Gas Mileage

I have a 97 GMC Jimmy 4X4, 4.3ltr engine. I know in older cars with carberators that you can rebuild them and install smaller jets to increase the gas mileage. They can only be reduced in a small incrument but I have done this before on carberators and got better gas mileage. With the Jimmy, it has Throttle Body intake. Is there a way of decreasing the amount of fuel going through the throttle body or is this all controlled by the computer? Could one of the new Super boxes be used on this vehicle and reprogram the computer for better gas mileage? Any suggestions on increasing the gas mileage?

A Throttle Body controls the amount of air (only) going into the engine. There are one, or two, fuel injectors which spray the fuel into the intaken air. The amount of fuel is controlled by the engine computer. Performance computers are programmed to flow MORE fuel.
Keeping the engine in peak tune, and the use of a LIGHT foot, will bring the best mpg.

There isn’t any way to get better gas mileage. You can fill the tires to 35 PSI and maybe get a feeling that you are trying. You can save gasoline by car pooling and combining all your trips for shopping and by eliminating some trips altogether. If I could get on a bus, I would take one. I used to like that. Mom and Dad asked me how I got home from the airport when I came for a visit. I took a bus 25 miles and carried my duffel bag the last half mile. It takes an effort but it can be done. Good exercise too.

Other than switching to a vehicle that gets better gas mileage, the best thing you can do is drive like grandma. Easy on the throttle, no high speeds, anticipate lights etc. Next make sure everything is in good shape, plugs wires, air and fuel filters etc. Reduce un-needed weight and make sure the tyres are at the specified pressure or maybe a couple PSI over, but NEVER over the MAX pressure listed in the side of the tyre.

Modern fuel systems do far better than you could do with playing with carb jets and you don’t loose any power in the process.

I agree with the others. Keeping the vehicle well maintained and driving like an elderly person are the best ways to improve mileage. Or trading that GMC 4x4 with the 4.3 litre engine for something more efficient…

Reducing fuel flow only increases gas mileage if your fuel mixture was too rich to begin with. An overly lean mixture will also reduce your fuel economy. A lot of older cars were jetted a little on the rich side.

Gas mileage increasing tips. No useless acceleration. Accelerating towards a red light is useless acceleration. Avoid high peak speeds, air resistance quadruples with a doubling of speed and the power needed to overcome it increases by a factor of eight with a doubling of speed. Never ever use engine braking to slow down your vehicle. Brakes throw kinetic energy away, engine braking also throws kinetic energy away and increases fuel consumption too. Look way ahead as you drive, are the cars a half mile ahead all putting on their brake lights? That’s a hint that you may be heading towards a red light that’s not in your view yet. Time to coast. Switch your engine off if you are in a slow drive thru lane or waiting for a train to go by. No, it doesn’t take more fuel to restart your engine than it takes to let it idle. You aren’t doing a cold start after the engine sat for a minute or two, it’s a hot restart and the engine just takes over where it left off when you switched it off.
All the TV reporters say you should avoid jackrabbit starts but I disagree. A car that’s going 60 mph has the same kinetic energy whether it was accelerated like a overloaded 18 wheeler or you accelerated to 60 just short of burning rubber. If you have to accelerate to that speed, you might as well get it over with at your engines most efficient load point which is usually about 60-75 % of wide open throttle. In fact, a lot of gas mileage records were set by using a “pulse and glide” driving technique. The engine is either WOT of switched off. The vehicle is accelerated when the engine is on and coasts for a long way when the engine is off. By doing a jackrabbit start, you can travel the same moving average with a lower cruising speed and the lower cruising speed more than offsets the fuel you used to accelerate to that speed.
Never drive with the engine revving in a low gear. If your in a line of cars that’s heading to a intersection at 10 mph, use second gear or pulse and glide. Don’t rev the engine in first gear to go that speed. If traffic limits your ability to accelerate, shift as early as you can without lugging the engine.

My best so far with a 2008 Toyota Yaris stick shift, EPA rated at 29/36 is 43.29 mpg in mixed town/freeway driving.

I don’t think that selling it will save you money, though it will save on gas money if you get a more fuel efficient car. But you have to buy the new car, and that is undoubtedly more costly than using the excellent fuel saving tips offered by the rest of the gang. You can read more about it at,

With computer controlled injection, its all programed in and based on what the sensors are telling the computer. The computer then determines how long the injectors are open (called pulse width) to spray fuel. So boils down to the basics-good plugs, filters, tire pressure and good maintenance, AND keeping a light pressure on the gas with easy starts and easy stops.