Calamity Part 3: It Gets Worse

On Tuesday August 13 our DOC (Diesel Oxidation Catalyst) arrived.  The next day, Wednesday August 14, the coach went back into the service bay for installation of the new DPF and the DOC.  About noon that day we get a call from the shop that there is a problem.  The DPF is secured to the after-treatment unit and to the frame with a large stainless steel circular clamp, much like a very large hose clamp.  Each end of the clamp has a welded loop holding a T-bolt and corresponding screw.  During the removal of the DPF clamp the mechanic broke the T-bolt.  CRAP!

Here is a look at the DPF clamp

Here is another look at the clamp installed

Broken T-bolt

The DPF clamp is a Freightliner part, rather than a Cummins part.  Cummins says the DPF clamp is on back-order at Freightliner and won't be available for at least 7 weeks.  WTF!!!!  Without this clamp we are dead in the water.  The service advisor, the service manager, the mechanic and I are looking at the part, looking at each other and scratching our heads.  Perhaps the clamp can be repaired?  The T-bolt cannot be removed without drilling out the welds and spreading the loop at the end of the band.  Then the clamp loop must be welded back together after installing a new T-bolt.  Unfortunately this shop does not have the equipment to weld stainless steel and would have to take the part to another shop.  In the end they are able to find a different but similar clamp from which to harvest a T-bolt, drill out the welds, install the new T-bolt and take the clamp out to be welded at another shop.  Crisis averted.  At least this crisis.

Freshly welded DPF clamp

DPF clamp showing new T-bolt

They put everything back together, new DOC, new DPF and all the appurtenances. Per Cummins protocol they performed post-diagnostics tests, which included an "air handling test".  The air handling test failed, and they ultimately determined the turbocharger is shot. Apparently they now believe the turbocharger failed, taking out both the DOC and the DPF. Can it get any worse?  There was only one turbocharger available in the US, and they ordered it for us.  It was expected to arrive tomorrow (Thursday), but we wouldn't know for sure until tomorrow AM, when we could check the tracking info.  If it does arrive tomorrow they might be able to install and complete repairs tomorrow.  At this point the repair estimate is becoming huge.  I mean max-out-all-the-credit-cards and call-my-broker-to-cash-out-my-stocks huge. 

But alas, the turbo did not ship this day in fact was delayed for several more days.  The saga continues ....

In the meantime a little information for those who might wonder:  DPF, DOC, what do all these acronyms really mean? What does the diesel after treatment do and how does it really work?

The harmful emission gases in the exhaust stream move from the exhaust side of the turbo to the aftertreatment system (outlined in red).

The Cummins Particulate Filter contains the Diesel Particulate Filter (DPF) which collects and oxidizes carbon to remove particulate matter (PM) by more than 90%; the Diesel Oxidation Catalyst (DOC) aids in this process and is also contained in the Cummins Particulate Filter. The exhaust passes from the turbo through the DOC and enters the DPF.

After collecting the particles from the gases in the DOC and DPF, there is still nitric oxide (NO) and nitrogen dioxide (NO2) left in the exhaust. In order to reduce the NOx levels a light mist of urea (Diesel Exhaust Fluid (DEF) or AdBlue) is injected into the hot exhaust stream in the Decomposition Reactor.

The exhaust progresses from the Decomposition Reactor into the SCR system which converts the toxic NOx and urea mixture into harmless nitrogen gas (N2) and water vapor (H2O), which effectively eliminates harmful emissions resulting in near zero emissions from the exhaust.

Click HERE to view a short video illustrating the process.