Jump to content

DEF crystallizing at the DPF outlet elbow/flange


manolumber
 Share

Recommended Posts

Like the title says...first, the flex pipe between the DPF and the SCR (compact system) was loaded up with solid crystallized DEF, almost restricted. Changed out the DEF injector in spite of the fact its output measured OK via testing with Tech Tool-thought it might be hanging open at times while going down the road. Truck has since been back in shop twice for def crystal buildup at the DPF outlet to flex pipe front clamp. Double checked the DEF injector using DEF system testing in Tech Tool. Injector checks OK. No SCR codes or problems with regen. The temps are OK during a manual regen. Could find no leaks in the exhaust system. Anyone have any ideas? Thanks in advance.

Link to comment
Share on other sites

Dosing valve

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

Link to comment
Share on other sites

Thanks for the replies.

Crystalline sublimation (sp?) is a process doable thru tech tool which cleans up crystallization in the SCR. That has been done as a precaution but have other trucks without this pronounced buildup outside the pipe in the clamp area after the DPF.

The doser has been changed as a precaution in spite of the original valve checking OK. The new valve was checked for both dribbling/seeping and for volume and checks OK. Once again, no codes indicating anything is wrong with NOX readings and DEF usage volume seems to be normal. We have several of these trucks used under the same circumstances without this problem.

Any other ideas? Dealer techs ever encountered this? Thanks

Edited by manolumber
  • Like 1
Link to comment
Share on other sites

Is the Engine ECM and ACM ( SCR ECM) software been updated lately? There are alot of Mack Product Improvement Recalls going on now about software issuses. Has the truck been in colder than 20 degrees temps for days at a time? Is the lnsulating wrap still on the clamp on the flex pipe behind the DEF doser? We see this problem alot in cold weather. I think the software updates are probably the fix. Im heading to pick up a Fed-ex truck right now with same issue.

Link to comment
Share on other sites

Thanks for the replies. As far as I know the updates have been performed but not absolutely sure. I have access to Fleet Impact on the Mack website. Where would I find a description of the available updates so I can check? Would these be "service bulletins"? The insulating blanket is in place at the clamp.

The ambient temps have been consistently cold with considerable idle time but as stated we have quite a few of these models and they are used under similar circumstances without this excessive DEF cyrstalization accumulation at the front clamp. I`m suspecting there may be a fresh air leak in the DPF outlet causing the exhaust to cool enough to encourage the DEF to fall out of suspension in the exhaust stream and liquify around the clamp and dribbling out to liquify again when it hits ambient air. Does this make sense or would I be getting NOX codes because there is a leak in the system after the DPF? Thanks again.

Link to comment
Share on other sites

  • 3 weeks later...

An update for anyone experiencing the same problem...replaced the DPF outlet/lower pan and absolutely no problems since. I suspect there was a crack at the welded flange of the outlet allowing fresh air to enter and DEF fluid to leak out and solidify at the front clamp. Couldnt see a crack hot or cold but there must have been one as problem solved.

  • Like 1
Link to comment
Share on other sites

Glad you got it sorted. I haven't really heard of that issue happening with that particular curative but if you let me know what the nox codes were I can give you more relevant information, bearing in mind that excessive or insufficient EGR flow causes all of the above madness due to def overdosing to compensate for high inlet nox levels.

I don't know what difference there is with Fleet Impact and ours at the dealer level but the service tab will give you some applicable fsb (narrow to bulletins, no keyword, in additional search values). All service bulletins will appear in EMEDIA at the dealer level, but service newsletters have also covered troubleshooting PPID5396 codes for SCR efficiency, I can rattle off numbers to see if your dealer will fax or email you copies of any you can't find on the dealer portal.

I'll be looking into more tomorrow but it's been slamming at work.

Edited by TRH
Link to comment
Share on other sites

  • 1 year later...

This problem has been covered  on another forum also. I looked for pan cracks but didn't find any. I believe the problem was the flexpipe between the DPF and SCR box. Not that I can locate a crack on it while inspecting it, but in thinking about it, I realized it was the only thing it could have been. ("It" being the cause of having 2 pounds of DEF crystals stacked up between the dosing valve and where the flexpipe begins.) And if you think about it, cool atmosphere has maybe twice the pressure as a 500-degree exhaust pipe, so if there's a hole in it, the atmosphere is going to PUSH its way into the exhaust flow And guess what. When a spray of DEF hits that intruding air, it crystallizes. 

The other thread is here:

http://www.thetruckersreport.com/truckingindustryforum/threads/doser-valve-issues.265189/

 

 

20160928_101726.jpg

20160928_095435.jpg

Link to comment
Share on other sites

I'm getting ready to buy a 2011 CXU613. My shop noticed this during a pre purchase inspection.  After reading this and other threads elsewhere, I'm a little less concerned. Not 100% certain on what to ask of the dealer before pulling the trigger.

 

IMAG4546_zpsjsnseuq9.jpg

IMAG4545_zpszogk3iyi.jpg

Link to comment
Share on other sites

Couldn't quiiiiite be sure of where that white crusty joint you're referring to is, but clearly it's well past the flexpipe we've been talking about. If it's PAST the outlet nox sensor, I would hardly worry. The system won't be paying attention to it. To figure out where the outlet nox sensor is, follow the top of the tailpipe to the first wire you see. That'll probably be it.

Link to comment
Share on other sites

  • 4 years later...

Hi guy's,  I have the same problem on my 2015 volvo d13 it has now 1.2m km on it and I replaced this year 3x the nox sensors 2x def dozer valve the 7th injector 2x the flex pipe just got my dpf and cod cleaned out and a Crack in the pan welded.  I put the heat blanket around the new pipe gaskets and clamps.  Drove for a day and it was leaking again. I'm frustrated with the system.... what else can it be. Have original injectors just once an valve adjustment. Is it a wiring issue or def heater or.............. please help

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...