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Fuel efficiency question

sab8s418

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I’ve got a 2021 6.2L. I swapped out the stock muffler for a flowmaster super 50 and also got rid of the flapper valve. I also installed the cold air inductions cold air intake. I am getting less than 13 mpg now compared to almost 16 mpg before. Any ideas what the problem could be? I am not the most mechanically inclined when it comes to vehicles. But I was expecting an increase in mpg rather than a decrease.
 
It's a 6.2, they don't get good mileage no matter what. My best ever was 20mpg. Usually I'm around 15mpg mixed driving. City driving kills MPG in the 6.2 unless you're super light on the gas pedal. I have a Magnaflow muffler delete with the flapper removed. I added an AEM dry flow stock replacement filter, neither added any MPG. I added a K&N that just replaces the tube from the stock box to the throttle body. It added nothing in MPG.
 
I’ve got a 2021 6.2L. I swapped out the stock muffler for a flowmaster super 50 and also got rid of the flapper valve. I also installed the cold air inductions cold air intake. I am getting less than 13 mpg now compared to almost 16 mpg before. Any ideas what the problem could be? I am not the most mechanically inclined when it comes to vehicles. But I was expecting an increase in mpg rather than a decrease.
over how many miles did you average 16?

My guess is that either 16 was either higher because of an out of the ordinary trip or that if you're now at 13, you're more inclined to get on the throttle harder to hear the results of your labor. Don't discount that as an option, because even if you aren't TRYING to do it, that's the whole reason you swapped the muffler in the first place.

Im at about 15MPG on a normal commute on a 21 6.2. S&B CAI and a new muffler arriving this weekend, I would anticipate that drops once the muffler goes in.
 
over how many miles did you average 16?

My guess is that either 16 was either higher because of an out of the ordinary trip or that if you're now at 13, you're more inclined to get on the throttle harder to hear the results of your labor. Don't discount that as an option, because even if you aren't TRYING to do it, that's the whole reason you swapped the muffler in the first place.

Im at about 15MPG on a normal commute on a 21 6.2. S&B CAI and a new muffler arriving this weekend, I would anticipate that drops once the muffler goes in.
I bought the truck with 8k miles. Average over those was 15.8. I put 2k on it stock and the average over that was around 15. I’ve probably put close to 1k on it since CAI and muffler and average is 13.2. I do hardly ever drive on the expressway and almost all my driving is backroads and city driving so that’s definitely a factor. Just seemed like a bit of a drastic drop.
 
I bought the truck with 8k miles. Average over those was 15.8. I put 2k on it stock and the average over that was around 15. I’ve probably put close to 1k on it since CAI and muffler and average is 13.2. I do hardly ever drive on the expressway and almost all my driving is backroads and city driving so that’s definitely a factor. Just seemed like a bit of a drastic drop.
I heard that if you don't disable AFM or DFM, then the flapper valve actually helps with highway mileage. But if you disable it, then deleting the flapper valve will help with highway mileage (even though deactivating AFM or DFM will lower your highway mileage otherwise). I did aftermarket exhaust and disabled DFM at the same time, so I can't say how mine was affected.
 
My 20mpg trip which is the entire tank of gas, not some random grab for a few miles, was driving at 63mph on a 2 lane road with the AC on. My muffler was deleted then. I chopped it and the flapper off the 3rd day I owned it.
 
After I installed the same intake, I too lost mpg. It happens. The only way to get max benefits is to have the ecm retuned to account for more air flow. I started running higher octane gas and my mileage increased to better than it was before adding the intake.
 
I've always run premium in my truck. I found when I was in Iowa traveling back home a station that had pure gas with no ethanol that I think was 92 octane got me about 1mpg better coming home to Michigan, but it could have been a tail wind too. LOL
 

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