5 mpg WTF?????
Thread Starter
6th Gear Member
Joined: Dec 2006
Posts: 8,007
From: Citrus County, FL
5 mpg WTF?????
so i filled up my gastank, drove about 30 miles within the course of a couple days and i have used a 1/2 tank of gas. please someone tell me how in the f*ck this is possible? i checked under the car for leaks, its not loading up when i leave it idling and it doesnt smell rich, and the holley 600 still has stock jets. btw i wasnt beating it either, just driving around town.
argh!!!!! i swear it used to get like 10 mpg with the 302 and a holley 600. i really, REALLY dont get it
argh!!!!! i swear it used to get like 10 mpg with the 302 and a holley 600. i really, REALLY dont get it
3rd Gear Member
Joined: Jul 2008
Posts: 958
From: Santa Monica, Calif.
Note to my77:
Please remove snow chains until it actually snows, lol.
Seriously, timing retarded? tire pressure down? Idle too fast? Going uphill a lot lately?
Combo of these?
I suppose you checked the obvious stuff but if it's not that then you're just running rich.
The only other thing it might be is your neighbor who could be siphoning your tank at night.
Good luck.
CP
PS: 10 MPG in a 302 600 4v sounds like you burn rubber or run rich a lot. That's high. Stock gears?
CP
Please remove snow chains until it actually snows, lol.
Seriously, timing retarded? tire pressure down? Idle too fast? Going uphill a lot lately?
Combo of these?
I suppose you checked the obvious stuff but if it's not that then you're just running rich.
The only other thing it might be is your neighbor who could be siphoning your tank at night.
Good luck.
CP
PS: 10 MPG in a 302 600 4v sounds like you burn rubber or run rich a lot. That's high. Stock gears?
CP
Last edited by Carlos Pineiro; Oct 14, 2008 at 05:12 PM.
2nd Gear Member
Joined: Dec 2007
Posts: 300
From: Arizona
Obviously it IS running rich or leaking because 5MPG is way off.
You say it USED to be better? What changed?
Has it been sitting for a long time?
Do you have a vacuum gauge? What is the manifold vacuum at idle?
Do the lifters clack like crazy?
Is the tank original? Examine the whole bottom of the fuel tank. I have had tiny pinholes that never dripped but definatly leaked. The only clue is discoloration around the pinhole.
Check or replace all vacuum hoses.
Tighten the carb base nuts. Tighten hose clamps or replace fuel lines,filter, and clamps.
Set the accelerator pump for minimum squirt.
Check to see if the power valve is leaking.
Put a different spring(black color code) in the secondary vacuum unit.
Do you have points or electronic ignition?
What do the spark plugs look like?
My car got like 9 MPG when I first got it. After a whole series of fixes I get 17 in town rock solid.
One step at a time. You will get it right but it may not be easy..
You say it USED to be better? What changed?
Has it been sitting for a long time?
Do you have a vacuum gauge? What is the manifold vacuum at idle?
Do the lifters clack like crazy?
Is the tank original? Examine the whole bottom of the fuel tank. I have had tiny pinholes that never dripped but definatly leaked. The only clue is discoloration around the pinhole.
Check or replace all vacuum hoses.
Tighten the carb base nuts. Tighten hose clamps or replace fuel lines,filter, and clamps.
Set the accelerator pump for minimum squirt.
Check to see if the power valve is leaking.
Put a different spring(black color code) in the secondary vacuum unit.
Do you have points or electronic ignition?
What do the spark plugs look like?
My car got like 9 MPG when I first got it. After a whole series of fixes I get 17 in town rock solid.
One step at a time. You will get it right but it may not be easy..
Thread Starter
6th Gear Member
Joined: Dec 2006
Posts: 8,007
From: Citrus County, FL
i USED to get about 10 MPG was with my 12:1 302, i now have a 9-9.5:1 289, same ported early 351w heads, same 300/300 .500/.500 flat tappet hyd cam, same ported performer rpm intake, same hedman longtube headers, same accel distributor, same MSD 6AL, same etc. etc. etc.
the 600 thats on there isnt the same 600 i had before, but they are both model 4160 600's with stock jetting. the 289 has like 100 miles on it now, everything is nice and fresh and there are no leaks anywhere i can find. i've looked at the carb while running and the back barrels arent dripping or anything. i even thought maybe the fuel pump had a bad seal and was leaking into the crankcase but the oil level is fine and dipstick doesnt smell like gas.
the gastank has been professionally recoated, no chance for leaks. also, its not like it goes down just sitting - only when im driving. im in FL so there are no hills, and the rearend has the same (stock) 3.40 gears it had in it before.
*maybe* retarded timing could have something to do with it, im pretty sure i went back to the stock stiffer springs in my advance when i put this together just to get an accurate base timing (lighter springs seemed to open early and mess up the baseline timing numbers when using the timing light) - but i cant see timing causing a 5mpg drop.
it doesnt smell rich, an it doesnt load up with fuel when idling in gear at red lights or in drive-thru's.
i really am baffled
the 600 thats on there isnt the same 600 i had before, but they are both model 4160 600's with stock jetting. the 289 has like 100 miles on it now, everything is nice and fresh and there are no leaks anywhere i can find. i've looked at the carb while running and the back barrels arent dripping or anything. i even thought maybe the fuel pump had a bad seal and was leaking into the crankcase but the oil level is fine and dipstick doesnt smell like gas.
the gastank has been professionally recoated, no chance for leaks. also, its not like it goes down just sitting - only when im driving. im in FL so there are no hills, and the rearend has the same (stock) 3.40 gears it had in it before.
*maybe* retarded timing could have something to do with it, im pretty sure i went back to the stock stiffer springs in my advance when i put this together just to get an accurate base timing (lighter springs seemed to open early and mess up the baseline timing numbers when using the timing light) - but i cant see timing causing a 5mpg drop.
it doesnt smell rich, an it doesnt load up with fuel when idling in gear at red lights or in drive-thru's.
i really am baffled
6th Gear Member
Joined: Oct 2006
Posts: 6,417
From: Cork, Ireland
i still think there was someone with a hose at your tank. I once had the same issue with heating oil at the house. i mean 5mpg is something like a litre to the mile .. that is crazy. You need a big hole in your gastank to get to that rating while cruising.
The only thing that will help to isolate this is to fill her up. Drive 50 miles (kinda normal) and fill up again to same level. See how thirsty she really is
Kalli
The only thing that will help to isolate this is to fill her up. Drive 50 miles (kinda normal) and fill up again to same level. See how thirsty she really is
Kalli
