i just finished putting in a new waterpump in my car, and i noticed i was almost empty on the gas gauge. this would make my mileage on this tank of gas about 200 miles. now, im no rocket science but, that doesnt sound very good. its a stock 305tpi, minor port work done to the plenum, new cap and rotor, new ignition coil, new wires, edelbrock headers, Y pipe, high flow cat, 3inch exhaust to hooker muffler, newly rebuilt 700r4,new oxygen sensor, new battery, alternator, radiator, radiator hoses, IACV, and fuel filter. i did drive the last tank of gas with a bad waterpump(it had bad bearings and was making tons of noise) but whats our tank of gas hold? 15 to 17 gallons? and at 200 miles that makes my MPG if we have 15 gallon tanks around 13MPG and even worse if we have a 17 gallon tank about 12MPG. dont get me wrong my car runs good, has alittle bit of a high idle, but runs good, pulls hard, my sparkplugs are alittle old, and im due for changing them but i also dont have any trouble codes. is 12 MPG pretty much what i should expect? keep in mind this was mostly short trips

My average in-town mpg, on a 170,000 mile stock 350, short of the hi-flow cat & cat back (both Magnaflow), was 15/16.

On the highway, I get 20/21. In town, I was always pushing to hit the 200 mile mark per tank.

Honestly? Thats only like 2mpg lower that the ratings when it was brand new.

But yeah....Your 305 should be getting 18 in town, 23 highwa, IIRC the correct #s.

yeah 18 would be awesome, not to mention i have a new EGR and air temp sensor. but what else could it be? the car feels like its running awesome

A rich running car feels good, the extra power comes from burning more fuel and air, so MPG will be down.

If you get a good tune on the car, you can have both. I get 16-18 town and 22 road with a 383, you are losing some MPG out the tail pipe.

could the hit in MPG be attributed to some sensors out of calibration? because i know that my TPS might be off, and my idle is off aswell

When you pull the plugs look at them and see if it looks to be rich.

Have you done a data log yet or used a scanner?

This type of information would be a big help.

no i havent done a data log or used a scanner, i have a scanner at my school, but im not familiar with using it, does it have to be a special scanner? and it just plugs into the diagnostic port correct?

The scanner will be your friend. Work with your teacher or a buddy, someone will know what to do.

Hard to calculate city mileage. Need to get out on the highway for a long time to get the true mpg. Simply calculating how many miles the car uses to a tank doesn't say much. That will change depending on how empty the tank is and how much gas you put in. Also depends on tank size.

There is a debate about the fuel tank size in our cars. Officially it's 15.5 gallons. But there are a number of us (myself included) who seem to have 12 gallon tanks. Made driving across the country a bit of an annoyance (11 tanks of gas in 2.5 days). There have been TGO members who have run out of gas and only been able to put in 13 gallons. Others have driven up to the gas station and put in over 16 gallons of gas in. Others routinely put 14 gallons in every time.

My car with the fuel pump humming and the car darn near stalling and hiccuping from lack of fuel will be able to get about 12 to 12.2 gallons in there. I'm not talking about high speed cornering. I'm referring to low speed in a mall parking lot.

So fill'er up and get out on the highway. Measure how many miles and how many gallons it takes.

yeah i would say mine is a 13 gallon tank. im pretty sure thats how much i put in last time i ran out of gas.