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Who can tell me why my gas mileage sucks????6 MPG

Z

zach78k5

1/2 ton status
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I filled up today and did the math and i got in the neighborhood of 6 mpg on my last tank. I dont drive what i would consider hard.
Here is my setup.
305, 32 in. tires, 3.73 gears, headers, 3 in. single exhast, k&n filter, stock carb, 700R4 tranny. The tranny tends to upshift a little too soon in my opinion and also does not like to downshift when it probably should, without really stomping the pedal. I do a lot of city driving. Could my stock carb be the problem? could the weak 305 be struggling and giving my terrible gas mileage? is the exhaust too big for my engine?
 
Your setup doesn't look like anything that would cause that bad of mileage. I'd run another tank and check it again. Check your timing while you are at it. How does it run?
 
First thing to do is to verify that the odometer is correct. With the taller tires it will show that you've travelled less distance than you really have. So the math makes the MPG look worse than it really is. /forums/images/graemlins/cool.gif
 
Along with tranny or axles, if they have been swapped or rebuilt.

I got 18MPG on the freeway with my 305/700/208/3.08/32" combo, got the same with the 350/465/205/3.42/33" as well. (as a comparison to show that CID and gears aren't all that matter)
 
Size 12 shoe?? /forums/images/graemlins/dunno.gif


/forums/images/graemlins/rotfl.gif /forums/images/graemlins/whistling.gif
 
I'd say your exhaust is too big unless you have a hop-upped 305...hmmm, that sounded wierd using those two words in the same sentence. /forums/images/graemlins/grin.gif
 
Why is a 3" single exhaust too big for a 305?
Seems about right to me. 3" single exhaust definatly wont hurt gas milage.

Maby time for a major tune up or a new/rebuilt carb?
 
When was the last time you did a tune up? Plugs, wires, filter. Check to see if you have any burnt spark plug wires. Yes, I would say the exhaust shouldn't effect it for having single. Dual maybe a differant story. Is your carb leaking or fuel pump? Try starting it up and looking for leaks and spray carb cleaner around carb while runnin and see if the idle changes.
 
I agree , tune it up first, change ALL the filters. Don't forget to replace all the old vacuum hoses. You should be getting great mileage, well great for a 2 ton brick anyway /forums/images/graemlins/k5.gif

I get great mileage with simillar setup , except I have 33's and 3.08's and smaller exhaust , don't even use OD unless I am doing 60-65 on freeway. Usually see highway numbers like Dorian does, and in town I can go 4 or 5 days to and from work ( 45 min drive one way in rush hour ) on a near full tank /forums/images/graemlins/k5.gif
 
With the 3" on a stock motor, he is losing low end power and that's what he needs if he's doing a lot of city driving. Granted going to 2.5 exhaust won't alleviate all the problems but IMO it should be done... /forums/images/graemlins/grin.gif
 
Adjust the TV (kickdown) cable. I did it on mine and it's like a totally different truck. /forums/images/graemlins/cool.gif
 
Yeah , i would definatly adjust that throttle pressure cable. you can damage your trans if it isnt running enough pressure . moving it away from the linkage will give you firmer and later shifts and make the transmission downshift properly for passing gear.but i dont thnk that would effect your gas milage . i think that the speedo / axle ratio / tire size combo is throwing off your #s /forums/images/graemlins/thumb.gif /forums/images/graemlins/usaflag.gif good luck.
 
I just changed plugs, wires, and had the thing tuned up. It actually runs really well. I will check the carb thing. I was reading that a bad fuel pump can actually pump too much fuel and mileage can suffer. Anyone else heard of this?
 
My mileage was really bad when I had a brake caliper hanging up. It wasn't anything I could really feel pulling too bad, just a little, but it was enough to give me horrible mileage.
 
Yeah, i have really horrible fuel mileage as well, trying to push a 3 ton brick down the road and through the wind really sucks the gas down,,,,, /forums/images/graemlins/screwy.gif
 
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