Basic Fuel Economy Driving Techniques and Instrumentation
There's been a lot of talk about how important instantaneous feedback is in achieving high fuel economy, but what role does it really play and how can it be most effectively used? Hopefully we can get into that a little bit here. Firstly you should not that this article will be focused mainly on using the SuperMID since I don't have and can't use a Scangauge. If your car is 1996+ you can check out there Scangauge at their homepage, www.scangauge.com
. Regardless of the device this article will be written in order to discuss how it is used to help you get better fuel economy.
Take a look at this little diagram that I made of the main screen of my MID:
- This tells you the fuel economy you are getting at the very moment and has little bars that fill up the top-middle such that more bars equal greater fuel use and so on. This is highly variable but you will use this feature when featuring the gas, driving with load, and a whole host of other things that are based mainly around a target fuel economy.
- This gives you the average speed for the trip, pretty straightforward. You'll notice, however, that if you're repeating a specific trip a slower average speed will generally correspond to a higher trip fuel economy.
Injector Pulse Width
- Raw data about how long the injectors are open for. This is a good indication of load in my experience as it takes the speed component out of the FE equation and tells you directly how much gas is going in there.
- Records how far you've traveled since resetting the section you're viewing.
- Records how much fuel you've used since resetting the section you're viewing.
Percent Distance with Engine On
- This is one of the neater features of the MID. Because it was originally designed for use with the Toyota Prius to allow FE readings higher than the stock computer could record it was also programmed with a function that records what percentage of the distance traveled is done so with the engine on. In the case of the Prius this would be a ratio between the combustion engine and electric motor, but for us it is a great measure of the use of engine off coasting and engine braking. It records any amount of distance traveled without the injectors opening as time with the engine off, and is a very helpful tool to compare engine off coasting's effect on fuel economy.
Engine On FE
- This is another Prius feature that is very interesting to compare engine efficiency with efficiency of driving technique. You can see that the engine on fuel economy is lower than the trip fuel economy (the difference translated to about 3 MPG) so that even on this very short trip where I didn't do very much engine off coasting I have reaped the benefits!
- Trip FE is either the most important or second most important function of the superMID. Trip FE will allow you to pick routes to work/school, help you figure out if your driving skills are improving, challenge you to do better on every drive, and let you test modifications you've done to the car. Most of the rest of this article will be based around the use of trip FE.
Last KM FE
- The last KM FE is just that, the FE that you've managed over the last KM of distance. This section evens out some of the spikes of the instantaneous FE and alerts you to the fact that you might be getting bad FE due to a slight grade or unnecessary throttle pressure. It's also rewarding to see it pegged at 99.99 KM/L after a > 1KM engine off coast.
SuperMID Daily Driving Tips&Tricks
1. Begin with the most fuel efficient route
- Why spends weeks fine tuning your trip to work when in the end you could've been getting better mileage on some other route? Before you spend all your time trying to max out a certain route experiment with others to help you find out which one is really best. Don't go be straight trip FE, use the total fuel used section to see where you're actually using the least. Make sure that you give each route a fair shake and try to collect data from days with similar weather patterns. Also, be aware of the hypermiling potential that one route might have over another; if one has a steep hill with a gradual downslope and the other has a gradual hill with a steep downslope you are more likely to succeed with the first option. You will spend less time going up the hill and more time coasting your way down. For more information on route selection check out this article.
2. Set goals
- Before the discussion on actual driving tips, you need to remember to set goals, both for tanks and individual trips. The most important thing about goals is breaking them, because every time you smack through a milestone you will be motivated to set another one and break that one too. Start of realistically though. If you've been getting 35 MPG say you want to hit a 40 MPG tank and 50 MPG segment, not too far out of the realm of possibility but certainly beyond what you've been getting.
Another important method of goal setting is to make each particular milestone in your drive a goal in itself. For example, when I drove to school I would do whatever I could to get to 30 MPG before leaving the developement. This was rather difficult as there were many stops and it needed to be done on a completely cold engine, so the challenge was ever present. However, I knew that if I could accomplish this I was set up for a good day in terms of fuel economy. I would also set goals for FE when entering the highway, leaving, and passing other certain major changes in the trip. In this way I could tell whether or not I was on course for my overall goal and could thusly adjust my driving habits.
3. Feather the gas
- This technique is extremely important if you want to squeeze ever last bit of gas mileage out of your car. Generally when you drive you're giving more throttle than you need to to maintain speed or you're constantly and very slightly accelerating. With the superMID you can vary your throttle pressure until you're at your very lightest point while maintaining speed and you'll actually see the increase in fuel economy. Even with this knowledge now I cannot properly feather without the MID, it's just crucial to be able to see the slight differences in pressure and road grade that you would never notice without instantaneous feedback. The MID challenges you to milk ever last MPG from your drive, even when you're just cruising.
4. Slow down
- Speed kills! Aerodynamic drag increases greatly with speed, not to mention engine RPM and load. If you can manage it go 55 on the highway or avoid the main highway altogether. You'll see a huge savings from 65 to 55 MPH, especially if you have short gearing that leaves you cruising at upwards of 2500 RPM.
5. Engine Off Coast
- Engine off coasting is just what it sounds like. When you come to a stop or a span where you can coast without losing speed you shut the engine down. To do so flip the key to I and allow a few seconds before switching back to II. This will disable power steering (if you have it) and your power brakes will only have enough charge for a few stops. Make sure to practice EOCing in an area where you can safely test you car's reaction to this technique. If you're EOCing to a stop simply stop and when you're ready to go key back on. If the EOCing is part of a coast simply key back on when you're ready to restart or bump start by letting the clutch out while in gear to restart the engine.
6. Pulse and Glide
- Perhaps the most intriguing and beneficial of all the FE driving techniques, P&G involves two basic steps. The first is a moderate throttle pulse to a target speed and the second is an engine off coast back down to the lower target speed. The idea behind this technique is that normal internal combustion engines are inefficient during normal cruising but more efficient at moderate throttle. When that moderate throttle is couple to the infinite FE of EOCing you will end up with a higher average FE than if you simply cruised at a steady pace. This is most easily accomplished at low speeds because there is less aerodynamic drag than would be present at higher speeds. So with a low speed P&G you can really increase the distance of your glide. Of course all the same issues apply with P&G that do with EOC, so practice in a safe area and make sure to measure your non-P&G FE first so that you can compare and refine your technique.
7. Drive with Load
- When DWLing you do your best to maintain fuel economy when encountering hills or small inclines. In normal driving you would attempt to hold 45 MPH by increasing throttle pressure, but when DWLing you pick a target fuel economy level and allow yourself to lose speed while going uphill in order to not lose fuel economy. You may then pick up speed on the downhill where you can speed up quickly and without greatly damaging fuel economy. DWL will greatly aid fuel economy but depending on the speed and size of the hill there is a limit to its benefits. If you're in a trafficless area and willing you can bleed off as much speed as you want, but while in traffic you have to consider potential safety issues during DWL.
8. Parking Tactics
- Always park in the highest spot you can find. If your driveway at home has a slope, use it. Roll out into the road before starting and try to use some of that momentum to begin your drive. In parking lots back it in when you park. Reverse is a killer but using it on a warm engine is better than having to reverse out of a spot on a cold engine. If possible find a gap where you can pull straight through and be facing forward in the space so that you do not need to reverse at all. When entering a parking lot scout it out immediately and try to find a spot in a location that you can coast to without using any extra gas. If you can shut off the engine entering the lot and coast into your space you'll have saved a lot of gas that would normally go to first or second gear navigation.
(or lack thereof) - Using the brakes is an awful waste of momentum, try to avoid it at all costs. Anticipate traffic flow and coast to a stop rather than following traffic and braking with it. If you coast early many times traffic will pick up by the time you reach the clog and you will not need to brake at all. Take curves as quickly as possible while maintaining safety. If possible coast to the turn so that you do not need to brake at all. When approaching lights coast first, engine brake second, and then brake as a last resort. If you time things just right you can make most lights and turns without using the brakes at all.
Well, now that that's over with, I should describe some of the other functions of the superMID. As you may have noticed in my picture there is an "A" by the engine on percentage. This corresponds to a trip stored within the superMID, there is A, B, Start, Tank, and Lap. A and B are just arbitrary storage containers, Start records everything since the beginning of the use of the MID (unless it is reset), and Tank records your statistics for the tank. The Lap function stores 20 different laps and is very helpful for testing as you only need to push one button to switch to a new lap. It also allows you to compare the current lap FE to the last lap without switching menus.
Now that you know the tips, tricks, and function of the superMID, go out and get yourself one! If you're seriously interested contact me and I will put you in touch with Yoshi, the maker.
Contact me with questions or comments!
- Ben aka SVOboy