2007 GMC Sierra 5.3 with AFM getting bad milage

[Justin07gmcsierra]

My 07 Sierra 5.3AFM is getting terrible milage I hear of people getting around 20mpg and I can only dream of that my truck has 220k and still runs like it has 50k but it's getting terrible fuel milage anyone have any suggestions to what my problem might be? Thanks

[2017SierraSLT]

I would start with replacing the upstream oxygen sensors with OEM units if they have over 50k miles on them. The Bosch replacements will be worse than the originals. Check to make sure that your oil, spark plugs, and air filter are fresh. My '13 with 9800 miles with a Diablosport 93 octane canned tune easily pulls 21 MPG on the highway, and over 16 avg. I run full synthetic oils, the Airaid MIT, K&N drop in filter in the OEM box. If you have larger than stock tires/wheels, you will be hard pressed to get great mileage. Extra unsprung weight kills mileage.

[Justin07gmcsierra]

It's not the oil, plugs, or air filter, but I will replace those o2 sensors, I'm also going to replace the Mass airflow sensor and intake manifold gaskets this weekend and see if that helps, I do have aftermarket wheels but they are the same size as stock and tires are only slightly larger than factory, I appreciate your input, I'm definitely going to look into replacing the o2 sensors, everyone I ask that I know just thinks the poor fuel miles is an attribute to my high miles, but as I said my truck runs perfectly no misses, good compression, and it does not use oil so that leads me to believe it has to be something else Im gonna try replacing the few things I mentioned and see if my milage improves

[2017SierraSLT]

I would try cleaning the MAF sensor before replacing it. All of the major parts stores sell spray MAF sensor cleaner that will effectively clean the sensor and not damage it.

[Colossus]

At 220k, I'm betting your catiletic (I probably spelld that wrong) converter is toast. Get that check and replaced first before doing the 02 sensors. The onboard computer and the O2 sensors on a 2007 are fairly advanced enough that if they were the root cause of a very noticable reduction of fuel economy, they'd likely be setting a code. What kind of fuel economy are you getting? Is it stock or what modifications have you made to it? We need more info.

[RyanbabZ71]

Define terrible milage? What are you getting. Were you getting a good mpg and it has gotten worse?

 

What are your driving habits? Fuel type?

 

 

 

 

Ryan

[Justin07gmcsierra]

At 220k, I'm betting your catiletic (I probably spelld that wrong) converter is toast. Get that check and replaced first before doing the 02 sensors. The onboard computer and the O2 sensors on a 2007 are fairly advanced enough that if they were the root cause of a very noticable reduction of fuel economy, they'd likely be setting a code. What kind of fuel economy are you getting? Is it stock or what modifications have you made to it? We need more info.

[Justin07gmcsierra]

Catylitic converters do not just go bad, something causes them to go bad (burning oil) and although my truck has high miles it doesn't use a drop, my truck is bone stock no mods, I'm getting like 10-12 mpg and I am in the car business and I drive other trucks that have the same trim and they get better milage

[RyanbabZ71]

Cats can go bad. They are made of metal and will eventually degrade. My dad just had to replace his on his 2000 blazer with about 135K miles. Basically the environment killed them

 

 

Ryan

[Bad Bowtie2]

What is the history of your spark plugs & coil wires?

 

Had your front end alignment checked lately??

 

Any add-on mods?