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JimT

(11-29-2021 )2Nickels Wrote: When the techs were installing the new turbo they commented that my tailpipe was very black/carboned up. I don't know what this means.

That depends. If they are talking about the section of pipe immediately connected to the turbo then that's somewhat normal. If they are talking about the very end of your tail pipe then that's bad. On a 2008 engine you have a DPF that collects the soot. This is what needs to be "regen'd" periodically when too much soot has built up. If soot is making its way past the DPF and out the tail pipe then your DPF or DOC might be no good. IF the DOC and/or DPF are no good this could also be affecting the turbo.

On the engine side of things, if the pipe post tubro is collecting an excessive amount of soot then you could have moisture in the exhaust, possibly oil or coolant (could be from the engine or at that location it could have come from a failing turbo too), OR you could have a problem with the "7th" injector, AKA the dpf doser injector. This part, located just after the turbo, injects fuel into the exhaust stream during DPF regens. It's how the system is able to raise the DPF temp high enough to burn off the collected soot. If this injector is leaking then it could be the cause of the excess soot build-up. It would also slowly coat the DOC and DPF with fuel, degrading their performance and lifespan, clogging up the filter and reducing exhaust flow (thereby increasing back pressure on the turbo) as well as eating/washing away the precious metal coating on the DOC which is needed to create a catalytic reaction during a regen.

Finally, you could have an engine issue creating excess soot in the exhaust. This in turn leads to DPF clogging, excessive backpressure, frequent DPF regens and lots of extra stress on the system (including the turbo). Maybe a sensor reading incorrect, a bad/sticking EGR valve, failing EGR cooler or some internal engine issue. Most likely it just needs an "EGR tuneup" (that's a Rawze term, search this forum and youtube for more details, instructions and videos). Simply put, replace common sensors, clean soot buildup from the EGR and air intake systems and clean any buildup from the dpf doser injector.

The above are all possible contributing factors to your turbo failures. More investigation would be needed to narrow down actual factors. Best bet is to start with an EGR tuneup. Make sure the engine is able to run at its best. Then work your way back. You can disconnect the exhaust pipe from the rear of the turbo and run the engine to visually check soot level. Also, hold a piece of paper in the open exhaust stream to check for the presence of any kind of liquid (coolant or oil) in the exhaust. Inspect the DPF doser for leaks and soot buildup. These are good starting points.

search through the forum, there's tons of dpf, doc and egr related info on here. You'll find plenty of ppl on here willing to help you, as long as you're willing to help yourself.