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

Lean fuel, huge consumption, I'm still leaning towards rotten fuel lines

Does it have a return line from the pump to the tank?

 

Its a truck, I rebuilt the carb and it got 16 mpg for a year and a half then I noticed I could watch my gas gauge drop while I was driving. I havent changed a thing with it other than the gas cap. I canged it cause when I would take off fuel would come out the filler neck. Dosent leak with the new gas cap but for some reason the tank builds vaccume pressure.

 

No return line

 

If the extra gas is going to the motor, your tail pipe should look like a oil well.

Where is the gas tank located. Could it be leaking when you are in travel mode?

 

You need a vented cap. Go get one. with the tank building pressure theres a good chance its still leaking from the filler neck, but lower down closer to the tank so you cant see it,

 

I bet you get worse mileage on a warmer day

 

The tank is located behind the rear axle and the filler neck in the stepside fender. After driving ive looked and felt everywere and cant find a leak. Im thinkin its leaking some were and evaportating quickly

 

I didnt mean anything shitty, I just didnt want to suggest a bunch of things you have already tried or considered.
Its got me stumped too. But we will figure it out and get you back on the road.

Have you checked by all connections in the fuel lines? Is it possible gas is forcing itself out while pressurized?

 

That makes sense, thanks ill try that

 

I have checked all connections and nothin. Could be cause of the pressure

 

I doubt it's leaking,,you'd sure as heck know it if you were losing a substantial amount of fuel,,even small leaks are easily noticed due to the rich odor gas leaves behind. Look forward to seeing what solves your problem..

 

OK, you have a posi trac rear end, but only getting power to one wheel? Check your brakes. Are they fully releasing?

 

My rear axle is a 9" ford and I can jack up the rear end and the right axle turns freely. Im sure something broke in there but I have no clunking

 

Good idea.
Check parking brake too.

 

Good thinkin', Randy. OP...Lift the car, and see if all the tires turn easily. Even if they turn easily by hand, if the brakes are loose, they could be binding after braking, and not releasing correctly. Is the car pulling to one side? Heavy tire wear? Or is something slipping? Torque converter? Engine seem to be running at higher rpms than normal?

BTW...this isn't really like a guessing game. More like a mystery or a treasure hunt. Or a game of badmitten...wait...that's not right.

 

I dont have a parking brake and the brakes would start smoking if they were hanging up

 

Ill hook a tach up to the motor and see whats happening there

 

Does the transmission feel sluggish? there are some things that can go wrong with the torque converter, for example, that really hurt efficiency.

Do you park the truck inside or outside?

 

how about a gas leak, only when running, that drips on the exhaust system...thus, vaporizing almost instantly and not leaving evidence of wetness.

just playing the guessing game

 

The truck is real sluggish. I dont know much about auto transmissions

 

I HOPE NOT!!! Hate to see my POS ford burn to the ground

 

I had a van with a 300 and the thing was a pig, although a 1 ton still should have done better. Found out the 3 big screws were loose and the top was loose on the throttle base, leaked bad. But the holes must have been worn, would not stay tight, I could make it better but have to take it off and keep retightening, new carb was the real answer.

 

[QUOTE="T'RANTULA";7421862]The truck is real sluggish. I dont know much about auto transmissions[/QUOTE]


ok we might be hitting on something..sorry was gone for a while target practicing with my daughter

can you push the truck in nutral?
does it feel like it takes off from a full stop with out too much throttle?

the trans might be binding , or like squirrel was saying maybe your converter could be messed up and making your engine work harder than normal for the speed your traveling at

this might be a trans issue, not a fuel loss issue

when you drive it for a while a good 20 or 30 min at good speed, feel the trans pan right when you get out..does it burn your hand? if you spit on it (the trans) does it sizzle?

if you have a heat gun , shoot some temps of the trans case..

I'd find out why your posi aint posi any more

 

Now we're talkin'.

 

The truck pushes like a rock in neutral and it dont like to take off from a dead stop, and the trans pan does get pretty warm but not burning hot. Ive noticed when I stop at intersections theirs a weird smell. Ive smelled burning clutches in a manual trans but that smell dont really compare to this.

 

I don't know which suggestion I like better, this one or "get a vacuum gauge on it".

If the sprag in the torque converter is slipping, it'll drive like a pig till you get it up to speed. From a dead stop it'll barely pull the hat off your head!

Does the trans fluid smell like burnt toast?

 

[QUOTE="T'RANTULA";7421928]The truck pushes like a rock in neutral and it dont like to take off from a dead stop, and the trans pan does get pretty warm but not burning hot. Ive noticed when I stop at intersections theirs a weird smell. Ive smelled burning clutches in a manual trans but that smell dont really compare to this.[/QUOTE]


I think you have your answer boss..

I'd check that rear end..

than move on to the trans if after fixing your rear end dont cure the problem completely,, as said above check the trans fluid smell and color

something went south when you lost your posi..thats why shes hard to push in neutral..

that smell might be your rear end dope over heated and the stench coming out of the vent

make a run and drive it hard, than feel the pig on that rear end

I had an olds 88 that lost its rear end like this ..It was my only ride for a while andd I pushed it hard until she locked up..than it would not move an inch...she got horrible gas mileage until it wouldnt move anylonger

I wouldnt completely dismiss the trans, but with you telling us your posi aint posi any more I'd start there

 

Smells kinda like burning paint and rubber, but the trans fluid smells like normal ATF.

 

The rear end dont get hot, I was gonna pull the right axle but im afraid I wont like what i see

 

Definitely keep focusing on the tranny and cross that off your list, if that isn't it. the rearend issue does worry me. I don't know a whole lot about posies, but aren't there cluch packs in there that can be slipping too...