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Message: <blockquote data-quote="Rizzo" data-source="post: 378222" data-attributes="member: 736">Ok, I will lay it all out so try to follow along. This applies to engines equipped with SCR or as you refer to them as DEF equipped.Selective Catalytic Reduction=SCRDiesel Particulate Filter= DPFExhaust Gas Recirculation= EGR(this is the biggest killer of fuel mileage)Diesel Exhaust Fluid= DEF Nitrogen Oxides= NOxEngine Control Module= ECMWhen the engine is started it does a system check for the turbo vanes to ensure it has full range of motion to control boost pressure, exhaust pressure, exhaust temperature and turbo speed. Then it does a check of the intake throttle valve(yes they have them now) to make sure it can open and close to manipulate intake temperatures. Then it does a check of the EGR system to make sure the valve opens and closes and the pressures are correct. All the while it's monitoring the temperatures and pressures in the aftertreatment (DPF and SCR catalyst). It is also monitoring the NOx at the outlet of the turbo. Now your in the engine and aftertreatment warmup cycle. This window is where the EGR system is active and the exhaust recirculation valve is allowing exhaust gas to be introduced into the intake stream and burned in the cylinder for NOx reduction since the SCR system is not active which can be due to DEF temp or SCR cat temp or both. Now a short time later let's say as you drive out of your neighborhood and begin your trip. The SCR system will become active and begin using DEF for NOx reduction and the EGR system becomes mostly inactive until extended idle or very low load conditions occur. The SCR NOx outlet sensor is now being used with the engine NOx outlet sensor and the ECM compares them to make sure NOx destruction is sufficient inside of the SCR catalyst. How the process happens is DEF is injected after the DPF into the exhaust stream as it enters the SCR catalyst where a chemical reaction between the DEF and the metals in the catalyst and turns the NOx into nitrogen and water. While all of that is going on the DPF has been doing its thing collecting what little bit of not just soot but ash that has been coming out in the exhaust stream. To clear something up with DPF and exhaust temperatures. The engine is able to get temperatures up to 700*f at idle if need be to get things warmed up as fast as possible. How does it do that you might ask. It will change retard fuel injection timing which causes more of the heat to exit into the exhaust stream instead of into the piston. The throttle valve will be partially closed along with the turbo vanes. Now for regeneration cycles, the engine is in a passive regeneration cycle quite often meaning its able to keep the DPF differential pressure (the inlet and outlet) in check so the dreaded active regeneration cycle isn't needed. They will however need to complete one every so often just to thoroughly "clean the pipes" and make sure the whole system is able to perform the process.(It's programmed into the ECM as a health check. It's not common for this condition to occur but I have seen it a few times). The DPF has to reach a temperature of 1040*f to complete the regeneration or cleaning process and the time is determined by the differential pressure or whatever the engineer that wrote the tuning. How it gets to that temperature differentiates between manufacturers but it needs diesel fuel introduced into the exhaust stream and as it hits the DPF it reacts and burns and inturn cleans. There is so much that goes into how all of it works together and a lot of different variables as to what happens when. So this is just basic function. So in terms of "Deleting" and adding HP. The biggest benefit comes from either removal, blocking, or disabling the EGR system. This is the biggest killer of fuel economy. Removing the aftertreatment system helps with the small amount of fuel used during active regeneration, which is pretty minimal. Emissions intact tuning is very common and they are able to disable the EGR function with no adverse effects to the aftertreatment system other than a small increase in DEF usage. Now adding horsepower while increasing economy is entirely possible. Most "tow" tunes the base change is injection timing which uses no more fuel it just increases pressure in the cylinder which makes more power with the same or less fuel. This is a big deep dark hole and I dont have enough time in the day to go into all of the fine details but hopefully this helps.</blockquote>

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