NEED HELP!! My 300 gets 3mpg!!!

On a limited slip I beleive. When I jack the rearend up put the trans in neutral and when I turn the left wheel the drive shaft turns but when I turn the right wheel nothin

 

you know you have a problem with the rear end...I'd start there, and be ready to spend some money making it right..if your ATF isnt dark and stinky..i doubt your trans is the issue, but would make it my second prioraty

how many miles have you put on it like this?

 

put a new fuel pump on it sounds like its pumping the gas out the weep hole to me

 

has engine timing been checked may have fiber gear worn out on cam.

 

That I aint sure about, the rear end was long broke before I started havin the milage problem

 

Let us know what you find..
gotta get back to shootin'

 

It has a gear drive, and I checked that when I dropped the oil pan a while back. I aint sure what timing a 300 sould be at so I put it 9 degrees advanced cause it ran best there.

 

von rigg you are the first high post person that has good to say.

 

[QUOTE="T'RANTULA";7421984]That I aint sure about, the rear end was long broke before I started havin the milage problem[/QUOTE]


a posi that aint a posi...is a problem.. and your fuel consumption issue could have come on slowly due to the problem in the rear getting worse from not addressing it

dont be afraid to start there...if you cant push that truck in neutral and dont think thats a problem..umm dont know what to tell ya than

 

Disconnect the drive shaft with it on Stands and see how the engine "feels" without the rear end and drive shaft connected. Everything I've read so far indicates the rear end is toast.

Yeah,... could be something Trans Related as well, but I'd go to the rear end first since it doesn't act like it's supposed to already. Then work my way forward. Trans rear bearings and such can do some really odd stuff as well, but I'm betting that something gets worse in the rear end as you move....

 

I know its a problem, Ive never taken a 9" ford rearend apart before. Im thinkin I broke an axle. Broke axles in chevys and the axle comes out, but on fords from what I under stand the axle bearing holds the axle in

 

[QUOTE="T'RANTULA";7421535]It has a 1bbl carb and it sprays a mist of fuel when idling. as far as i can tell it runs how its sopposed to.[/QUOTE]I have a 72 f100 with a 300 inch 6 in it as well. You should not be getting a fuel mist at idle. Since it did this after a rebuild of the carb, either the float sunk, or it is not set properly. The other possibility is the needle and seat are hung up in the open position. Your idle fuel inlet is BELOW the throttle plate. So you should NOT be seeing any fuel spray/mist while idleing. I think your fuel pump is okay. I think your float is sticking open and over filling the the float bowl.

 

like you said in a Couple of Post's ago you had this
problem when You Changed the Gas Cap
I think you Put the wrong Cap on

you Need a Vented Cap

I had a 300/c6 Van that got 16 mpg
all day long

just my 3.5 cents

 

That dont look too bad

 

[QUOTE="T'RANTULA";7422022]That dont look too bad[/QUOTE]


sorry that wasnt a posi unit..still looking

 

from what i have read so far these would be the steps to take
1. fix the rear end
2. fix the transmission since having to work harder because of the rear end
3. test fuel mileage still only get 3MPG
4. pull engine complete rebuild of all seals and bearings and anything else that is wrong with it.
5. test MPG again still the same
6. put a for sale sign on it saying gets great gas mileage
7. with the money from the sale get new project.

 

You also said you have a couple bad lifters in the engine, or something? wonder if you have a flat cam? Have you run a compression test on the engine?

 

What should the float be set at?

 

not finding a posi 9" exploded view..anyone got one for him?

 

I havent ran a compression test

 

Mabey the tank isn't empting. How much gas are you putting in?

 

As a last result see if your carb is leaking,Pull it off and look in manifold......

 

[QUOTE="T'RANTULA";7422032]What should the float be set at?[/QUOTE] I will check my motors manual and shoot you a p.m.

 

rochesters are 1/4

 

Is somebody driving your car and disconnecting the speedo that you don't know about

 

Years ago my buddy was driving in front of me in his 68 GTO. He thought that owning a GTO meant use alot of gas. He proceeded to make a wide left turn onto a side street and I watched about two gallons pour out from the back of his car. Found his sending unit seal was rotted away and each turn he was sloshing fuel out. By the time he got anywhere the traces of the leak evaporated so he didn't think he had one. You might have a momentarily huge leak somewhere. I wish you luck in finding the problem.

 

I'm just thinking out loud here...

If the carb was rebuilt, the plugs read clean, and the motor runs well, then there's only a couple of things that could cause a full tank to be an empty tank in just 45 miles. Either the 13 gallon tank holds 13 gallons and there's fuel leaking out somewhere, or there's something in the tank that's causing the tank to not hold a complete 13 gallons.

To the OP - I understand that the tank is 13 gallons, but does it actually hold 13 gallons when filled from empty? Is there any rubber fuel line that could be leaking fuel in an inaccessible place somewhere under the vehicle? What kind of delay is there between filling the tank and going for a drive?

To check for a leak, between the tank and carb, how about disconnecting the fuel line at the carb, then plumbing shop air to that line at 2-3 psi. Spray a soapy water solution on the line all the way back to the tank, around the sending unit, filler neck, everything. If no bubbles, then leaks can be ruled out.

To the question about the gas cap - if there's no return line to the tank, then it seems to me that a vented cap would be in order. As the pump pulls the fuel from the tank, there'll be a small vacuum in the tank that a vented cap would allow to equalize. If a sealed cap were used in a non-return application, then the engine would starve for fuel as the vacuum in the tank came to a point where the pump couldn't pull any more fuel. The vented cap should have an integrated check valve to keep fuel from vaporizing when the vehicle is left to sit.

If the old cap is available, I'd think about filling the tank with 13 gallon, then installing the old cap and immediately going for a drive.

 

I got some kinda death wobble comin from the rearend now. Im gettin rid of the truck now so I guess theres no need to ask anymore questions. Thanks everyone who contributed to this insane problem

 

if you have a return line from the pump to the tank make sure its hooked up. I too thought i was getting 3 mpgs. that dumps a shit load of fuel onto the ground while traveling