3/4-ton Diesel

[edwardsss]

Dave, I didn't mean to put you in a difficult situation by asking that question. I have an '04 305/555 Quad-cab, SB, 4x4 and I'm just looking for all ideas to make this truck get better mpg. So far, the electronics that I've researched will give lots of TQ and HP, but not fuel mileage increases. As for aerodynamics...there's a few suggestions out there but aero-body kits don't appear to be in big demand by RAM owners. I watch Cumminsforums, and others. While there are some wild claims there's no solid, independent, testing behind the claims. Thanks for responding though. -Ed

[Diesel_Dave]

cleenspeed, technically any modification (including re-programming) that would result in increased emissions is considered illegal by the EPA. That being said, I have never heard of any individual being prosecuted for modifying their own vehicle.

Most people don't realize this, but for a modern diesel engine the EPA regs (for nitrogen oxides and particulate matter) are THE single biggest thing that hurts fuel economy. I work in diesel R&D, so I could go on and on about this. For a truck like mine there are 2 big things: the EGR system and the DPF. The DPF is the bigger of ther two. You lose mpg's because of the huge exhaust restriction (several times what it would be otherwise), because of the fuel used to regenerate the filter, and because it prohibits good driving styles (you have to be in lower gears in order to keep your rpm's up, and you can't idle much because the DPF gets cold and will plug up).

[Diesel_Dave]

Ed, you have a 2004 so you have EGR but no DPF. You'll see quite a bit of mpg improvement, but not as much as post-2007 folks.

You're right that most of the programmers and other mods are advertised as producing higher TQ & HP, but, in most cases there's significant mpg improvement as well. They're not advertised that way for two reasons: 1) technically, they're not street legal so the companies advertise them "for off-road use only" 2) many guys do use them to increase TQ & HP. Some of that increase comes from burning more fuel, but a lot of it comes from increased efficiency.

It's complicated, but in simple terms high in-cylinder temps boost thermodynamic efficiency, however, they also lead to more nitrogen oxide (NOx) emissions. The programmers make changes to things like injection timing which results in higher efficiency but also higher NOx levels than what the EPA allows.

For post-2007 trucks getting rid of the DPF & EGR and reprogramming can result in over 30% mpg improvement. And I'm not just throwing those numbers around--that's from data I've collected myself.

[cleanspeed1]

Yeah, I never liked the way most OEMs are doing this, even though it looks like all are using other strategies.

[Diesel_Dave]

Trust me, the OEM's don't like it either but they don't have a choice. If you can't meet the EPA regs, you can't sell them--no matter how efficient they are!

[skyking]

Those are some nice mileage figures Dave. My 96 auto has never seen 20 since I purchased it a year ago. In retrospect I should have been shopping for a manual, but I wanted it to be easier for my wife to drive while towing. She drives a clutch OK but it is a different world when you miss a shift at 17,000 pounds on a hill getting started out.

EDIT: I got 21 on my last tank! I guess I got the teenager back into the box.