crappy gas milage: help me figure why

[Anonymous]

I have a
1) 6 month old carb rebuild
2) Redone engine
3) older brake job

and crappy milage

what are the common causes that I can look for?

 

[pedal2themetal45]

HI YA
One of the major causes of bad gas millage is footstomping-pedalsmashing-pistontickling syndorm Brought on by the need for speed... We all get it.. I would check your rt. foot into a rehab facility right away.
Now on the better side
Check power valve size, Timming, Idle speed, (running to fast of an Idle will cause bad mixture setting and bad milage). I don't remember the formula for checking Power valve size. Oh and gas leak..
hope this helps..
Tim

 

[CobraSix]

just found my mileage sink...

TIRES!!!

My tires are max PSi at 44, all 4 of them had crept below 25 psi. Problem with modern tires, is they hold their shape really well at low PSIs, but will still kill mileage. I'm back up to getting around 25 MPG vice my 16 MPG. I filled the tires up this morning to 42 psi cold.

Slade

 

[Anonymous]

isnt 42 really high?

mine were 32 last check

that is a good tought...I never checked them

I DO have foot stopming syndrome...but I think it might be something else..I am going to look for a fuel leak


QUESTION... would changing form my stock gears help? I THINK I am running the 3.03..
that still confused me...gears and all..

 

[x21]

HI YA
One of the major causes of bad gas millage is footstomping-pedalsmashing-pistontickling syndorm Brought on by the need for speed... We all get it.. I would check your rt. foot into a rehab facility right away.

Yep, thats exactly what killed any hopes of fuel economy for my 200. :roll:

 

[CobraSix]

look on your tires. Most tires are rated to run at 44-50 psi max. That's where you are going to get the best economy, and be able to load your car the most. Most common mistake is people think 30-32 is the normal, just because jiffy lube fills it to that level just to be safe (not implying you are like that, but that has become the basic idea).

 

[Anonymous]

yeah, maybe I am remembering my low profiles on my shelby charger

I dont htink I ever read the ones on the stang..brb

 

[pedal2themetal45]

HHHMMMMM
44LBS I always set my at 32 or so just because thats what I was used to when I started working in service stations in 66 thats what was on the tires then. Never look much sence. Just went out and look at some of the cars in the parking lot.. HHMMM some did said 44lbs Max cold. (13" R"s). The old Bias plys on my truck 715 X 15 says 35 lbs max cold. Guess it pays to look..
Tim

 

[Anonymous]

I think my tires say 35 max psi.

 

[Anonymous]

i just checked...low and behold 44psi

gues where I am stopping on the way home...

 

[Anonymous]

you can get better mileage with a bigger dia tire. i changed from 195/70x14 to 225/75x14. this effectively gives a taller gear ratio.
it is more sluggish off the line but the six has enough low end torque
to handle it. these wont fit on the front. so you have to run big-n-little.
no tire rotation here. since i drive mostly long distance 50 miles ata whack at 70-75 this tire size definitely helped mileage. i plan to change to a higher voltage ignition in the next couple weeks and try the larger plug gap setup i have read about on this forum. hoping to hget from 22 up to 25 mpg.

 

[Anonymous]

still, I must be doing something worng...I have 205/70/15's I beleive

and I already have the pertronix and wider gaps...and all that

still...13mph

I am questioning a loose rear end...play in the differential I noticed before....I changed the ujoint and was told play in diff...

I should check for a dragging brake too

 

[CobraSix]

yeah, the old tires use to fill up at 30-35 psi. All of my current tires, low profile (have some 255/45s ZR-17s) or not, are between 40-50 psi cold max. I routinely run max psi, best mileage, though sacrifice some ride comfort...wait, I drive a 65 mustang, what ride comfort? Tires have come a long way since these cars came out.

Slade

 

[Anonymous]

I missed that memo...

d'oh

I will let you guys know if that helps...I hope it helps like 8-9mpg

 

[CobraSix]

over the 80 miles I drove today, it improved the mileage about 4-5 MPG, and that was with a 20 MPH head wind this afternoon for 40 miles.

Slade

 

[Anonymous]

slade...where you driving...the frozen tundra?

 

[CobraSix]

feels like it sometimes...

Slade

 

[XFlow_Fairlane]

whoo don't be overinflating like that....

tires shoudl be filled for max contact patch n teh road. overinflate and the patch will shrink and you will get real bad center wear on the tread. I work in a tire shop and see this all the time.....people coem in wiht the centers cupped on the tires from being overinflated. 35 should be the max you run. going up will just give wear problems not to mention the saftey issue of a tire that is in poor contact with the road for braking

Nick

 

[Anonymous]

nick..I am all about gas milage right now

I checked...FR was 24psi, others were between 30-34ish

now all 42...lets see with one tank where this goes

 

[CobraSix]

running at max PSI is not overinflating. That is max pressure where you still have proper contact patch. If I want max contact patch, I lower to 20 psi.

Our family business vehicles(which averages about 500k miles a year on 5 vehicles) have always run 10% below max psi. We run fully loaded vehicles on the highway. Never had a problem with cupping, so long as you get quality tires. Get cheap tires, you get problems.

Slade