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Change Driving Behavior The easiest way to improve gas-mileage is to change the driver. Aside from going on a severe diet, drivers can change the way they operate the car. This called 'hypermilling.' Various sources claim a 25-33% improvement in gas mileage. The usual gas saving tips aren't any more helpful than they are obvious. What drivers need are some immediate positive or negative feedback on their actions. There are devices that do this with much more grace than a back seat mother-in-law. These driver feedback devices all plug into the Onboard Diagnostics Port (OBD II port). The OBD II port is always located near the driver's left foot at the base of the dash. All of these devices that utilize the OBD port can also diagnose check engine lights. If the check engine light comes on you can find out exactly what is causing it. That alone will pay for the product after two or three check engine lights. I think it's important to understand that all of these devices here only show calculated fuel consumption. They cannot measure the actual fuel consumption. The calculated fuel consumption is based on a few known parameters such as mass air flow, manifold air pressure, engine rpm, and then assumes are few things such as a constant 14.7 air to fuel ratio, a constant volumetric efficiency, and sometimes a correction factor is thrown in. In other words, these are NOT accurate. But they are precise. It's possible to repeat the conditions and get the same result. And the accuracy is 'good enough' for the average user. Just keep in mind that if you see 99mpg or 300mpg for a moment, it isn't necessarily true.
PLX Kiwi This little device costs about $250 and advertises savings of $500+ after one year. It has a color screen with pretty graphics. It constantly grades the driver on the Kiwi score while monitoring four (up to 26) vehicle parameters. The Drive Green mode shows drivers how to maximize efficiency through lessons. The Kiwi also diagnoses check engine lights. If improving gas mileage through altering your driving habits is the primary goal, this is the tool to get.
DashDAQ The premium option is the DashDAQ. The $700 price tag let's everyone know it (it can be had for about $550 if you shop around). The DashDAQ is a small Linux computer with a bright color touch screen, multiple open source programs for monitoring vehicle behavior, and all the connections necessary to connect to any original or aftermarket engine management systems. What puts the DashDAQ on this list is the Fuel Economy program that functions somewhat like the Kiwi. Other programs include, engine diagnostics, custom gauge display, data logging (from over 2000 parameters), drag strip test, 0-60mph braking test, Dynamometer, a lap timer (with GPS option), and an optional GPS system.
Auterra DashDyno This is a very powerful tool and compares somewhat to the DashDaq. But the interface is a much simpler black and white screen with buttons to the side. What puts this device in this list is the ability to measure a calculated instant and average fuel economy. It also has a dynamometer program, engine diagnostics, data logging, sensor data display, and custom sensor inputs. It also records GPS data from an external GPS system. The Auterra Dashdyno can be purchased for $300 to $400 depending on where you shop.
Scangauge II At $170 this is the least expensive option. It does what the Kiwi does but with a lot less class. Four buttons and a small display just big enough for abbreviated words shows why. Despite its appearance, however, it is a very capable device. It monitors calculated fuel consumption, and can display a variety of live vehicle data. Like the other devices it is also diagnoses check engine lights.
For Cars Built Before to 1996 If your car was made before 1996 and is not OBD II compliant none of these devices will work for you. But don't lose hope just yet. Vacuum Gauge For cars made before 1996 there's another option out there. A simple vacuum gauge. The vacuum gauge monitors air pressure in the manifold. If the engine is moving a lot of air (and fuel) at high rpm, the air pressure in the manifold will be about equal to the atmospheric pressure and the needle would point to maximum (0 inches of mercury). If the engine is cruising down the highway under low stress, then the engine will pull a strong vacuum in the manifold. The needle on the gauge may read below 20 inches of mercury. To conserve fuel, change your driving behavior so that the needle stays low. Accelerometer Devices Accelerometers measure changes in acceleration. There isn't a way for these devices to measure or monitor gas mileage. It is possible to use these for a calculated guess as to how much power the engine is generating. I don't have much faith in the accuracy or repeatability of these. For iPhone users there is iRev and Dynolicious. For $200+ these iPhone apps can be connected to the OBD-II port for more vehicle data. But glory is fleeting. Technologies like the iPhone are superseded in months, and the old software may not work with the new iPhone. This was a problem I had with Injectoclean's diagnostic tool for the Handspring Visor. The original Visor's are now part of our fossil record! Other accelerometer devices include the G-Tech Pro and RaceLogic systems. The G-Tech Pro is an inexpensive consumer-oriented windshield mount device. The RaceLogic system is a professional racetrack telemetry system. These are used by automotive journalism such as Road and Track.
Gas Saving Tips Don't go over the speed limit. Air resistance increases with speed. An increase in fuel consumption will be required to compensate. Accelerate before the hill, and then coast up letting the car naturally decelerate as it reaches the top. This reduces the work an engine has to do to climb a hill. Remove excess weight. Kicking out passengers that won't split the gas bill is a good way to reduce weight. Stay in a higher gear to keep the engine rpm low. This works really well with a few engine modifications like an engine reflash and some bolt-ons to improve low-end torque. Cruise control does help. Cruise control maintains vehicle speed, not low engine speed. In most cases the cruise control will change engine speed less than the human driver that results in a gas mileage benefit. A vehicle moving at a constant speed stores kinetic energy that reduces the work an engine has to do. Keep tires properly inflated. Look on the inside of the driver door (near the latch) for proper tire pressure. If the car is front heavy like most front wheel drive cars, keep the rear tires under less pressure than the front for better rear traction. A difference of more than 10 psi between the front and the rear is excessive. Use careful judgment. If you're not sure, keep the pressure the same on all four tires. Get an alignment. Energy is being wasted if all the wheels aren't pointed in the same direction. Drive relaxed. The Mythbusters TV show had a great episode where they compared the gas mileage between angry and relaxed drivers on a closed course. The relaxed driver used 33% less fuel than the angry driver. Keep the tailgate up on your pickup. This was on Mythbusters too. What NOT To Do Don't shut the motor off during a stoplight. That would be a great way to find out that the battery just died. In fact, you'd let everyone else behind you know that your battery died. And then the police would show up to point out the idiot who turned their car off in traffic. And then you can pay for a tow truck and a new battery. Don't use low rolling resistance tires (LRR). These are dangerous. If the car can't stick to the pavement then your steering a sled. The car needs to adhere to the pavement to brake and turn effectively. Seriously, don't use LRR rated tires. Don't accelerate toward a stoplight. That's what New Yorkers do. Don't accelerate really really slowly. It saves about 1% at best when compared to normal or brisk acceleration. Don't avoid the gas station. Driving on empty won't extend your gas mileage. It may prolong the moment the credit card is swiped at the pump, but it won't change the amount you pay per mile. You'll pay the same amount per mile if you fill up every 1/4 tank or every 3/4 tank. If you run out of gas you better have a close friend with a gas can and time to spare. Or pay $100 for a tow truck.
Step 2: Reprogram the Engine
Step 3: Improved Maintenance
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