Frequent Regen Research
I wanted to share some research I have been doing, I'm always open to suggestions, comments, and questions. I have been seeing quite a few trucks with codes for frequent regens. The aftertreatment system on these trucks is fine. The engine is producing increased emissions causing the DPF to require frequent regens. There have been quite a few that have me scratching my head. These vehicles go beyond the injector with stiction issues, bad electrically, etc. What I have been finding is dirty pistons causing increased emissions. The fuel is not able to swirl the way it is supposed on the piston and causes turbulence, creating an incomplete burn. Apparently the International dealers by me see this all the time. The way they diagnose it is by pulling the cylinder head and starting an in-chassis... I have been trying to find a better way.
I have attached some pictures that are DSO waveforms looking at exhaust pulses with a First Look Sensor. The blue channel is injector current, the red channel is the exhaust waveform. I recently worked on a 8600 with a N13 (International engine with Cummins aftertreatment). Initially I fixed an SCR issue. Once that was fixed the truck came back a 1,000 miles later with a frequent regen code. I scoped the exhaust and found it very turbulent. We suggested the customer drive with some fuel additive for the next few over the road trips. A couple weeks later I looked at the truck, and while the waveform wasn't perfect, it was much better. The MIL did not come back on. I still need to do more research, but I believe this is a much better way to find these dirty pistons than pulling the cylinder head.
Matt, not sure on the heavy duty side, but on the small engine side I deal with air filter issues all the time. I can have a new L5P duramax with 800 miles and start setting codes for regen, quality, frequency, you name it. And the air filters are either badly restricted or sucked in. The issue with our is the "new and improved" hood scoop. Oh and if they use a aftermarket filter... I have a much higher/more frequent failure rate.
Yes, we see air filter issues on HD vehicles too. Those have been easier for me to find. I am trying to find ways of discovering coking issues without cylinder head removal now. This stuff is experimental at this point, me playing around... not enough to use as a diagnostic tool just yet.
You not teaching at COD anymore? I will be interested to see what you come up with. I am sure the light duty side is going to run into the same issues, if they have not already and I am just not seeing it. Being mostly farm trucks around here, its usually a induction issue.
Still at COD full-time. Part-time mobile diag/programming and fleet shop at house.
Non-scientific opinion here but from what I saw at the shop was more indicative of the type of driving the truck was subjected to (and it's mileage) than any other factor. I saw the trucks that did more driving in traffic have frequent regens and short oil life. A forced regen (or two) would usually make a notable difference in both the regen frequency and oil life.
I have seen those too, but some of these are over the road trucks. Something is wrong on the engine side causing the DPF to load up too fast.
Matt, did you look at the fuel itself to see if it was black by any chance? I see a lot of cases of asphaltene in the fuel systems.
Matt on these problem Trucks are the Docs getting up to proper operating Temp? Are you finding any exhaust leaks? Another thing you should check is your base engine timing. On a Convential Diesel I synch a injector with current to starter current and see if anything looks off and I also put a pulse sensor in the intake and the exhaust.🙂
Everything else was good on this engine. Didn't get a better sync, harness is sealed up pretty good on these. No problems with anything aftertreatment, DOC and DPF light off and all temps look good. There is a long list of issues we see cause the frequent regens, seems to grow everyday. I just want a better way to prove these coked up pistons out.
Well I know it's not exact but if you do a base engine timing check with the scope showing starter current and the current looks uneven, some higher than others that can either indicate coked up pistons or a timing, valve adjustment, or valve issue. Plus I also use the pulse sensors to verify this to make sure I dont have a starter or flywheel issue. Then once that's confirmed I check the overhead and if that's ok we try a cleaner through the intake and exhaust. Fyi on the cleaner, If it's a hi mileage engine sometimes chunks of carbon can go through the exhaust and make Vgts stick. I have experienced this myself. So if you attempt this type of repair warn the customer about the consequences. If you'd like maybe sometime I could come up and assist you and see what your dealing with and show you how I go about these issues.🙂
Thanks! What cleaning system are you using? I have a truck to look at tomorrow that has been having frequent regen issues. A bunch of other things have been fixed on it. It has a MBE 900 that won't get hot enough to start dosing fuel though. If I don't see any EGR issues tomorrow morning I will do the testing you laid out.... might have to use the phone a friend 😉
It's called Diesel Force. It also uses a tablet that pwm the Egr Valve and the Turbo Actuator. Here is a pic.