MBE 900 Regen Issues

Matthew Owner/Technician Beecher, Illinois Posted   Latest  
Question
Driveability
2008 Sterling Truck L7500 6.4L (MBE906)
Will Not Regen

This truck and I have a long history and I need help! I initially saw this truck over the summer for regen issues, it was not passively or actively regenerating. It was running poorly and had four bad injectors. I replaced all six injector nozzles (not units) and was able to get it to regen. The truck later broke down out of town and had an EGR valve installed. Before I worked on it there was a DOC and DPF installed. Both have been sent back out for cleaning and testing. 

Now this truck is back and will not regen. The truck is in a fail safe mode for soot. Initially it was setting a SPN 3351 FMI 7 for the engine exhaust back pressure valve and the DOC/DPF were not getting hot. I adjusted the valve and the DOC inlet hit 500 and outlet hit over 600, DPF outlet was able to get over 500. The truck is not dosing fuel though. Finally a SPN 3480 FMI 1 for doser fuel supply pressure code set. I did some system testing and found the overflow valve to be defective. We replaced that valve and the base pressure got better, but the doser code came back. Through some more testing I determined the doser block assembly needed replacement. 

The shop replaced the doser block and tried to run a regen, same issue, no dosing. Anyone have any suggestions? I have been pulling my hair out trying to find information and doing testing. I keep finding myself in PSC being told to call Detroit customer support (obviously for the dealers). 

TIA

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Tyler Owner
Gilbert, South Carolina
Tyler
 

So technically it will start a regen, but it will just regen forever? Or will it not even initiate? I'll assume it regens, but just goes on forever and doesn't get hot. So the checks I would recommend. I would start with the fuel system since you already had problems there (injectors), and you've already figured out it isn't dosing fuel. - Fuel Pressure -- Remove the fuel temperature sensor

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Matthew Owner/Technician
Beecher, Illinois
Matthew
 

Thank you, Tyler. I did check fuel pressure at the fuel temp sensor. It was 52 PSI. I also did the fuel flow at the overflow valve and it was within spec. The service info I was using then guided me to replace the overflow valve. I will double check the doser block for leaks when I get there today. I did the fuel volume test you described and it was within spec. I will do the injector test today

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Matthew Owner/Technician
Beecher, Illinois
Matthew
 

Oh and yes, will go into regen but indefinitely. It is getting up to temp enough when it should start dosing but does not.

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Andrew Technician
Commack, New York
Andrew
   

Hey Matthew, I haven't got any experience on the heavy duty Diesels but I'll throw some things out there anyway. I would give priority to the code for exhaust backpressure, backpressure problems will prevent regeneration, I think because it indicates the DPF is perhaps clogged. I don't know how the exhaust flow, pressure, and DPF are monitored in your application but I would look at that

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Matthew Owner/Technician
Beecher, Illinois
Matthew
 

youtu​.​be/KqSix722SK8 See the video. Looks like it is returning too much fuel at the rail. Any suggestions?

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Tyler Owner
Gilbert, South Carolina
Tyler
 

Matthew, email me at …. I'll send you credentials to get into our Virtual Machine and you can browse through all the specs and testing procedures.

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Michael Diagnostician
Champaign, Illinois
Michael
 

Hi Matt sorry been busy, did you get the issue resolved?

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Matthew Owner/Technician
Beecher, Illinois
Matthew
 

Sorry I missed you text last night, busy weekend. The issue is not resolved, unfortunately. The overflow valve, doser block, and compensation valve have been replaced. I believe it may have an issue with one or more injector unit pumps at this point. When I replaced the nozzles I remember the parts guy telling me the units are over 4k a piece. I'm not sure how to prove it out at this point and

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