AFM Problem

nashss · April 17, 2012

alright so I have a gmt900 silverado 5.3 CCSB 2wd with 105k miles and when I first bought it last fall I was averaging around 18ish which I thought was pretty good. The only thing I have done is add a drop in KN Filter and a 14" Magnaflow muffler and just today I went and filled up and checked my mileage and came up about 13.5 and this was done by calculator not DIC on the truck. WTF really???? My 03 SS with the 6.0 v8 AWD with sprited driving did that. This is really making me hate the AFM because I don't feel its doing a damn thing. I want my SS back this system is crap and I miss the power of my SS

SouthCo · April 17, 2012

That's a big drop in mpg. Maybe something besides the afm is the culprit. I've got 7k miles on mine and I wish I could get close to 18mpg.

00Silverado4x4 · May 29, 2012

Wondering if there is an update? Did you find out why the drastic drop in fuel mileage?

nashss · May 29, 2012

no updates. my solution is get something that makes me feel better about getting this kinda mileage. 6.2 or 6.0 is gonna be my next truc;

SouthCo · May 30, 2012

I don't hand calculate mileage. I can only tell you what my DIC says. I have an overall average of 15.8mpg. I just turned 9k miles. I tow a little and don't floor it like crazy but do step on it from time to time. I can't complain about the mileage I'm getting. My 2003 Tacoma with a v6, that I sold, didn't do a whole lot better.

nbscanuck · May 30, 2012

When was the fuel filter change last? Ever clean the MAF? Was that with winter fuel or summer fuel? Temp and humidity effect MPG. If you floor it a few times one tank and not the next, makes a big difference. Lots of variables.

elcamino · May 30, 2012

Those that add louder exhaust and high performance air filters tend to drive more aggessively once they do, weather they will admit it or not is another story. Why else add those things then? Contrary to urban myth they do not improve mileage, they can have the opposite effect though because the driver now enjoys the noise they make and drives to effect that end.

TimmyG · May 30, 2012

Also could of been crappy gas, you have to check more then one tank to get a good avg

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marksoldtowne · July 2, 2013

Hi,06sierraZ71

Drastic drop in fuel mileage occur when there is no change in driving habits.There are some reasons for a drop in gas mileage, includng but not limited to overdue maintenance, low tire pressure, a failing sensor , low fuel pressure, change in weather, and even a dragging brake.The pump uses the gas to keep itself cool. Also noticed a strong smell of fuel from the exhaust.

BlackZ71Silverado · October 16, 2013

It doesn't really seem like you have an AFM problem. The problem may be the aftermarket parts you added to your truck. That K&N filter will change the AFR and that may be what is going on.

You are going to have to run a log and see what your numbers look like. I am willing to bet with the exhaust and K&N it's off quite a bit. It's also possible that you MAF got some filter oul on it, that would cause issue as well.

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Daryl Z71 · October 16, 2013

When was the fuel filter change last? Ever clean the MAF? Was that with winter fuel or summer fuel? Temp and humidity effect MPG. If you floor it a few times one tank and not the next, makes a big difference. Lots of variables.

Fuel filter is a non serviceable part. It's in the tank.