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brutal gas mileage

1K views 15 replies 6 participants last post by  dwv tx 
#1 ·
i own a 2004 chevy Z71 w/ 285 75 17 BFG TA KO tires. Everything else is stock. I have had the tires about a year and a half. About 6 months ago my gas mileage went from 17 mpg to 13 real quick. I have checked and changed everything simple such as fuel, oil, plugs and wires, air filter. My tires are running 50 psi. I take off slow and drive about 65 on the highway. is it my or my truck? and helpppp.
 
#4 ·
Its got 47000 miles. If and O2 sensor is bad will it always pull a check engine light? Also, the temp here right now is about 95-100 F. After driving for little while with the AC running full blast when I come to a stop light it stops blowing cold air. It also feels like I am losing power in the hills.
 
#12 ·
i will get different mileage based on what kind of fuel i use. beyond that are you losing any coolant? the reason i ask is that the intake gaskets are almost a common problem in the ls motors. also the ecm will store dtc's and not trip the check engine light. you said you checked the common stuff. did you replace the spark plugs?

the ecm in those pickup learns your driving style and adjusts to it. you can clear the memory from it by unplugging the battery and then turning on the lights. it may or may not make a difference.

btw i thought those trucks were coil on plug?
 
#13 ·
same here on the fuel, i get better mpg w/ shell v-power. no coolant loss, I pulled a few plugs and they were in good shape hardly any fouling. But, the engine has a missfire. I will try to reset the ecm and see if that helps. If not what about plug wires?
 
#14 ·
replace your plugs. make sure you get platinums.

i think the wires are attached to the coils, as in not replaceable. but i am not sure.

also if you are concerned about fuel mileage get a throttle body spacer and a k&n air filter. get the td performance spacer, it's cheap and it doesnt whistle. i used to sell them to my customers that were looking to get a couple extra miles to the gallon. it worked very well. should cost you about 75 bucks for both of them.
 
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