June 8, 2011
Horrible gas mileage, with K&N and Magnaflow?????
Every truck I ever owned in the past, the first thing I always did was upgrade the air filter and the exhaust to give it “more power” and “better fuel economy.” I had a ’97 Dodge Ram with the 5.2L motor. I was getting probably 12-16 in town and about 18 on the highway. When I put a K&N and exhaust on it, I was getting 11 everywhere. So when I sold it and got my ’05 F-150, I figured I would go all out. I got the $700 magnaflow exhaust system, and a full gen-2 K&N intake. I was getting 14-18 in town, and 18-20 on the h ighway. After my “fuel saving parts” I’m getting 10-12 in town, and 13-14 on the highway. What’s the deal???
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Filed under Gas Conservation FAQ by on Jun 8th, 2011. Comment. 
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Comments on Horrible gas mileage, with K&N and Magnaflow?????
After your upgrades, did you reset the ECU/ECM?
Without checking the components (on board computer) it’s difficult to say exactly what your problem could be.
A quick stab in the dark though, would lead me to think that the changes you have made, has affected the air flow sensors.
Late model engines work like a PC, any change you make in one component, effects the overall performance of the entire system. For good or bad.
What you have done by increasing the overall airflow of the “system”, you have changed the factory set specs for the remaining components that where not modified.
u will have to get a performance upgraded pcm bacause factory pcm is calibrated for stock exhaust and mass air flow sensor,etc.Now u have more air flow at engine which mean that means more fuel is needed to function somewhat correctly which leads to more fuel consumption.Factory pcm may not can perform actions needed for better economy.
your using your right foot more to hear the sound of the new equipment
OBD II
It doesn’t play well with aftermarket exhaust and intake mods.
I am really surprised that you do not have a “Check Engine” light on all the time.
One has to shop very carefully for parts when dealing with these vehicles and only get them from places that certify their compatibility.
Yours is not an uncommon tale of woe.
ASE Cert Auto tech 30 years, VW Tuner since 1978
Dodge has always had issues with fuel economy…
Ford engineers have designed these vehicles for air flow and all already, and unless you modify the PCM for this additional air flow, that’s why you are pissing in the wind for dude… Tuners will tell you, that when you start going with bigger air intakes, it can effect alot of stuff without the programming to solve it.
Actually what it does, is it introduces more air, which the system tries and adds more fuel to compensate.. hince you loose the fuel economy.. if you forgot to oil it or over oiled the filter, it can cause you nightmares too….
skip the gen 2 k&N, go back factory with a regular paper filter and I find this will probably be your better bet…
But you’ve learned what others are learning .. the factory is getting better at power and fuel economy.
Actually if you are keeping your foot out of the throttle and getting that bad of milage take your mass air flow sensor out and look at it. Sometimes when you accelerate the oil from the air filter will suck up through the air intake and stick to your mass air flow sensor. It happened to me on my Mustang and I clean my mass air and took care of the problem along with giving me some more throttle response.
on any vehicle where you change something to get more power you will always lose fuel mileage. So all I can say is that for what you are losing in mil age I hope you are making up for in noticeable power.