Volvo DPF Pressure

[RHeller11]

Been fighting a DPF pressure issue for a few months and cant seem to figure it out. New DPF filter,recently cleaned DOC,new pressure sensor and new temp sensors. I am getting .25 dpf pressure at idle after a regen. This was happening with 2 different DPF filters. Shop hooked up a pressure gauge and got 1.4psi at 2100 rpms. I have taken both pressure sensor tubes off, cleaned and verified no leaks. I cant for the life of me figure out where this backpressure is coming from. any insights would be greatly appreciated!

[Rawze]

what year, make,model truck? what make/model engine?

have you checked the decomp tube? - does it even have one?
http://rawze.com/forums/showthread.php?t...07#pid1807

have you taken pictures of their faces after running a while?


Has the DOC/DPF been de-ashed and flow tested on a machine?

[RHeller11]

Its a 2011 Volvo VNL D11. I dont have a Decomp tube. The DPF is brand new, however the old one that was just cleaned along with the DOC did the same. Both the DOC and old DPF flowed to OEM specs according to cleaner. So I just took voltage at the DPF sensor and am getting .615 volts. My soot level on the dash says 95% full. I thought the range for the dpf pressure sensor was 0-5v...that would make the actual soot level low correct?

[Nilao]

Has a maintenance reset been done? I know its a volvo engine but surely it has to be told the dpf has been replaced.

[RHeller11]

(05-22-2019 )Nilao Wrote:  Has a maintenance reset been done? I know its a volvo engine but surely it has to be told the dpf has been replaced.

Yes, a reset was done, actually a few times now.

[TruckDoctor]

Keep in mind unlike Cummins, Volvo doesn't check pressure after the DPF Outlet, nor do they have a exhaust pressure sensor like a Cummins. If you plumbed a pressure gauge to the inlet "DOC" section of the DPF (usually a 1/8 pipe plug fitting) you are checking complete Exhaust System Back Pressure. Being a US10 emissions truck with DEF and SCR system you could have a clogged SCR inlet pipe, or SCR Catalyst causing overall high exhaust system back pressure. Being there is only a differential pressure sensor on the DPF it could have 1.4 psi on the inlet and say 1.2 psi on the outlet side which is still going to make your differential pressure sensor seem to be "in spec" doesn't mean overall system back-pressure is to high. 1.4 psi at high RPM doesn't sound crazy through the moon. I've seen worse. Is the truck asking for regen's all the time? Also if you were to map a US10 emission Volvo with a laptop it quickly will get to around 100% soot load and its not an issues. Those trucks will do active passive regen's sometimes up in the 130% range. 100% on the dash usually doesn't even ask for a forced parked regen yet. US10 D11 Volvo can regen up to 200% soot load before needing a maintenance reset. I'd make sure have someone regen it with laptop and make sure you have roughly 55k-65k for turbo speed and T2 and T3 temperatures between 850-910 degrees. US07 trucks were hotter and they brought the temps down for a few years. Now US17 trucks are back up regening around 1100 degrees during what they now call a "sulfur regen"

[RHeller11]

It doesnt ask for a regen very often. I last did a regen at the shop while hooked up to laptop 2 weeks ago. Mind you, this is with a brand new DPF filter and recently professionally cleaned DOC filter. I had t1 temps at 700, T2 temps at 920 and T3 temps at 928. DPF pressure started at .44 psi and ended at .17psi. my soot level was at 11% when done. Proceeded to drive approx. 200 miles and soot level was back to 100% where it would finally passive regen to about 85%. This has been that way for last 2 weeks. I checked the voltage from dpf sensor going to control module and I got .615 volts. I then unhooked the SCR inlet tube and got .61 volts at sensor. I think this is telling me my SCR is not causing a backpressure issue. however, I thought the output of the DPF sensor was .5 to 5 volts. if thats the case, the 100% soot level on dash is not matching up to what the dpf sensor is putting out.

[TruckDoctor]

Sorry for the delay in responding to your reply. Volvo is a little odd with its "Soot Level" calculations. I'm not sure the laptop you are using, but you can also go into Aftertreatment History and see the characteristics of the truck and what causes most of the regens that the truck has done and also the DPF Differential Pressure sensor in relation to time the truck has been driven. It will give you the amount of hours the truck has say been driven and the DPF differential pressure was 0.43 psi for 2349 hours of the trucks operation vs say 1.46 psi for 3.4 hours of the trucks operation for the life of the vehicle.

US07 trucks and especially the spark assisted systems used on garbage trucks tend to go from 0% to 100% in a 6-8 hour period of operation and will either do a passive or request a forced regen.

US10 emission trucks are kind of fishy and a little different its hard to explain it, but I've performed a manual regen on a truck and seen the soot level go from 13% back up to 100% soot level in a very short time even though the dpf diffential pressure sensor was reading great. it however didn't ask for manual regens or gave no warning. the 100% threshold in the US10 emission truck is different. Its as if they want to keep it up in that range. I don't believe they passively do regens until 130% soot load while say driving down the highway.

Based on what you've listed. the fact that you did a manual regen and haven't been requested to do a parked regen for over 2 weeks and your voltage reading is only 0.61 volts and you have low differential pressures. I'd like to say you don't actually have a DPF/Regen issue at all. the T2 and T3 temps being around 920 is also great. I think the 100% soot load is tricking you. It make sense cause its tricky to me as well. Not sure why they have a 200% threshold. How does a filter get clogged to 200% of it? how does anything simply exceed 100%.

When US10 trucks start having Regen, Pressure, or Regen Temperature issues you will be getting prompted to do more "Parked Regens" if you don't get this what so ever, I'd say the truck is fine at this time. 1.4 psi of total exhaust system back-pressure is also okay.

[TruckDoctor]

I'm also curious why all these parts were replaced? Sounds like someone who isn't familiar with the values on these specific type of truck is working on it throwing parts at it.... I may be wrong, but unless you actually had a "Check Engine Light", Fault Codes, or symptoms to cause you to think you had an issue.. What made you believe all these parts needed replacing? If you did in fact had a clogged DPF or Catalyst... after replacement what makes you still think you have issues? Is someone misinforming you?