[CaptainGizmo]

Steve,
This is Bob Repka. I spoke to you several times last August when I was looking at a 2007 Newell for sale in San Diego. Thanks again for all the info you gave me in that process.

Hopefully you found the problem by now, but if you didn't, consider the following. Its possible that fresh air may be entering the exhaust system between the DPF and SCR syatems. If this is the case, the DEF that is atomized into the system may condense at or just after that point due to slightly lowered gas temperature. If that is the case it will pool and leak leading to crystalization. If any of the remaining DEF is liquid rather than mixed in the exhaust gas, it can pass through the SCR and spray out of the exhaust pipe, as you cited. As an example, check out this link: https://www.bigmacktrucks.com/topic/3879...bowflange/
Did you happen measure the emissions? If you have a base reading you may see a difference as well before correcting this.
Your picture showed a crack in the exhaust pipe near the crystals. Is this area between the DPF and SCR?

Hi Bob!

Yes, I sure do remember you, and thanks for your appreciation!

And, thank you very much for your help with this DEF deal. You've got some good thoughts goin, and all of this may help with the solution.

I have another lead for a guy who "supposedly" has had experience with this, along with a solution. We'll see.

As to your speculation, the "crack" you refer to in my photo is not really a crack, but a clamped joint that's between the crosspipe and the SCR. So, the DEF is sprayed into that crosspipe, then needs to travel pass that joint and into the SCR.

I've had that clamp and gasket replaced, along with the DOSER. So, seems like it would be one of three things:

1. The new doser is still not atomizing the DEF enough
2. The ECM is still overdosing the DEF
3. The clamp/joint is still leaking

To be continued...

[Richard]

I saw what Bob saw in the photo. I am not talking about the joint between the flanges. Look up from the flange. The weld appears to have a crack to me.

[CaptainGizmo]

I saw what Bob saw in the photo. I am not talking about the joint between the flanges. Look up from the flange. The weld appears to have a crack to me.

AH...GOTCHA!!!  Thanks for pointing that out!!

I totally see that now and can't wait to get under there and see what that [crack] is. I'm sure can't be a complete crack, or the DEF would be coming out of it too, let alone present a noticable exhaust leak. But man, that bugs me now! 

I would LIKE to think that the mechanic who was working under there SURELY would have noticed it if it was a crack...right?  RIGHT? 

[xGE_97]

Steve,
Sometimes a small crack can cause an intake of air rather than a noisy leak. It depends on the flow and scavenging effect. The area between the DPF and SCR is insulated by design because of the need to keep the exhaust gasses hot. Too bad there is no sensor here to monitor the temp. Maybe a probe could be placed against the pipe, with the insulation on top. My gut still tells me the problem is here somewhere.

I would be suprised if the ECM by itself is causing heavy overdosing. Maybe something is telling the ECM that the emissions are off somehow. Maybe something to check would be the EGR. Maybe a restriction or cracked EGR itself. I don't think you had a check engine light but there may be codes that show sensor feedback that would tell the ECM to add more DEF.

In any event, the pipe between the DPF and SCR needs to be clear of DEF crystals or there will be a tendancy for additional crystals to form.

You are a super capable guy and you'll soon fix the problem you've been "blessed" with.

[CaptainGizmo]

Steve,
Sometimes a small crack can cause an intake of air rather than a noisy leak. It depends on the flow and scavenging effect. The area between the DPF and SCR is insulated by design because of the need to keep the exhaust gasses hot. Too bad there is no sensor here to monitor the temp. Maybe a probe could be placed against the pipe, with the insulation on top. My gut still tells me the problem is here somewhere.

I would be suprised if the ECM by itself is causing heavy overdosing. Maybe something is telling the ECM that the emissions are off somehow. Maybe something to check would be the EGR. Maybe a restriction or cracked EGR itself. I don't think you had a check engine light but there may be codes that show sensor feedback that would tell the ECM to add more DEF.

In any event, the pipe between the DPF and SCR needs to be clear of DEF crystals or there will be a tendancy for additional crystals to form.

You are a super capable guy and you'll soon fix the problem you've been "blessed" with.

Gee, Bob...thank you for your confidence in me. Actually, ya know...I'm probably more stubborn than capable. LOL But, yuh bedda believe I'm gonna prevail; one way or nuther!

You've got some more great concepts, and YES...I've already pulled that cross-pipe off to make sure it was clear. Not only was it as clean as a whistle, but SO WAS THE FACE OF THE SCR!! Myself and 2 other mechanics inspected it and were happy to see the ceramic element was in great shape.

Stay tuned!  ;-)