Improving mileage in a diesel enging


I’ve heard a lot of guys brag about putting “chips” in their computers and/or installing different after market air intake or exhaust systems to improve fuel mileage. Does this really work and is this harmful to the engine to monkey with the manufacturer’s design like that?

The economic down turn has cost me my job and I’m thinking about using my '04,6.5TD Duramax diesel to run hotshot to make ends meet.


How much you might gain if anything depends on the specific car. Some models are good subjects for the mod. On the other hand it is possible that you might just loose some reliability or life to you car. All such changes have good points and bad. The manufacturers have the people and money to try out many variations and they put what they feel is the best ccompromise in there cars. Diesels are a little different since most in the US are European models and Europe has different (generally more restrictive than ours) pollution requirements so you may get chips optimized to meet their pollution requirements.

If the only difference is in pollution output, you likely will never find out.


I’m not sure I follow. My vehicle is a 1 ton dually with a Duramax diesel engine. Your reference to cars, does that include pick up trucks, such that the duremax may also be a European model? Also, are you saying that depending on the engine, the only change may be to change the pollution output with no corresponding improvement in power output or fuel saving?


I don’t get into this area much at all but I do know that the diesels are very receptive to airflow changes and programming. This is tailored to meet your driving habits (low end towing, economy, all out power, etc.), so I would say that a significant difference could be noticed with some modifications. The gas engines gain little but the diesels can really be perked up.

I’ve seen a few guys running diesel pickups at the dragstrip after a few mods and programming and to be honest, one of them was jaw dropping.
A Ford King Cab dually diesel with a tool box in the back, A/C on, and running almost 12 flat in the quarter mile astounded me. The only one more astounded was the poor sap (test and tune night) who raced this guy with a turbocharged and modded Subaru WRX twice and got his head handed to him both times by the diesel.
In both races, it was over by the 300 foot mark.


depending on which ‘channel’ you are in…

i would think it also depends on how heavy the load is going to be. you mention hotshoting… i take it to mean doing special delivery of odd ball shipments? then the weight issue is moot, and you need to maximize mpg.

i would think the rear end gear ratio, and your personal driving habits would effect the longevity, MPG you would desire to use this for deliveries.


Making engines more powerful doesn’t necessarily make them more fuel efficient. Unmodified diesels already are fuel efficient because that is one of the main design criteria of industrial engines. Unless the efficiency has to be compromised somehow to meet emission standards and you are willing to pollute more, it’s best left alone. Just make sure that what you do is reversable lest annual smog testing comes to your area.


If you want guaranteed better fuel mileage and don’t have a regular need to haul things, trade the big diesel for a compact gasoline car with a manual transmission and go from 20 mpg to 35 mpg highway. A cheap $250 trailer kit will cover your hauling needs. People who chip a diesel are going for more power, not more mileage.


I’m not equating power to economy; only pointing out that diesels are easily tweaked and gains can be made in the area desired.

One can even take a gasoline engine, modify it a lot, and still meet any emissions standards.


Channel Cat,

I owned a 2004 Chevy Duramax HD 2500 and I used an “Edge” adjustable “chip set.”

It does NOT incrase fuel economy. It does address some issues related to fuel curve on the injectors and Allison transmission shift patterns.

If you’re considering hostshot loads, invest in a cold-air kit for the engine - Chevy has a retrofit-- that will prevent overheating on heavy loads.

That is the most serious issue with this model/make truck-- overheating on max load. (That’s why I ended up selling mine.)




Been out of town and just logged back in. I am interested in mpg as this will affect my bottom line. I am also concerned about maintenance cost and want to avoid overheating as Matt pointed out.

Matt, what are the fuel curve issues? Where can I find the cold air kit and do you suggest I do both, the chip to deal with the fuel curve issues and the cold air kit?

BTW Cappy, “Channel Cat” was my CB handle from years ago. It’s play on a type of catfish( I’m an avid fisherman) and the channels of a CB.


When diesel engines are designed, there’s a safety margine programmed into the engine management system so that engine isn’t pushed to it’s absolute limits causing damage. These reprogrammers take the operating paramiters of the engine management system into this safety margin. So basically, you’re operating the engine on the hairy edge.

When bumping up the performance on a diesel engine, you have to take into consideration if the transmission is up to the task of the extra torque introduced. The transmission in your vehicle is built by Allison per GM specs. And is in no way a REAL Allison transmission in it’s design. So you have to go into the transmission and make upgrades if you’re going to run on the hairy edge. Otherwise the tranny might not be able to handle it.

Installing any of these aftermarket systems can increase the performance out of a diesel. But it’s horsepower and torque that are sought after. And anytime you want more performance, it requires more fuel.



Channel Cat,

Sorry, I’ve been off the board for a while.

The edge unit adds more fuel = power.

GM has a cold air kit “fix” that re-routes the cold air duct from behind the radiator to inside the passenger fender area (with water dam).

Yes, the chips (including the Edge) will provide more power, but not better fuel economy.



Add up what it’d cost for the chip, CAI, etc and consider how much fuel that money can purchase