I love my old 1976 Pontiac Grand Prix, so I've kept it for decades. I still want to fix this car up, paint it, and drive it more, but the gas mileage is becoming expensive for my wallet (15 mpg highway - 8 mpg city). Any ideas? This is a 400 cubic inch V8 that will RUN, but I try to feather every move, and still get the horrible 8 mpg in town. The spark plugs are one step hotter than normal, but they are still turn black with carbon. This means running rich, doesn't it? But, how do you fix running rich? cal
2006-12-02 11:43:56 · 10 answers · asked by calumettt 1 in Cars & Transportation ➔ Maintenance & Repairs
disconnect the secondaries in the carb and sit back and calculate how much you are saving on car payments, that should make you feel better :)
2006-12-02 12:00:50 · answer #1 · answered by Anonymous · 0⤊ 1⤋
Pontiacs are my absolute favorite cars. The 400 can be a real world-beater when done properly. If the plugs are black, then its time for a carb rebuild. Does your car have a Rochester Quadrajet? They are absolutely awesome carbs, when built properly. I'm running in the low 12s at 107 MPH with a Q-jet on a 400. I get 8 mpg, but I have 425 horsepower, 3.90 gears in a 3600 lb car.
Pick up Cliff Ruggles "how to build and modify rochester Q-jets". Its the Q-jet bible. Hotter plugs are a bad idea for pontiacs. Use the stock or one heat range colder plugs. Another thing that could be wrong is the distributor curve. Make sure the distributor advance system is working properly. The cat converter can be stopped up too. May need a good dual-exhaust system.
check out www.performanceyears.com
Keep on ponti-yakkin.....
2006-12-02 19:24:28 · answer #2 · answered by electron670 3 · 1⤊ 0⤋
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2016-12-13 18:50:24 · answer #3 · answered by scalf 3 · 0⤊ 0⤋
Everyone else has some good points but you should remember the most obvious one...
A large engine uses more fuel. There is no way around that.
If it has been built to "run", it definitely wasn't built for fuel mileage.
You could always swap out the cam for a smaller one, but you will loose some of your "go".
2006-12-02 13:26:07 · answer #4 · answered by konstipashen 5 · 1⤊ 0⤋
first adjust your carb properly, adjust the idle mixture screws with the pcv out and blocked with a piece of paper
second,make sure your choke is working properly, it should have an electric choke and they will stick
third,adjust your timing advanced more than recommended, it will help with more low end power and better fuel economy
fourth, make sure your spark plug wires are good, your distributor cap and rotor are good and your ignition coil is good, all of these can cause runability problems, also running a better coil and increasing your spark plug gap will help alot
also make sure there are no vacuum leaks, your air filter is mounted properly and clean, your tire pressure is correct and so-on
2006-12-02 12:31:47 · answer #5 · answered by Christian 7 · 1⤊ 0⤋
adjust your carb. give it good tune up. it may be time for a rebuild. i'm guessing that it has a turbo 350 or 400. i would seriously think about getting a gear vendors unit or swapping in a 200-4r cool thing is the 200-4r has the B-O-P bolt pattern. that should help curb your gas guzzling
2006-12-02 12:02:37 · answer #6 · answered by turkey 6 · 1⤊ 0⤋
Big car, Big motor = bad mileage sounds like maybe the carb needs to be adjusted this should be done by someone with experience with carbs.
2006-12-02 11:57:58 · answer #7 · answered by Anonymous · 1⤊ 0⤋
I have a 91' chevy with a 350, and I get 10mpg.
This new gas suckkkks.
2006-12-02 12:00:14 · answer #8 · answered by Mr. KnowItAll 7 · 0⤊ 0⤋
you may want to down jet the carburetor or if it is a 4 barrel you may want to go to a 2
2006-12-02 11:59:22 · answer #9 · answered by daniel h 2 · 1⤊ 0⤋
I would have a good carb mechanic rebuild the carb.
2006-12-02 12:15:41 · answer #10 · answered by Old Guy 4 · 1⤊ 0⤋