Soot level troubleshooting

2012 VNL D16
I've been having problems with the soot levels all of the sudden. When I drive empty or really light, the levels don't really change much. As soon as I put a decent load on, it climbs quickly and asks for a parked regeneration. There are no codes that pop up, aside from the derate related codes. I've had a dealer perform a regen, and they said the 7th injector and temperatures were all within spec. I've changed the differential pressure sensor and cleaned the tubes. A new flex pipe was installed and the top of the DOC looked fine. A camera was inserted to check between the DPF and DOC and it looked clear. A crystal sub regen was also performed.

If I perform the regen myself, it takes about 30 minutes to complete and the soot gauge is down to <10%. But after about 15-20 minutes of driving, the truck goes back into full derate due to high soot levels. This is usually accompanied by a sputtering knock sound when the truck is running at very low boost levels, kind of like a misfire. The noise sounds similar to how the engine sounds while performing a regen. While derated, the noise goes away and the truck performs great. After about an hour, the soot level falls enough to clear the derate on its own, and it eventually settles around the 45% area or the V in "level". It doesn't seem to raise again at that point, and the noise goes away.

I had the DPF cleaned about 100,000 miles ago, and we don't idle overnight. The problem occurred suddenly and causes a derate too quickly for me to believe that the filter is plugged. I'm going to be taking the DPF in to get cleaned anyway, then put new clamps and gaskets on. In the event that this doesn't fix my problem, where should I be looking next? It seems like since it's related to boost, combined with the noise, that the turbo might be something to check into. Would the discharge recirculation valve also play any role? I've been seeing hotter than normal exhaust temperatures while the noise is occurring and soot accumulates rapidly. Normally I run about 650-700F, but it's been around 800F even while driving with a light foot. Without codes, the shops have been having trouble diagnosing and fixing the problem. Thanks in advance.

 

Well, I'm not running a regen at any set mileage, and it doesn't seem to help at all as it's usually within like 20 miles it asks for another. It's running hot exhaust temperatures even with low boost, between 800-900 while driving, and the soot level is increasing instead of burning off. As soon as it derates, the exhaust temperatures drop to 550-650 and the soot level decreases, and I can drive considerably farther than after performing a regen. When I'm driving empty, I can go 1000 miles and not have the gauge move very much at all, and it settles around the first E in "level". We'll see when I get it apart and have it cleaned and flow tested.

I'm going to get the diesel force cleaning at the next oil change in around 10,000 miles or so. I could get it early, but I want to try and sort out if I've got a faulty component first.

 

Like today, I ran Topeka to Colby, about 300 miles. The soot gauge started at around 90%. Along the way, it went up to the 3, which caused it to derate, and then it gradually fell. I think it was at about 90% when I continued to Limon, another 150 miles. It fell to 20% in that time. The exhaust temps were between 800-900F and that noise was there during the first leg. It was between 650-750F with no noise during the second leg.

I'm not even sure if the temperatures are relevant. From what I've heard, high temperatures are supposed to clean the DPF better, but I'm experiencing the opposite. I wish there was better literature on how the system functioned, written by the engineers who designed it. Right now it seems like the dealer techs go through a checklist for whatever code, and if they reach the end with no conclusion then they start playing email tag with Volvo corporate for solutions.

I'll keep the thread updated as I should have the filter cleaned by Monday.

 

I took apart the DPF and it looked pretty clean. The guy at DPF alternatives went ahead and stuck a pin in multiple spots and said the filter doesn't have a whole lot of ash or soot. I'm having it cleaned anyway since it's apart, and new clamps and gaskets installed, then I'll go ahead and reset the learned data and see where I'm at. Fuel mileage has been slightly down likely due to increased regens, but nothing terrible that would indicate that I've been putting excessive soot into the DPF.

 

I assembled everything on Friday and didn't see any leaks in the DPF or flex pipes. Last time I cleaned it out, there were a few leaks since I only put new gaskets and left the old clamps. I used permatex copper on the inside of the old clamps and it helped quite a bit, but still had a little leakage. But it held up without any issues or asking for a regen for the last 100k miles, so I'm thinking that it's not going to solve the problem.

I talked with the guy at the cleaning place for a bit after getting my filters back. The way that the system has always been described to me is that the sensor measures the difference in flow between the filters, and that is how it determines if it's full or not. But it sounds too simple, like you could just put the sensors in a pipe and create a slight restriction to fool the system into thinking it's always running good. I always suspected that it uses the data from the sensors and compares them to a preset map stored in a control module, which compares flow rates under certain conditions like throttle position or boost levels, and then has a tolerance + or - to determine if the data is within specifications. He said that's exactly how it works.

I'll give an update after I get the truck on the road. Unless I go up into the mountains empty, I'm going to have to wait until tomorrow to grab a load so I can test it properly.

 

Drove empty for 1000 miles, soot gauge stayed around the 35-40% area. Got loaded and heading back, and around 400 miles into it the soot gauge is showing 100%. I cleaned up the 7th injector while I had everything apart, so we'll see if that helps bring it back down from the A mark. Since it was within spec during regens, I don't believe it's going to help.

Anybody have any ideas on what to check next? I'm getting to the point where I might as well start throwing parts at it and hope it fixes it.