Dreaded SPN 4094 FMI1 NOx inducement fault NEED HELP!!!

[Wasteman1]

I have a 2012 Mack with MP7. have codes SPN4094 FMI 1&18. SPN 5246 FMI 0, 15, 16. Code 4094 FMI 1 is the only one active now. i have seen past threads on this. 13PSI boost, temps all good, around 900. DPS .13  I have done many regens. new outlet NOx sensor and DEF doser. . DPF not passing soot. Decomp tube completely clean and clear. NOx drops down to around below 100 then comes back up to 200 after regen. the DEF doser says its dosing but the tank level never goes down during the regen it said is was dosing 10% but NOx stayed at 510. i have done all the dosing tests they all pass and the doser is spraying fluid out and amount seems correct (when testing the tank level goes down.). Truck is hard starting and probably needs injectors and cups but it has been that way all summer and not had SCR codes. after regen NOx is steady at 230. rev to 1500 and it goes down to 100. then idle it dips to 90 but then back up to 230 DEF dosing valve percentage stays at 0 after the regen. 

Edited January 10 by Wasteman1

[Wasteman1]

ANYONE? the truck says it's dosing at 10% during a regen but the tank level never goes down.  new inlet NOx sensor and still nothing. doses fine on all the test modes but it isnt dosing normally. need help!

 

[Mackpro]

There was an older service bulletin on the 4094 that was very helpful but I don’t have it with me. Something often over looked is the EGR system, mainly the EGR differential  pressure sensor and it’s common problem of port clogging. There are updates for the MP7 venture pipe, tubes and sensor. When the ports clog the Engine ecm sees low EGR flow and commands the EGR valve to open more and  can cause the 4094 code. DEF usage and dosing percentage varies based on engine load and other factors so don’t look to much into that. Also on pre-OBD ( 9 pin diag connector) I was told by Mack Tech Support that the nox readings  that you see might not be always what the actual readings are and what the ACM actually sees. Also the exhaust stack outlet should be clean with no soot or darkness. Any soot passing the DPF will cause high NOx . The pre-OBD 4094 and the 2013+OBD  P20EE00 codes are pretty much the same. Which is their way of saying “ You got high NOX and we don’t know why and you figure it out”. Usually on OBD trucks the the outlet nox will be 1/3 of the inlet when dosing. Message me your email and I’ll see what bulletins I can find to send you. 

[Wasteman1]

we took it to Mack they replaced the EGR cooler and EGR diff sensor and Venturi tube with new. they said it needed injectors. we replaced the injector and still the same problem. we have now replaced the ACM but Mack programmed the new one with the old ones program. it still id not dosing unless your in test mode, then it doses fine. 4094 will not go away, it is still not dosing. we are trying to get a used ACM from a good working truck. 

[fjh]

On 1/10/2024 at 11:11 AM, Wasteman1 said:

we took it to Mack they replaced the EGR cooler and EGR diff sensor and Venturi tube with new. they said it needed injectors. we replaced the injector and still the same problem. we have now replaced the ACM but Mack programmed the new one with the old ones program. it still id not dosing unless your in test mode, then it doses fine. 4094 will not go away, it is still not dosing. we are trying to get a used ACM from a good working truck. 

Did they sweep check the turbo? if the turbo is sticking it is a viscous circle as far as soot production ! not enough air more soot! round and round! 

[Wasteman1]

we know the problem is the DEF doser is not dosing and that's why the NOx is high. you do the Doser tests in tech tool and it is dosing fine in test mode. so we know the pump, lines, doser are good because they work in test mode. in normal operation, it says it is dosing at 10% or whatever but the tank level never changes. we are waiting for a used ACM out of another truck right now.

[Wasteman1]

put  in used ACM today and did 4 regens, same issue. says it's dosing 10-15% and tank level never goes down. 4094 fmi 1 still active. ordered a new DEF pump now. i was reading in tech tool and it said the ACM sends signal to the DEF pump and the internal electronics of the pump deciphers and adjusts dosing amount accordingly.  doesn't make sense to me that it works on all the tests but not in normal operation. not all repairs make sense i guess. just throwing parts at it since i don't know what else to do. 

[Wasteman1]

Replaced the DEF pump and it is still doing the same thing. took back to the dealer. they said the CAC is cracked. they changed that. nothing. now they say the SCR is bad. i doubt it but that's what Mother Mack wants them to try next. i bet money it does nothing. going on 3 months this truck has been down. i just can't wrap my head around it. the computer says it is dosing DEF at 10-13% at times but the level never goes down in the tank, but you do the dosing tests and the DEF doser sprays fine. just don't get it. I am almost wondering if there is some kind of electrical interference when the engine is running. dosing tests are done when it is not running and it works fine. I bet/hope Mack will send engineers out on this one.  NOBODY can figure it out.

[The Heinz]

I'm by no means qualified, but it sounds like your SCR might be dead. Pretty much every truck with 4094 that rolls in our shop leaves with an SCR. There were some times new NOx sensors resolved the issue, but most resulted in the truck getting a new SCR. Did you use an OEM NOx sensor? Most aftermarkets we tried ended up not working, to the point our shop won't use them at all. 

Edited February 14 by The Heinz
Wording

[Justinizme]

Was the issue ever resolved? What ended up being the culprit?