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Gas milage went to heck--cant figure out why?

Amra

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Amra Enthusiast

Amra

Posted
Posted

I have a 1500 chevrolet extended cab 4x4 truck with the 5.3 engine. These are my mods.

 

Airaid induction

series 50 suv flowmaster exhaust

waitformeperformance chip

 

I was getting between 17-19.5 mpg on the highway.

I was getting 15.5 in city driving.

 

I got this for the first 5 months.

 

Now i have not traveled so i dont know highway mileage but i am getting only 13.5 mpg in city driving. I am easy on the gas as i can be and have not done anything different that i can think of except 1 thing. I got my first oil change and went with mobile 1 total synthetic oil. Im not sure if that alone would do it. I did for one tank put in Marvel Mystery oil additive to my fuel and I lost 3/4 of a mpg for one full tank of gas which led me to think mabey my oil change was the culprit. And by the way I have had no power loss or anything weird happen and i check every single tank of gas i run thru for milage.

 

Also I did a crankcase relearn but that was about a month before the gas problem was noticed. I did this because of the chip from wait for me caused a problem with my check engine light and i was told to do a crankcase relearn. Im not sure if this could of been the problem.

 

So i went from what i thought was good gas mileage to crap and i cant figure out why. Any suggestions would help--mabey the programming is corrupted or something in the chip or mabey you guys have seen something similar and have and answer.

pm26 Senior Enthusiast

pm26

Posted
Posted

All I can suggest is that you reinstall the original PCM with the factory programming and go from there.

larry arizona Enthusiast

larry arizona

Posted
Posted

I am not sure where you are at but winter blend gas will kill MPG by 2.

 

In Michigan gas stations run it from Roughly November until April.

 

I always can tell when I get my first tank of summer blend and I gain nearly 50-60 miles per tank full.

redvett Senior Enthusiast

redvett

Posted
Posted

I am running a W4M tune and have a 1500 5.3, 3.73 EXT,4x4 with and live in MI and my average city is 17.5. Must be your O2 sensors are gone. BTW i use Mobil 1 in engine and axles other than that and a tonneau its pure OEM.

Amra Enthusiast

Amra

Posted
  • Author
Posted

I didnt think of my 02 sensor. Dont know why it would go to crap but that might be it. Would my check engine light go for that though. Also i read on these forums once that your mass air flow sensor can get dirty and go bad and kill mpg--is that a possibility?

kdm101 Enthusiast

kdm101

Posted
Posted

Is this a 2005 (as I'm assuming from your user information to the left)? If so, I'd doubt the O2 sensors would be going south that soon - unless you have a hell of a lot of mileage already. Unless it fails entirely, they don't set a code as they age, they just get slower to react. I just replaced mine this morning, so we'll see if my MPG goes up.

 

Since you post that you have an Airaid intake, I would look at the MAF as you already were thinking. The filter could have been over oiled, which may now be coating the sensor wires of the MAF. For the cost of a can of electronics cleaner (I got mine at Home Despot in the electrical section) and a few minutes time, you can give yours a blast just before your next fillup. If it doesn't solve the problem, have a dealer check it out for any codes that are set but don't light up the SES indicator. As long as it's under warranty, try to make the most of it.

larry arizona Enthusiast

larry arizona

Posted
Posted

Good point, I use a oil wetted filter and you do need to clean the MAF often. Brake clean and a cotton swab will do it. Clean the Z wire behind the MAF grate. Just cleaning the grate will not do much. Just be gentle on the Z wire with the swab. Does not take much to clean it.

 

I would still be curious if your drop in MPG lines up with winter blend gas in Michigan. When did you notice the big drop in gas mileage. It will also be interesting come mid April if it all of a sudden comes back to the mileage you had before.

 

Do not under estimate the MPG loss of winter gas. You get less BTU's per gallon but you won't get frozen fuel lines.

fossil Enthusiast

fossil

Posted
Posted

On 1996 and newer vehicles, if an O2 sensor gors bad or need repalcement it will throw a code unlike the older ones that need periodic replacement at higher mileage.

I would clean the MAF and re-install the stock air filter, go back to stock PCM programming. As for the exhaust, ensure that it is of the same diameter and spec as the stock system as anything bigger will change the backpressure and cause problems.

Also, do ensure you only use "tier 3" gas, you can check websites for this, Chevron and Shell are among the few who refine to this spec. GM highly recomends that only tier 3 gas be used due to its higher detergent concentrations. Maybe your injectors are getting clogged.

redvett Senior Enthusiast

redvett

Posted
Posted

OBD2 will NOT set a code for lazy O2 sensors which cause poor fuel economy only when they get out of the parameters that the PCM is looking for.

jhm Senior Enthusiast

jhm

Posted
Posted

I have given up on trying to get better mpg. Truck is always serviced, you name it and it's been done maintenance wise. When the gas started going up because of Katrina, I really made an effort to accelerate mildly, try to watch for lights about to change, blah blah. Still I get only 13-15 TOPS!. Ihave realised a full size truck with 4wd is what it is, so now screw it, I drive how I want. It is not worth driving like you are carrying nitroglycerine in the bed for a lousy 1 MPG increase.

redvett Senior Enthusiast

redvett

Posted
Posted
I have given up on trying to get better mpg. Truck is always serviced, you name it and it's been done maintenance wise. When the gas started going up because of Katrina, I really made an effort to accelerate mildly, try to watch for lights about to change, blah blah. Still I get only 13-15 TOPS!. Ihave realised a full size truck with 4wd is what it is, so now screw it, I drive how I want. It is not worth driving like you are carrying nitroglycerine in the bed for a lousy 1 MPG increase.

 

 

 

 

Figure it out 1 mpg at 100000mi just at $2.60 a gallon is almost $1100 and gas is going to get up over $3 probably $3.50 or more this summer thay say. So its quite a savings.

Amra Enthusiast

Amra

Posted
  • Author
Posted

I started to notice the drop in beginning of November. The same time i did my synthetic oil change.

 

Real quick question---is getting to the MAF easy and how would i get to it.

redvett Senior Enthusiast

redvett

Posted
Posted

MAF is right on the outlet of the A/C housing just unscrew the clamps and carefully remove it and clean it with electronic contact cleaner.

the blur Enthusiast

the blur

Posted
Posted

Tier 3 gas???? what is that?

all gas comes from the same distibutor. There are only 1 or 2 distributors in all of NY state. when the tankers roll in, they throw some additives in the tanker, and wha-la, branded gas.

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