Fuel Economy...7 MPG? WTF?

[85 Cutlass Brougham]

Well, I am stumped. I put 3 gallons of fuel in my tank, drove about 20-25 miles and it's all gone. These miles were in the rain too, so I wasn't pushing it that hard because I am allergic to death. The engine seems to be running right, and it is a very mild 350. I have an overdrive trans, Quadrajet and 3.23 gears too. I tried to find a leak tonight at a gas station (the car's second home...) and found no leaks at all. The thing is, the gauge needle seemed lower when I got in the car than when I shut it off after driving it 2 days ago (the last time I had driven it). I am wondering where it is all going? Could it be the charcoal canister vent line ( I have it open, but have not put the canister back in yet)? Could the heating of the day be causing it to puke a significant enough amount of fuel in a day to be noticed on the gauge without having the car reek of fuel when I walk by it? (The car sits next to my front door, so I would think I would smell it.) The car has not always been this thirsty and it used to get 15 mpg or so in the city. The way it is now, I can't afford to drive it anywhere because it costs me $8 to go 25 miles.

 

[Blake442]

Your car is off the computer, right?

How about the engine temp? A thermostat that is stuck open can lead to a rich running motor that hogs down the fuel.

Choke pulling off completely? Another scenario that creates a rich environment.

Any reason to believe the cat. converter is plugged?

How do the plugs look?

Have you replaced those old plug wires you talked about yet?

Do you use your parking brake? Dragging shoes can kill mileage as well.

 

[1evilregal]

could possibly be the canister line you talked about...battling the same problem with my f1oo, but fount the vent line from tank to filler was leaking and puking fuel after right hand turns....now if I can only find a decent hose, as they have to be made from a certain type of rubber, and is about 3/4"....

funny thing is, I was getting 11 mpg when the thing was running like crap, now it's running better than ever and I lost 2 mpg...contemplating putting the bad wires and on old carb back on it!!

 

[dan2286]

Does the engine actually seem like it's running rich? Something may be messed up in the carb from it sitting.

 

[megaladon6]

first thing first, make sure the engine IS running right. check the plugs for fouling, timing, vacuum etc. also check for fuel leaks with the engine running. it's possible that it's a small leak and the fumes are whipped away in the airstream. regardless, i'd plug the CC line for now, just in case.

 

[DRIVEN]

You didn't mention a locking gas cap in your spec sheet. Someone "borrowing" your gas at night? :?

 

[85 Cutlass Brougham]

Well, the car is no longer operable after the spectacular wheel bearing failure tonight, but I will give an update as to what I did to try and remedy the problem.I determined that I had set the carb too rich when I was trying to compensate for the tank rust, and had not reset it after I cleaned the carb out. So, I reset it as lean as it would go and still run right. I also had noticed a rattling in the exhaust the last few times I ran it. I looked around and found nothing loose, but tapping on the cat revealed the source of the noise. Yeah, I probably ruined the cat with the rich mixture. So, now I need to fix the damage caused by the bearing failure, replace a rusty gas tank, and fix the catalytic converter somehow...

So, so much for testing my theories on why it sucks gas. I may well have fixed it today, but it will be a few months before I will know for sure. What is odd about the whole thing is that it did not have the normal symptoms of wheel bearing failure. No vibration, no drone, etc. It just went. Odd, huh? As for the repairs, I will use this as my excuse to do the tall spindle swap and my bump steer geometry correction theory.

To try and answer the other questions, it rarely runs over 180 degrees, and I have a mechanical gauge that is mounted directly to the water neck. As for theft, I considered it, but it is unlikely they would target this car multiple times due to the rust contamination in the tank. Plus, the car rarely has fuel in it, and the truck is never missing fuel and it is usually kept with fuel in it. I don't have a computer on the thing, and I run a 2 way cat, not a 3 way like GM did. The plug wires are still old, and I still can't afford to replace them yet. As far as the plugs go, I didn't check them yet either. They aren't old, but I do know that they should be read.

 

[megaladon6]

gotta ask, why bother with a cat? you're in Fl, you don't need it.

 

[85 Cutlass Brougham]

gotta ask, why bother with a cat? you're in Fl, you don't need it.

Let's just say that for legal reasons I won't go any further into how I could potentially fix the issue. It may be any one of a number of possible configurations in the end, I just have not decided which it will be just yet...

 

[Phoenyx]

Cut your cat open, gut it out, and weld it back shut.