CM 871 getting 3.6 MPG

[JimT]

Sounds like the constant regens are killing your mpg, which is already lower due to heavy loads. So the question is why are you having so many regens? Here's my thoughts based on your description and having been through this myself. I would go down this list, checking each in order.

* Excessive soot production from the engine leading to the need for more frequent regens. This one is easy to check, just disconnect the exhaust pipe from the back of the turbo and observe the exhaust. Even if it isn't noticably sooty hold up a piece of white paper behind the exhaust coming out of the turbo and see if any oil or fuel residue collects on the paper. If so then this is also what's collecting on the DOC and DPF. Causing exhaust restriction and poor oxidation, leading to more frequent regens and the white smoke at the start of a regen.

* Exhaust leaks. This leads to inaccurate sensor readings which screw everything up. From the back of the turbo to the end of the DPF it all needs to be free of exhaust leaks. Could be the cause of the white smoke at start of regen. Could also lead to unneeded regens due to inaccurate sensor readings.

* Leaky DPF injector, bad/leaky purge air actuator. Some extra fuel leaks or drips into the exhaust when regens are NOT being performed. This coats the DOC and maybe the DPF. Simultaneously reduces the oxidation ability of the DOC while also raising the exhaust restriction. This residue smoldering while regen temps are being raised could cause the white smoke at the start of a regen. Also reduces the longevity of the DOC and DPF.

* DOC and DPF are shot. For whatever reasons the DOC and DPF have reached the end of their functional life and need to be replaced. The white smoke at the start of the regen is a good sign that the DOC isn't properly oxidizing the exhaust and the injected fuel is not burning properly until temps have risen enough. It starts small but after time the smoke will get worse and worse and worse. Eventually active regens won't ever get up to the right temp to burn clean. Then parked regens will be needed. All the while further reducing the remaining life of the DOC.

* Sticky EGR valve. Last on my list, but any irregularities in EGR gas volume can lead to improper fuel/air mixture in cylinders leading to poor combustion, extra soot production and exhaust temps that vary from what the ECM expects. Could be the cause of the white smoke at start of regen. Could be causing excess soot which clogs up the DPF (and maybe starts to faceplug the DOC) faster then normal. *** This could be a cause of excessive soot production, but is fairly expensive to replace so make sure there isn't a different cause first ***



If you only see a few puffs of white smoke right now then it isn't bad, but IT WILL continue to get worse. Eventually the DOC and DPF will need to be replaced, regardless what the underlying cause was. It took my tractor about a year and a half (about 120,000mi) from the first white smoke signs to complete inability to regen. I tried many things in the process and the above info is built upon my hindsight. I was averaging 5-6mpg while I had these issues, but I typically ran on the light side. Sometimes I would have all day long regen attempts while driving. Once I rid my truck of this system the fuel mileage averaged mid 7's. Up and down depending on my day to day driving habits. So yeah, those regens are absolutely killing your mpg!