Ways to improve Fuel Economy Write-up

[Sentientbydesign]

With gas prices continuing on their upwards trend, we find ourselves looking for ways to increase our vehicle's fuel economy. Here is a list of things you can do to improve your vehicle's fuel consumption. Some will also improve acceleration and overall horsepower.

Many of you may be skeptical about the realistic savings ($) that these changes can make, but consider this: A 5% MPG improvement on a car that averages 20MPG means you just saved enough to buy yourself a Starbucks coffee every tankful. You'll also be doing the environment a favor by reducing pollution and helping to conserve our natural resources.

The list



Check your air filter- Dirty air filters make the engine work harder to pump in air which decreases fuel economy. Check your air filter every time you do an oil change or after driving through very dusty areas (Thanks to rxm6).

Replace your spark plugs- Poor spark due to worn or fouled spark plugs can rob your engine of both power and fuel efficiency. Recently, we changed the plugs in my wife's 2000 Celica GT. Her fuel economy went from 26MPG to 29MPG with noticeable power gains too.



Clean your MAF sensor- When your Mass Air Flow Sensor gets dirty, it can't accurately measure air temperature and density and the ECU may run your engine rich.



Check your vacuum hoses for leaks or obstructions- This is pretty self explanatory. Basically check the hoses for cracks, holes, or interior build up. You may find that once you take one off, it will crack. You can buy replacement heater hose from Autozone for around $1/foot. Just be sure it’s the correct ID (Interior Diameter)

Check your knock sensors- An old malfunctioning knock sensor can send an erroneous signal to the ECU causing it to continuously retard the timing which leads to poor burn.



Get a REAL injector cleaning.--In tank fuel injector cleaners can improve fuel economy, but the general concensus (members and a few mechanics) is that the Injector Cleaning Kits work much better. This feeds the cleaning solution directly into the fuel rail. Check with your local mechanic or invest with a buddy and buy a kit.

Change your fuel filter- This is a common suggestion for those with poor fuel economy. The fuel filter is relatively cheap ~$10. The changing procedure can be found in the FAQ. This made no difference in my fuel economy, but it might help yours.

Clean out the IACV- The Idle Air Contol Valve sits above your throttle body. When I removed mine, a tablespoon or two of black carbon-like pebbles fell out. The cleaning procedure is also in the FAQ.



Clean out the throttle body- Over time, the throttle body gets dirty with a black coating. Improper filter oiling can cause even more build-up to accumulate. Cleaning this will improve air flow and allow the butterfly valve to work properly.

Clean out the intake manifold- Just as the throttle body can get dirty, so can your intake manifold. There are two basic methods of cleaning it. The first and more labor intensive is to remove the manifold and clean it with throttle cleaner and a cloth. The second is to use Seafoam. See the FAQ for information on using Seafoam.

Catalytic Converter- Most newer cars have two catalytic converts. One is for low exhaust temperatures, the second is for normal operating temperature. Over time, these can get clogged. Have your "Cat" inspected. If it's clogged, replacing it has yielded up to a 2 MPG increase.

Tires/Wheels-As much as we all like fat, sticky tires, we also have to contend with the fact that the less tire surface area that contacts the asphalt, the better our fuel economy. The stickiness of the tires also creates some drag, so for the best fuel economy, stick with OEM recommended width an go with a touring tire.

Inflating your tires slightly higher than recommended (but never above the tire's maximum pressure) can yield some fuel economy improvements. The best thing to do is just to keep your tires properly inflated.

Those 20" rims you paid $2000 for might actually be costing you more every time you drive. The larger the rim (diameter) and the heavier the rim, means your engine has to work that much harder to make those wheels move. If you insist on having huge rims, check into lightweight options like forged rims. They'll save you in the long run.

Also, remember to get an alignment. 1 degree of toe means for every 100 miles, you're dragging your tire 1.75 miles SIDEWAYS. Alignment policies usually start at around $130 for 2-3 years. It's well worth the money.

Check your brakes- What did he say? My brakes?...Yeah your brakes. In some instances, your brakes can begin to stick and drag while you're driving. This extra drag increases fuel consumption and obviously prematurely wears your brakes.

Aerodynamics- This subject is far too difficult to go into detail in this article. It would need 1 or 2 of it's own articles. However, I will touch on a few ideas.



Underbody trays- The underside of your car experiences a lot of turbulence at high speeds. Smoothing out the underside of the car can improve drag and lead to better fuel economy. The catch Don't suffocate your engine bay of air flow. Email me for details.

Tire Diffusers- Don't try this at home! The tires on a vehicle can be one of the biggest drag culprits. Diverting air around them can help reduce drag.

Wings and Body Kits- Chances are, that your wing (spoiler) and body kit are doing more damage to your fuel consumption than help. Most spoilers are purely for aesthetics. And those aesthetics come at a price...DRAG. Same thing for those body kits that provide down force. At high speeds, they create drag as then provide down force.

Weight- This is NOT an opportunity to go to the extreme with weight reduction, but weight does significantly affect fuel consumption. One website stated that 100lb reduction can make a 2% MPG difference. So in a vehicle that gets 20MPG, you could get an extra half mile per gallon by putting those golf clubs in the garage.

One thing to consider is that driving style makes the largest impact on fuel economy. If you accelerate to stop lights, frequently peel out, drive in excess of 75mph on the freeway...etc, your fuel economy will more than likely suffer. On your next long trip, try keeping a cushion between you and the car ahead of you. When they brake, let you foot off the accelerator and try to coast down instead of accelerating right up to them and then braking once you're on their bumper. After they start accelerating away, gently accelerate back to a comfortable speed. The goal is to keep your acceleration at 0. Accleration applies to going faster as well as slowing down. If you don't slow down much, then you won't have to expend extra fuel to speed back up. This type of driving yielded me an extra 3-4 mpg on a 150 mile trip.

Modified by Sentientbydesign at 2:30 PM 4/7/2008
Modified by Sentientbydesign at 11:22 AM 5/5/2008

[BOBCAT]

Nice Writeup

[rxm6]

An additional point I'd like to add to this list, if I may, is to check your catalytic converters. The pre-cats on my vehicle were clogged beyond recognition and replacing them yielded a gain of an additional 2 mpg around town.

Furthermore, I'd like to stress the importance of checking the knock sensor on these cars as sentient mentioned. The knock sensors are in such a position that, as cars age, it will begin to pick up all kinds of ambient noise from the engine, even injectors clicking, and retard the engine timing, thinking its a knock. I personally never use anything lower than 91 and so I bypassed mine. Incidentally, I've never had to worry about it again; however, this may not be the correct option for everyone.

I'd also like to add: clean your air filter. A dirty air filter will reduce your gas mileage, maybe not by much, but a clean one helps.

Finally, I'd like to add a little to what Sentient said about driving style. At a distance of 200 feet drafting a semi-truck, you will see about a 35% increase in gas mileage. The issue with this of course is you will probably being driving 55-60 mph on the freeway. If you are not in a hurry to get anywhere, this is a great technique to save gas.

[Sentientbydesign]

Would you mind if I added that to the write up rxm6? I'll quote you if you'd like?

Noah will be putting this in the Tech Articles once he returns.

[nj1sh]

Man this sucks gas is about 4$ a gallon ....... I remember the good ol' days 1$ a gallon. We didn't care about fuel efficiency.

[maxhopper]

Awesome write-up! I've pointed the article guys here.

[Sentientbydesign]

Thanks Scott!

[Darktide]

Fuel Filter - How about if your filter is in the tank... how easy is that job. I normally like doing the filter but I'm quite scared of the messing around the fuel tank.

[rxm6]

Would you mind if I added that to the write up rxm6? I'll quote you if you'd like?

Noah will be putting this in the Tech Articles once he returns.

By all means...go ahead.

[Sentientbydesign]

From my understanding, the in-tank fuel filters are only supposed to be changed WITH the fuel pump. On the 4th gens there is a little fuel filter right at the firewall.