What is a particulate filter or DPF, why is it on there, and can I remove it?

This is a question we get a million times a day.  Since 2007 all Dodge Cummins 6.7, Ford Powerstroke 6.4, and Chevy Duramax 6.6 trucks come from the factory equipped with a particulate filter to meet tougher emissions standards.  A diesel particulate filter (DPF) is a device that traps the soot and unburnt fuel from diesel combustion.   You may have noticed if you have one the 07+ diesel pickups that it never puts out any black smoke at all.  The DPF will capture 90% or better of all harmful diesel emissions.   Once the DPF has become "full" of soot, it will need to have a regeneration cycle in order to burn all the soot out.  You may have noticed a light on your dash from time to time that alerts you that the DPF is in "regen" or "cleaning filter."  Basically what is happening during this process is that the engine's computer has decided from the information that it receives from the sensors installed in the exhaust that the DPF has filled up past it's acceptable limit.  The computer then opens the EGR (exhaust recirulation valve) introducing hot exhaust into the intake to help get get exhaust gas temps higher and also injects a small shot of fuel into the cylinders when the exhaust valves are open.  The raised exhaust temps and the small amount of fuel then burn out the particulate (soot) that the DPF has collected since it's last regen.  Once the computer gets readings from the sensors in the exhaust that the filter is flowing an acceptable limit again, it ends the regen cycle.    The frequency of this cleaning cycle is different from vehicle to vehicle  depending on use, mileage, and engine condition.  

Myths about the DPF system:

1. The lines on the side of the exhaust are fuel lines that dump fuel directly into the filter and the other connections are glow or spark plugs that ignite the fuel to clean the filter.

Not at all.  As I stated above,  the fuel needed for cleaning the dpf is entered into the engine cylinders by route of the regular fuel injectors during the exhaust stroke of the engine.  A small shot of fuel is pushed out with the rest of the exhaust gas.  The metal lines everyone sees on the side of the DPF filter are for a pressure sensor that is usually attached to the side of the transmission or frame.  They have the long metal tubes on them to get the temperature of the exhaust they are measuring down before it reaches the sensor.  Again, I don't care what the tech at the dealership says about those lines, if he says they are fuel lines (which I hear all the time), he is an idiot and you should remove your truck from there as quickly as possible.  The other wires you see going to the exhaust before and after the DPF filter are not spark or glow plugs.   They are thermocouples that measure exhaust temperature.  The computer uses exhaust temperature and pressure before, at, and after the dpf to measure how plugged the dpf is and when it's time to perform a regen.

2. I can just remove the DPF filter and put a piece of pipe in there.

Sorry, no.  If you remove the DPF filter and make no adjustments to the engine's computer, it will enter either a limp mode or a constant state of regen.  Simply put, all the sensors and the dpf have to be in perfect working order when running the stock vehicle's programming or else your truck will go haywire and you will not be able to drive it.

Common problems with the DPF system:

1. Poor Fuel economy - This is the number one complaint we get from customers who have trucks equipped with a DPF.  Most customers who traded in their pre-07 diesel pickups have been completely unhappy with the lack of fuel mileage that used to enjoy.  The average fuel economy we hear people report on the DPF equipped trucks is usually 12-14 mpg.  Many of these folks traded in trucks that did 18-22 mpg and are completely disgusted. 

2.  Excessive regens - Many of our customers who use their trucks for work complain about very frequent regens that kill their fuel mileage and performance.  Many customers who work outdoors in the winter were used to leaving their old diesels run all day while they were on the job site.  The DPF equipped trucks don't handle this very well.  The cooler idling temperature of the exhaust gas will soot up the DPF on an accelerated rate.  It is not uncommon for these customers to be on their second or third filter change because the truck went into constant limp mode.  The usually dealership response is: "You can't let these new trucks idle."  Which goes over pretty well with guys who are stuck at a job site five miles back in the woods all day and the temperature never gets above ten degrees.

3.  High replacement cost - If any of you have had to pay for a DPF replacement out of warranty, you probably had a heart attack when you got the bill.  A replacement DPF (which isn't available aftermarket yet) runs roughly $2000-$2600 for the just the filter alone.  And hears the scary part.  DPF life is estimated between 120,000 and 150,000 miles.  If you plan on keeping your new diesel pickup for a few hundred thousand miles better start a DPF fund. 

4.  Restricts performance modifications - With the new diesel pickups, the potential for horsepower improvements is tremendous.  We have taken all three brands of pickups to close to or over 500 rear wheel horsepower and 1000 ft/lbs of torque with just intake, exhaust, and programming modifications.  Never has so much performance been so easy and affordable while still maintaining street manners.  The only problem is anything past a small tow type tune will aggravate the particulate filter.  Turning up the engine will produce more soot which will plug the dpf sooner causing more regens.  Many customers who run a 100 horsepower program report very poor fuel mileage and constant regens. 

What can be done to extend DPF life and limit regens?:

Since we are not allowed by law to remove the DPF system, we are stuck with it if you want to comply with Federal emissions and keep your truck legal.  Here are a few tips to help mileage and DPF life:

1. Use the right fuel - It is absolutely crucial and necessary to use ultra low sulphur fuel in any vehicle equipped with a particulate filter.  High amounts of sulfur in the fuel will plug the DPF immediately.  We get lots of questions from farmers about the red fuel.  As far as we know you can't buy high sulfur fuel commercially anymore.  We have a refinery roughly ten minutes from the shop that refines diesel.  Both fuels are exactly the same, their is just red dye added to the offroad fuel.  It won't hurt anything to run the low sulphur red fuel.  The other question we get asked is about additives.  Our advice is to only run products that were made for diesel fuel.  Power Service, K100, Standyne, and Flash Lube for example are brands that we see no problems running.  DO NOT add any sort of homemade fixes.  Adding a quart of saw oil, atf, or anything else probably isn't a good idea.  It will burn dirty and may clog the dpf.

2. Use the proper engine oil - Make sure you are using an engine oil that is rated properly for your truck.  Some engine oil gets burnt up in combustion no matter what.  If you are running oil that is not formulated for a DPF equipped vehicle, it will soot up the filter sooner.

3.  Keep idling to a minimum - Simply put, idling contributes to dpf problems.  Period.  Keeping the rpm's elevated during will help.  Keeping idling to a minimum is best for these trucks.

4.  Run it hard once in a while -  Don't be afraid once in a while when going up a hill to matt the throttle for a few seconds.  Running the truck hard and getting things nice and warm will help clear out soot deposits.

I want to remove the DPF.  What can I do and what will be the benefits?

First thing, it is absolutely against the law to remove or disable any emissions device for any vehicle that is going to be operated on the public highways.  If you decide you want to remove emissions equipment for any reason, it is solely up to you and your mechanic to decide what is safe and legal for your application.  I do not condone nor advise removing the dpf or any other emissions device.  All the examples I speak about below were tested off-road and the mileage tests were performed on our Superflow chassis dyno that simulate the load the truck has alone and when towing.

We have done some testing on all three brands of trucks to see what results could be achieved by removing the dpf filter system.  There are many products available for off-road and competition use that will disable the dpf system.   You have to run some sort of aftermarket device to disable the system or there will be problems when you remove the DPF.   There are several options that will allow the removal of the DPF without any horsepower increase and also several options that will add up to 250 horsepower along with removing the DPF.

Here are the test trucks we have done controlled tests on our chassis dyno with:

Truck #1:  2008 Ford F-350 6.4 Powerstroke

Mods:H&S MiniMaxx, S&B Cold Air Intake, DPF/CAT Delete Pipe
Stock RWHP: 285
After Mods RWHP:       556
Average Mileage stock: 11.8 mpg
Average Mileage mods: 18.4 mpg

Notes:  Very basic delete package.  Overall mileage jumped 5.6 mpg on simulated highway driving.  Horsepower levels range from 40HP increase to 185 hp increase on the EDGE Race Evolution.   Stock air box would pull filter restriction gauge with clean factory filter on even lower levels.  Air box upgrade a must for this package.

Truck #2:  2008 Dodge 3500 6.7 Cummins

Mods: Full 4" DPF and Cat delete exhaust, Flo-Pro DPF electronics package
Stock RWHP:  294
Mod RWHP:    311
Average Mileage Stock:   12.1 mpg
Average Mileage Mods:   18.9 mpg

Notes:  We were really impressed with this package.  The Flo-Pro electronics only disable the DPF system and add absolutely no horsepower.  The free flowing exhaust showed some horsepower gains.  Mileage test was simulated highway driving with a truck weight of 8700lbs.  Great mileage gain of 6.8 over stock.  Inexpensive delete package for off-road work trucks.

Truck #3:  2008 F-550 6.4 Powerstroke

Mods: DPF delete into dual 5" exhaust, S&B Cold Air Intake, Power Hungry Performance Gryphon programmer
Stock RWHP: 268
Mod RWHP:   447
Avg HWY Mileage Stock: 9.2 mpg
Avg HWY Mileage Mods: 17.3 mpg
Avg TOW mileage Stock: 6.4 mpg
Avg TOW mileage Mods: 14.2 mpg

Notes: This is a package that we put together to simulate the gains possible on one of the hard working trucks that tows alot.  The horsepower increase was dramatic, but the mileage gains were tremendous.  We simulated a truck weight of 11,500 lbs for the highway tests and a trailer weight of 12,000 lbs for the tow test.  The highway mileage tests of the mods showed a 8.1 mpg gain while the towing test also showed an amazing 8 mpg gain. 

Truck #4:  2009 Dodge 2500 Cummins 6.7

Mods: 5" straight DPF/Cat delete exhaust, S&B Cold Air Intake, H&S XRT programmer

Avg HWY mileage stock:14.6 mpg
Avg HWY mileage mods:21.2 mpg

Notes:  We only did simulated hwy mileage tests on this truck.  We just used the XRT programmer to remove the DPF functions from the computer and left the horsepower stock.  The XRT has horsepower increase levels of 60, 120, 175 horsepower.  It will also shut the egr system off as well. 

Truck #5: 2008 Ford F-350 6.4 Powerstroke

Mods: 4" DPF delete pipe, 5" MBRP dpf back exhaust, S&B cold air intake, Innovative Diesel custom tuned SCT Livewire

Stock RWHP:289
Mod RWHP:  536
Stock MPG:   11.6 mpg
Mod MPG:     17.4 mpg

Notes:  This truck was an animal!  The custom tunes were some of the smoothest shifting of any of the options we have tried and the power was crazy.  There was a 247 rear wheel horsepower increase over stock on the highest level and the rear wheel torque was over 1000 ft/lbs!   You would think there would be a serious drop in the mileage department, but we were surprised to see the truck gain nearly 6 mpg at even this horsepower level. 


In conclusion, if you are looking for some serious horsepower for the drag strip or the pulling track, these new common rail diesels make serious horsepower with very little modification once the dpf is out of the way.  Also, if you only operated your truck off-road there are some extremely impressive fuel economy gains to be had by removing the dpf filter.  It is really too bad that we couldn't run the trucks on public roads with the dpf removed.  We truly would have incredibly powerful trucks that get great mileage and have wonderful street manners. 

Thanks for reading,
John Anderson
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