I recently bought a 1997 Chevy 1500 with the 350 engine with throttle body. It uses alot of gas. i thought it was leaking somewhere but i checked it out and its is not. The truck runs really smooth at idle. even at like 700 RPM. and it never cuts out while driving. When i bought the truck i had to replace the fuel pump. when i got the pump out and took out the sending unit i seen someone drilled a hole in the top of the sending unit to run a ground wire straight to the fuel pump. I know my truck has a evac system so i filled the hole around the wire with silicone to seal it. My father has a 200 chevy truck and he gets really good gas mileage. What do you think is wrong where do you think my fuel is going. I dont even notice the pressure from the tank when i loosen the fuel cap. Does the evac system improve fuel economy? Like i said it runs good at idle and while driving just uses alot of fuel. even on the highway with the cruz on. I drove 17 miles and back and it used a 1/4 tank of fuel. Its really starting to irritate me. I just dont understand these new fuel systems. with the vacuum and evac systems. please someone give me some information that will help me out. Thanks! my truck has the vortec engine. and i believe it has the spider injectors to. no fuel lines go to the throtle body its self. i changed the plugs and cap and router today to. i havent driven it to see if it has improved. theses are the codes that come up when the check engine light is on.....

P0430- Catalyst efficiency low bank 2
P0154- H02s21 circuit condition (heated oxygen sensor bank 2 sensor 1)
P1351- Ignition control module (ICM) high input

I cant figure out what these mean. HELP HELP HELP

 

Cat efficiency bank 2 means your second cat is bad (not doing its job of converting exhaust gases)

the second code P0154 means your sensor is not reading correctly (this is sensor 1 bank 2 before the bad cat) this can be the cause of your gas mileage problem, your O2 sensor can be stuck on rich and could be just dumping fuel into your engine.

also what ive done for mileage is clean my fuel system too, i ran seafoam though the vacuum line when the truck was hot and it got alot of carbon off my intake valves which made her run better and surprisingly better mileage. and also once a month i ran premium gas though her for the detergents in the gas and so it burned a little hotter to burn off nay crud buildup
i would get your O2s and cat fixed because that will also fail emissions too

 

The front O2 sensors help the air/fuel mixture, with them bad your gonna run rich. Replace them and you should be good.

 

^^

turned my novel into a sentence

 

Haha sorry man.

 

tis all right.

yours is much easier on the readers eyes lol

 

Yeah but someone will wanna know more details about the sensors, so your good.