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Diesel emission systems and the future!!! Part 2 – DPF

Hey guys back again for part 2. In part 1 we covered EGR systems which were introduced in order the “recycle” spent exhaust by cooling it and reintroducing it back into the intake mixed with fresh air. The EGR system lowers combustion temperatures and reduced NOX emissions. In 2007 more regulations were introduced that required vehicle manufacturers to reduce the amount of soot (particulates) in diesel emissions. This required a lot of planning for solutions since, soot “black smoke”, has been common in diesel engines since their inception because unburnt diesel fuel in large particles comes out in the form of soot. This mandate gave birth to the creation of the diesel particulate filter (DPF). A DPF is a filter that is installed in the exhaust pipe after the turbo and before the tailpipe. Inside a DPF is a collection of metals in a honeycomb core. This core traps soot particles in the exhaust to prevent them from leaving the tailpipe. This filter, not unlike other types of filters, will eventually become restricted with particles and will need to be cleaned out. The process by which the filter is normally cleaned is called “regeneration”. Early means of regeneration for Powerstroke, Cummins, and Duramax all involved “post-injection”. Post-injection involves firing the fuel injectors on the exhaust stroke in order to send hot unburnt fuel straight to the DPF in order to burn out the soot particles. This “post-injection” strategy was successful at burning out the soot but caused widespread issues as well. The engine sending fuel into the cylinders on the exhaust stroke caused fuel to get past the piston rings and causes “oil growth”. In many cases the engine oil level would become overfull and could cause a “run-away” condition or cause engine damage on the bottom end. Also this hot (1200-1300) exhaust has to go through the EGR system and turbo before reaching the DPF which causes additional wear on these components. These early DPF systems were laden with problems and caused many trips to the dealer for customers!! Now we will look at the big 3 individually.

2008 Powerstroke emission system-

In 2008 Ford introduced the 6.4l Powerstroke engine. The 6.4l had 2 huge goals hanging over it’s head: 1. Improve on the 6.0 2. Meet new EPA guidelines

The 6.4 Powerstroke is equipped with 2 EGR coolers (vertical, horizontal), 2 turbochargers, a new common-rail fuel system, an EGR valve, a DPF, an intake throttle, a diesel oxidation catalyst, and a converter. These emission components combine to clean up the NOX and particulate emissions to meet the 2007 guidelines. The 6.4 used “post-injection” to actively regenerate the DPF when it became restricted with soot material.

Below is a pic of a 6.4l cat/DPF assembly. Pic is not mine!


Problems: The 6.4 was plagued with problems in the emission system as well as the engine. The early DPF systems across the board tend to be the most unreliable years to own since the “post-injection” method was being used and SCR had not been introduced yet. The 6.4 suffered from ruptured EGR coolers, sticking EGR valves, defective exhaust temperature sensors, clogged DPFs, and oil growth. Oil growth is so bad on the 6.4l that it has been known to cause lack of lubrication because of fuel dilution which can cause damage to engine bearings as well as rocker arm pivots. The most pronounced downfall noticed by owners is just how low the fuel mileage is on the 6.4l. Because of the post-injection process fuel mileage on the 6.4 can be as low as 12 mpg unloaded and 7 mpg when towing. This is a huge decrease from previous engines and can be the most frustrating of all to a new diesel owner.

Fixes: The fixes for the 6.4l Powerstroke are very similar to the 6.0 fixes. There are “delete” options that are not street-legal but they do offer a solution to oil-growth and loss of longevity in the 6.4 Diesel. Unfortunately for owners, the emission solutions available involve fixing this DPF system which is a bad initial design in most peoples’ opinions. Aftermarket EGR coolers can be purchased for the 6.4l from Bulletproof diesel and these give you a lifetime warrranty as well as not altering your emission system in any way. The EGR valve however doesn’t really have an upgrade available but the 6.4 EGR valves are much more reliable than the valves on the 6.0. The DPF doesn’t really have an aftermarket as well that will cut down on any of the engine issues. The regen process is really the culprit here since the diesel fuel that seeps into the oil pan is normally what causes runaway conditions, worn rocker arms, and engine bearing failure. When the engine gets overfull the extra oil will make it’s way to the intercooler where it can build up and be sucked into the turbo causing engine damage. Unfortunately if you have a 6.4 diesel you will have to choose between deleting it for reliability or maintaining it religiously to ensure oil growth doesn’t get out of control.


2008 Duramax emission system-

In 2007.5 the LMM Duramax was introduced. The LMM has an EGR cooler and valve as well as a DPF. Like the 6.4 Powerstroke, it used (late or post-injection) to send raw fuel to the DPF to clean it out and burn out soot. This causes the same issues of oil growth and washed out cylinders that the 6.4 Powerstroke experienced.

Problems: The EGR cooler and EGR valve on the Duramax are high failure items and due to the post-injection method of regen this year model suffered a horrible loss of fuel economy from previous years. The DPFs in these year trucks would fail internally as well resulting in a loss of power and engine stall.

Fixes: The fixes for this year emission system are very similar to the 6.4 fixes. You’re either gonna end up deleting the emission systems and gaining 30% fuel economy or you will be replacing DPF and EGR components as they fail. I know this doesn’t sound very optimistic but to be honest these year engines don’t really hold value well since the previous years and later years get better mileage and reliability.


2008 Cummins emission system-

The 2008 Dodge trucks with the Cummins engine were introduced with a DPF, EGR cooler, DOC, and NAC (Nox absorption catalyst). The NAC stands out here since it is only used on the Cummins. It is essentially a precursor to the SCR catalyst that comes in later year engine. The NAC converts NOX to nitrogen and oxygen by capturing NOX in lean conditions and converting the gas during rich operations. This catalyst had to be regenerated as well to remove sulfur from the catalyst with a 3-5 second regen process that occurs every few minutes. The DPF also requires a regen when it gets full as well.

Problems: Very similar to Duramax and Powerstroke with even more of a loss of fuel economy. Due to the NAC needing to be cleaned the engine will burn more fuel in a shorter amount of time. Also the early regen strategies in the ECM were less than optimal and would sometimes require long drives to successfully clean out the DPF.

Fixes: The 6.7 2007.5-2012 is a great engine but is plagued with DPF related failures. Deleting the emission system is an option but if you want to keep the emission system a necessity is updating the ECM. The newer ECM strategies help with regen issues and can help reliability going forward.


Stay tuned for part 3 where we tackle SCR!!! Thanks for your time!