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i have a mandated 12' ISX 15 800k ,doc and dpf recently cleaned .during a passive regen i get a strong raw fuel smell in cab, smell is only there during the regen which it does about once a day or every 300miles.Cant find any wet looking fuel.i suspect its in the exhaust after 7th but cant find any exhaust leaks.
pressurize everything up and look for exhaust leaks.

also when is the last time an EGR tune-up was done.. including cleaning the Doser injector nozzle in the pipe right behind the turbo?.

people also often confuse a raw fuel smell with leaking valve guide seals... so that is another thing to check into too.
when you say passive regen what do you actually mean? Passive regen is what the truck will do while driving. It uses the EGR and turbo to create higher exhaust temps to burn off some light soot. This type of regen doesn't involve spraying fuel into the exhaust, hence the "passive" part. Active regen therefore involves injecting fuel into the exhaust stream to actively boost DPF temps to burn off more soot. Finally, there's Parked regens. These are like active regens but the vehicle is parked. While active regens still rely heavily on the natural loaded engine operation to generate exhaust heat they are subject to changing driving conditions. Parked regens on the other hand operate in a very controlled manor and are sometimes needed when normal vehicle operation hinders active regen attemps.

I point this out because if you are smelling fuel or seeing a light bluish-white haze from the exhaust ONLY during an active or parked regen then it could either an issue with bad or blocked spray from the doser injector or a DOC that's not catalyzing the fuel properly. The latter is usually due to excessive buildup on the face, an exhaust leak (often from the bellows between the turbo and the DOC) or due to an aged DOC that can no longer keep up with demand. EGR valve and turbo can contribute to the problem as well but (i think) will usually exhibit other symptoms.

Based on you brief description, if that DOC is original, or has 400k miles or more, then it's a strong possibility that it has reached the end of it's useful life. Each time you remove and bake the DOC it does sightly reduce the usable life. From what I've read about 400,000mi is the normal expected life span for these older systems. However, as Rawze suggested, you should first investigate a normal EGR tune-up, check for exhaust leaks, and check/clean the doser injector. While I see why he mentioned the valve guide seals, I would expect a leak there would be evident any time you have a hard pull which heats up the exhaust, not just during a regen cycle.

If the fuel smell is more constant (not just during regens) or more pronounced after long idling then I would focus on other causes such as a bad (leaking) doser injector, bad shutoff or air purge valves for the doser injector, valve guide seals, or leaking injectors.

My own experiences with my 2012 cm2250 have greatly contributed. At around 450,000 mi my system started doing the same thing. Only occasionally at first, usually right at the start of a regen as the temps were still low. Eventually it became more regular to the point where the smoking was constant during regen attempts and all regens ultimately failed, sometimes with high SCR temp faults due to the volume of unburnt fuel passing through the DPF and smoldering inside the SCR can. Although that fault didn't start popping up until later. Eventually around the 540,000mi mark I had no choice but to get rid of that non-functional DOC and DPF. Looking back it's obvious that the system was giving me plenty of warnings that it was failing, but back then I was virtually clueless. I didn't have the knowledge or experience and didn't discover this forum until late.
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