exhaust restriction flow issue. the dpf inlet pressure too high could also be a restriction of flow across the scr because it is down stream and would make the computer think that it is a dpf restriction. the differential pressure is ok, but the scr being blocked could be like holding your hand over the exhaust, and without pressure sensors across it to give a differential pressure reading, the ecm assumes that it is a dpf restriction issue.

BUT, is there really and exhaust outlet flow issue or is there an inlet/egr flow issue that the ecm isnt seeing, and just assuming that it is an echaust flow restriction?


Cummins said that they suspect the doc of being an issue after they changed the aftertreatment injector. i am not sure why they think that, i cant get an answer about that from them. if it was a temp issue i could believe that it was an ambient temp issue. it was very cold in Maine the day they had it, like -10.

this truck was bought from a local dealer that got 6 of this same truck in a group buy at the end of last year. the identical twin to this truck was bought by another company in this area and they had the same scr issues that we had when they put it into service. the local machine shop has done this scr cleaning many times and apparently its pretty sucessful. the dealer we bought this truck from payed for the repairs as a pseudo warranty. as far as i know the other truck has been fine since they cleaned the scr unit. at first i was sceptical of the cleaning idea. i had never heard of that as a possibility. i thought it was a non-servicable item. this repair has lasted since february, only time will tell if this is actually the issue.



as for the driver who didnt tell us about the coolant loss, he has been let go due to other reasons. i am very aware of the damage that ANY use of a truck with coolant or any other foreign material entering the exhaust is very detrimental to the health of the aftertreatment system. i was unaware of htis issue and since then the drivers have no access to engine fluids and must report any needs to us.


after reading you post response last night, which i greatly appreciate, i removed the scr dosing injector this morning and checked the decompostition tube, i am happy to report that it is clean and free of obstructions. i am starting to lean towards the scr being faulty bacause there are yellow stains around the joints after the injector and the scr, which could be caused by excessive pressure due to excessive restriction. instead of it being soot free gas after the dpf, it is gas now mixed with urea and leaves a trace better that just exhaust.



As for the state of the engine, i have checked for exhaust leaks, intake leaks, the egr valve is clean and functioning properly. the fuel system leakage test has passed within spec and the high pressure, and low pressure fuel systems have no leaks. the fuel filters are regularly changed, and the air filters are also regularly changed.


Last night i removes the egr pipes that link the cooler to the valve and the crossover pipe to the intake and the charge air cooler pipe to the intake. all pipea and passages are clean with a little hint of soot on them. i have seen many egr differential pressure sensors changed beacause of egr issues, when the culprit was actually a clogged cooler, but more commonly the sensing ports were clogged. this egr system is clear from restrictions and so is the intake manifold. i have a bore scope that i ran into the intake and didnt see any issues.

I realize that this engine has very high hours, but the price was right, and the truck fit our needs at the time. i will attach the ten most recent regen files. i really appreciate any input. i think my next coarse of action is to change the intake manifold pessure sensor, egr differentail pressure, egr outlet pressure sensor, and the barometric pressure sensor to rule out any malfunctioning in range sensor issues.

if that doesnt fix it it think the next step will be to remove the scr cata;lyst and replace it. i underwstarnd that i will probably h ave to have it recalibrated afterwards due to updates and i have heard of total replacement kits from cummins that remove a npx sensor. do you know anything about that? not an scr delete, but when they replace the scr unit, other changes must be made i have heard, but maybe thats only on midrange. i dont know.


I dont have any factory trainging on any specicific manufacturer, but the isx cummins are a real problem. we have some newer trucks taht are ok. we also have some egr only engines that are fantastic. i love cummins engine, but the paccar mx-13 engines that we run are better. the only issue with them is the power. i wish they would design a 15 liter engine. we run 100,000 lbs and have been buying all 600 hp isxs lately. the 600s seem to have fewr issues. also the 550 high torques we have are ok.

i would like to take a minute to thanky you personally RAWZE for creating a place where diesel mechanics can get together and help each other out with issues that the dealerships either cant figure out or wont. i look forward to contributing to this forum, both financially and maybe to share some of my knowledge about other things as well. i have worked on many different truck with many different problems. i also work with some very seasoned older mechanics that have TONS of knowledge about older trucks. i would happily answer any questions that i can. feel free to pm me, that goes for anyone.

You are provinding a great service. Thank you very much!
dslmchnc