Diesel Emission Control Systems

The diesel particulate filter (DPF) was introduced In 2007 which was designed to manage exhaust particulates and soot. It’s in your exhaust system to help protect the air we breathe.

The Diesel Combustion Process

This process isn’t perfect. Diesel fuel does not burn completely, it creates soot as a by-product. The DPF is a honey-combed like filter positioned downstream from the exhaust manifold that catches the soot. As soot accumulates over time, the DPF begins to plug-up. A diesel engine requires huge volumes of air for combustion and needs to quickly exhale that air through the exhaust. A plugged DPF creates restriction, which leads to reduced power and fuel economy, eventually choking off the engine completely. This is why people remove the DPF.


Original Equipment Manufacturers (OEM) designed a process called “regeneration” to clean the DPF. Your truck monitors DPF restrictions and automatically begins a regeneration cycle when the pressure exceeds a specific limit, illuminating a DPF-regeneration light on the instrument panel. You’ll probably notice a hot smell coming from your exhaust. It will probably regenerate at this point. The more you drive in town or idle, the more often the DPF will regenerate.

There Are two Methods of DPF Regeneration:

  1. Spray raw diesel fuel into the cylinder on the exhaust stroke after combustion. Diesel fuel injected on the exhaust stroke does not combust; instead, it travels down the exhaust stream until it reaches the DPF, where it combines with soot and burns.
  2. This method uses an injector in the exhaust upstream of the DPF that sprays fuel to raise pipe temperatures.

Both methods generate the high temperatures needed to burn DPF soot.

The first method works well, however, injecting fuel on the exhaust stroke can cause fuel to wash past the piston’s rings and into the crankcase, diluting the engine oil. That’s can be an issue, because diesel fuel and engine oil readily mix which can result in reduced oil viscosity. Trucks with fuel dilution up to 10% might seem low, but a 10% fuel dilution can cause your 15W-40 engine oil to thin to a SAE20. That’s a big reduction in engine protection for engines designed to operate at 15W-40.


To be certain of oil dilution, take an oil sample and have it tested. It’s the best way to know the health of your engine. Also, use Amsoil synthetic diesel oils, they provide exceptional protection for diesel engines regardless of driving style.