Reputation of the Diesel Engine
It is believed that 50% of the pollution in America is a direct result of combustion engines. The diesel engine is among the most problematic. Despite the diesel engine’s reputation for being highly efficient and surpassing gasoline engines in the miles per gallon scale, these vehicles noticeably emit black soot into the air during heavy acceleration. The particulate is highly carcinogenic and can now be captured using a simple filter on the exhaust. Thankfully, the selective catalytic reduction (SCR) method that followed DPF works without the problems the DPF suffered.
Section 203 of the Clean Air Act makes it a federal offense to tamper with a DPF or remove it. The arguable exception to this rule is if the owner only uses it off-road. This is why many companies who are willing to remove DPF’s require the owners to sign waivers swearing that it will be used solely for off-road purposes. The other problem is that any diesel truck with a DPF removed will immediately fail emissions inspections. In other words, while the DPF law may be difficult to enforce specifically against truck owners, you will run into complications with state officials if you remove it or tamper with it in any regard. The best advice to follow is do not DPF delete if you want to remain worry-free.
Regeneration Cycle Problems
The problem with the DPF design chiefly boils down to the regeneration cycles. If the DPF does not reach the correct temperature in a passive system because the truck never reaches sufficient highway speeds, then the passive system is virtually worthless. A passive system may use a platinum metal substrate much like a catalytic converter to react. In both instances, a vehicle will fail emissions if the exhaust does not reach sufficient operating temperatures on its own volition to burn off the trapped combustion byproducts.
The active regeneration systems are even worse. An active regeneration system typically uses a variety of methods to heat up the exhaust when the filter is getting clogged. A clogged filter creates excessive backpressure that reduces engine performance. The PCM may inject fuel, retard timing, increase EGR flow, throttle the intake, or increase turbo boost to heat up the exhaust. Injecting fuel is the most troublesome method because it wastes fuel and strips away the film of oil protecting the delicate internal surfaces of the engine. Premature engine wear and carbon buildup from incomplete combustion are possible symptoms of active regeneration.
Worst of all, when a vehicle enters active regeneration mode, it may be limited to speeds as low as 5 MOH. If the vehicle is off when the regeneration mode begins, it may not be able to restart. Fires have even been reported when people parked their trucks in tall grasses and the regeneration mode heated up the exhaust in excess of 1000° F.
The other major problem is that even the fine ash needs to be cleaned once a year. This is highly problematic for a number of reasons. First, owners must locate a shop that is equipped with a special machine to clean the DPF. These machines require removal of the DPF to flush out the highly carcinogenic fine ash by using compressed air and vacuum.
Exhaust parts are difficult to service in the first place. Many exhaust systems are already oxidizing by the time they hit showroom floors on domestic vehicles. Places that do work on exhausts usually have to reheat the metal using torches to break up any unions. If you throw in corrosion from road salt in the northern states, you are looking at a service nightmare. The exhaust parts may rust-weld into place and require a complete replacement of the entire exhaust system to simply remove and service the DPF. A new exhaust system on even a late-model light-duty diesel pickup truck can cost as much as $8,000.
An Overview of Removing DPF
The DPF removal requires access to the powertrain control module (PCM). The PCM must be reprogrammed to terminate the regeneration cycle and to disable any electrical components of the DPF system (such as exhaust injectors and temperature sensors). Afterwards, a straight pipe exhaust system can be custom fabricated, premanufactured, or retrofitted to the downpipe of the original exhaust. Removing the DPF may increase fuel efficiency by as much as 7 miles per gallon.
- Substantive Increase in Performance
- Substantive Increase in MPG
- Lower Maintenance Costs
- No Fire Risks
- Less Wear and Tear on Engine
- No Hassles from ReGen Cycles
- Voids Warranty Coverage
- Limits Use to Off-Road
- Arguably Illegal in Any Case
- Increases Pollution
- Automatic Failure at Inspection Stations
- Requires PCM Reprogramming
Remember you can also just clean the DPF filter.
The DPF system was poorly engineered. Although it looked great on paper, it did not fully consider how it would impact drivers in the real world. This is a traditional problem with engineering because it is only half math, physics, and science. The other half is pragmatism of how well it will hold up in real-world driving conditions and the diversity of applications drivers will encounter. It is a breath of fresh air to see that the EPA is taking steps to clean up pollutants. However, the DPF’s should be recalled and replaced with selective catalytic reduction (SCR) systems.