First thing you should do is find out what mileage you are actually getting (although the on-board readouts in every car I've had are very accurate). First, find some "measured mile" markings on a nearby highway and verify that your odometer is correct. Next, fill the tank to the brim, drive it normally for at least a hundred miles, fill it to the bring again and divide the actual miles driven by the number of gallons you needed to refill it = accurate mpg to compare with what your onboard readout says.
The car can be tuned well and driven conservatively to maximize fuel economy .
Defective emission control components and worn out parts can have a serious , negative impact on mileage .
You probably added a lot of drag with your spoilers/skirts/etc.
A gentile foot and tune up might help.
My GTP which was driven with a stage on PCM, cat back exhaust, and 3.0 pulley on the supercharger got 22 mpg. You have the DIC display that shows you the mpg your are averaging. If it's less than the 22 mpg that's about average for the 3.8 liter motor you need to have the engine data read with a Tech II scan tool to make sure the sensors are all working with in spec. Something as simple as the ECT sensor reading wrong will cause excessive gas consumption.The 3.8 also has issues with the lower intake manifold leaking and the fuel pressure regulator leaking into the vacuum hose. If you think the gas mileage is way off have it diagnosed by a mechanic that knows what they are doing. DIYers never have a chance because they don't have the tools or know how.
Patrick, car brand and model names are proper names. These must be capitalized. 1998 Pontia Grand Prix GT is correct. Please edit and correct this problem. MPG. Miles per gallon. Please capitalize this acronym as all acronyms must be. You are asking about the mechanical condition of this car and how you drive it and where this car is driven. the 17/27 MPG was determined under laboratory condition. No wind, no road resistance, no geographical features, no traffic, no weight and no AC running. The concept of these reports is to give the consumer a purchase data point. Most drivers waste over 30% of the fuel they buy. How? Sure. Running the AC when not needed, idling, not keeping the car in top mechanical shape, speeding, carrying weight, etc. But these factors are yours to determine. First of all, forget about these numbers. Totally not realistic. This is a seventeen year old car with close to 200,000 miles by estimates. An worn engine can have 50% of the original horsepower. This ruins its performance. A car not in good mechanic repair as to fuel/air/electrical also uses more fuel. The first step is a mechanic to see what has to be done and what you can afford or is financially wise to spend on this older car. Next step are tires. Tire pressure, alignment, suspension, etc. need to be checked out. What you indicate are serious mechanical issues. That is the first step. Google as to driving knowledge as to MPG. Any speed, no wind, over 55 MPH will cause more fuel to be used due to air resistance. From 55 to 70 MPH wind drag doubles. Once you get these things checked out, determine the MPG the car delivers for your driving conditions. That is reality MPG. Go from there. Good luck.
Other than changing the spark plugs fuel filter and *ignition wires with factory installed AC-Delco parts there is not much else that can be done.
I have a car exactly like yours that gets 32 MPG on the highway in hot weather. The next time you change the motor oil, switch to 5W-30 Mobil1
A larger fuel tank will not affect gas mileage. It will let you go farther between fill-ups, but those fill-ups will take more gas and cost more money.
If anything, a larger tank will HURT your gas mileage because the car will be carrying around more weight in fuel, and weight hurts gas mileage.
Also, it's possible all the body modifications you have done could be having a negative effect on gas mileage. A lot of stuff like that is designed for looks, not aerodynamics, and can actually increase drag.
If you've done the usual stuff like making sure the motor is properly tuned up, tires are inflated, and the front end is aligned, a couple of things you can do are to add lowering springs, and reduce weight.
Getting the car lower to the ground lets less turbulent air under the car, and decreases drag.
Weight requires energy to move, and less weight = less energy needed. You can ditch the spare, rip out the stereo, removed a couple hundred pounds of sound deadening, rip out the air conditioner...how drastic you want to go when it comes to adding lightness is all up to you.
I drive a 1998 Pontiac grand prix gt. I really like my car and want to keep it since I paid a lot for custom exterior parts such as spoiler, bumpers and skirts. But I was wondering if the mpg or fuel economy could be improved. I believe those are the same things but just in case they aren't can you tell me there differences. Could a larger fuel tank be added for will the not be worth it? I believe this car should get about 17 in the city and 27 on the highway. But Im highly positive it doesnt get that, if I drive on 40 mph it burns straight throw my gas. My question is, could that be improved? Or would there be something wrong would my car causing it to burn gas that easily?
