06 sierra mpg plummeted within a day?

[Firefighter7]

I have recent taken close to a 150 mile trip and my mpg was normal for my truck at 18 mpg. I was on vacation and went to take my truck down the road and noticed my fuel economy was around 4-7 mpg and it goes back to normal when I really put my foot down and get back off of it, it goes back to normal. After a while my mpg will start to drop back down if I slow down to a stop. I have no idea what is causing this and no dtcs are being detected.

 

Mods

Bully dog triple gt programmer

K&n cold air intake

Straights with a Y dueled out the back

[GasHog369]

Sure you didn't accidentally reset it and its jut relearning now? I did that before on my old truck when it was on steering wheel. It showed same as your mentioning.

[Firefighter7]

 

Sure you didn't accidentally reset it and its jut relearning now? I did that before on my old truck when it was on steering wheel. It showed same as your mentioning.

[Firefighter7]

I am sure I am watching my programmers instant mpg and I am also watching the vehicles display and they are both considerably low for the rpm range that I am running.

[pm26]

Deprogram the truck

[elite0259]

It might not be programmed, I have the same tuner he has, stock tune. I just use it as gauges at this point.

[Firefighter7]

I returned it to stock with no programmer today and it still said I was sucking down fuel. I'm gonna drive home tomorrow with the programmer on and monitor air flow, fuel flow, load, and timing.

[Firefighter7]

06 gmc sierra 1500 2wd with the 4l60e tranny and 3.23 rearend and bully dog programmer on the performance towing shift patterns

[r1byker]

I guess checking it manually would be the way to go. Fill it up, drive a hundred miles or so, and fill it up again. If the figure matches your DIC, then you know the DIC is right and something's wrong under the hood. If your DIC doesn't coincide with what your manual calculations, then you know it's the computer.

[TimmyG]

I would start by cleaning the mass air flow sensor/thottlebody and I would unplug the battery for 1/2 hour or so

 

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[Gurrzt]

I would start by cleaning the mass air flow sensor/thottlebody

 

Sent from my SCH-I535 using Tapatalk 2

+1 on that, how is it idiling? check your wires and your plugs.

[Firefighter7]

Idles perfect runs smooth throughout the entire powerband! I am going to clean the air filter when I get home as in I do not have the stuff with me to do it properly.

[Duelin]

What did you get for mileage when you divided the gallons used into the miles traveled?

[Firefighter7]

Well I made it home yesterday and my gas mileage ended up at 18.3. So I know my cruising mpg is fine and the computer is accurate. I am cleaning the air filter as we speak so hopefully that will fix the problem. The MAF filter is clean but the airfilter wasn't at all. I am thinking airfilter because when ok not demanding much and the mpg is fine but when it starts sucking a lot of air the mpg goes down to 0-3

[Bad Bowtie2]

If you truck has the steering wheel controls & the DIC, maybe someone switched your MPG settings to "instant MPG" instead of the "average MPG"??

 

Or maybe, if you just bought gasoline, got a bad tank?? (Sea Foam fuel treament time)