I have a 2005 Dodge 2500 extended cab 4x4 with 5.9 in it. I put a K&N air intake on it and the fuel mileage went way down. I was getting 17-18mpg on the freeway and it dropped to 10-13mpg. I asked one diesel mechanic and he said that it has to do with the computer registering more air coming in, so it dumps more fuel to match it. Does this problem and diagnosis make sense? My ultimate goal is to get fuel economy up, not down. Someone suggested a computer reprogrammer. Does anyone know which one works best for improved fuel economy on my truck?

 

First of all welcome to the forum, Do you have any other mods on the truck? I recently put the same intake on my truck. Are you hand calculating the mpg's or is the over head reading different?

 

The only other thing I have on my truck is an oversized set of tires and a leveling kit. But they were put on before the intake. The mechanic said that the computer trys to maintain emissions standards so that is why it dumps more fuel. There is a performance difference with the intake, but the mileage sucks! Any thoughts?

 

How many tanks of fuel have you gone through since intalling the intake?

There is usually a slight drop on the first few tanks because guys tend to romp on the skinny pedal whenever they get a new part, especially one that lets you hear the turbo, and subsequently your mileage goes to crap.

Now, going from 17 - 18 down to 10 - 13 is little drastic and is WAY more than an air intake is going to cause.

 

Are you supposed to disconnect the computer so it resets to the new air flow coming in with the new filter? just a thought.

 

No, the Cummins doesn't have a Mass Airflow Sensor like a gasser does.

The only thing it sees is the Air Intake Temp and the Manifold Absolute Pressure.

The ONLY thing that intake is gonna do is eliminate some restriction in the intake track and allow the turbo to spool a bit faster.

The only negative effect this "could" have on fuel mileage would be that the more air the ECM sees available (i.e. boost), the more fuel it can add.

 

The drop in fuel mileage is city driving or highway with cruise on, makes no difference. I have had probably 15 tanks of fuel through it since intake was installed.

So the ECM sees more air so it adds more fuel, correct?

The dodge mechanic said the only way to correct it is either put the factory intake back on, which he recommended, or use a reprogramer, which he said not to do because it voids warranty. The other thing he suggested was to put high flow exhaust on it.

So if the problem can be corrected with a reprogramer, than which one is the best for my truck? Has anyone seen the results for fuel mileage gains with one brand or another? The added horse power isn't a big issue for me, but the gain in fuel mileage is.

 

Honestly, I dont think that you would see a big improvement in your fuel economy. No doubt with a programmer you can get addicted to the throttle very quickly, but hey give it a shot. Their are many different ones out there. I run a Bully Dog PMT, and I like it. Not saying its the best one out there, but I have had luck. There are also some bang for your buck programmers too. Good luck...I think if coal train posts again...he will have way more info than I.

 

I only worse milage while driving in town. But my highway mileage is the same to slightly higher. Only about .3 mpg's more. I just set the cruise and forget it.

 

None of the programmers are gonna drastically improve mileage.

The best way to improve mileage on a common rail is bumping the timing up.

If you wanna do that, you want a Smarty.

Most of the MPG claims are horse crap.

Here's where I see my best mileage at and this is running my truck as it sits now. I drive it everyday.

I normally get 16 - 18 in day to day driving and 20 - 21.5 on the highway.

I don't look at speed or RPM so much as I look more at boost and EGT numbers.

Boost and EGT will tell you how hard the engine is working.

I try to keep the boost in the single digits and the EGT's (pre-turbo) under 700*. Doing this gets me good mileage.

If you see higher boost, but the same EGT's, you're spinning the engine too fast and wasting fuel.

If you see higher EGT's but the same boost, you're lugging the engine and wasting fuel.

If you see both numbers higher, you're going too fast and wasting fuel.

my best mileage in town comes when I drive with T/H mode on. My best mileage on the highway, with 3.73 gears is at approx 72 MPH and 2000 RPM's.