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You can't tuna fish... · 2 October 05

Fuel Economy Window Sticker

By now you’ve probably read Consumer Reports article about published vs. real-world fuel efficiencies. Up to 90% of the cars they tested had much worse fuel economy than that shown on the window sticker, some up to 50% less!

What is interesting about the article is that they mention automaker’s have been tuning cars for better performance rather than fuel efficiency, primarily because that’s what they’ve felt the market has wanted over the past few years. Let’s not go into the “what we want” aspect of it, but what about this tuning business?

Used to be two types of tuning you could do on a car: maintenance and peformance. Maintenance consisted of keeping everything within factory specs: changing oil & filters, replacing or adjusting sparks and points, and touching up the lube and air pressure. Performance tuning might mean putting higher performance parts into it: replace or tweak the carburetor, crank up the coil voltage, custom shaft, specialized plugs, maybe even install a turbo.

Nowadays much of the system is electronic and under computer control. No points or timing to speak of. There are sparkplugs but with better ignition control they tend to burn clean and last much longer. With the old cars you’d adjust everything to a baseline and hope the ignition advance mechanism would adjust for times when the engine needed higher performance. Computers now monitor all of the salient points of the engine and modify performance on the fly.

Kind of takes all of the fun out of it.

Cars use fuel injection now, which consists of little micro switches programmed to provide precise squirts of gas to the engine at just the right time, followed by an equally precise electrical jolt to the spark plug. It sounds pretty straightforward, but how and when all of this is done determines how much horsepower the engine has, the type of emissions, and fuel economy.

ECU and Engine flow

Computers aren’t mind readers and obviously we never get to tell our car what kind of performance or efficiency we’d like to have. Someone, or something, has made all of these decisions for us. On-board car computers are pre-programmed at the factory for a certain behavior.

Which brings us to an interesting niche market: performance tuning. There’s a whole industry geared around auto performance. The neighborhood rice-boy with the tricked out lime-green civic, coffee can exhaust, and wobbly wing might also be running a specialized chip to squeak out a little more from the engine. The focus used to be on chip tuning, but nowadays it mostly involves messing with the ECU (Engine Control Unit)


From a search of the net it appears most of the after-market chipsets or computers are targeted at the performance market. Companies like Hypertech, EuroChips, Powerchip, Superchips, Jetchip, and Bully Dog to name a few. Most of them offer products tuned to a specific vehicle to increase performance (HP) with a mention that it “might” improve fuel efficiency as well.

No idea how much, or even if, any of these work but I’m kind of surprised that none of these guys are offering programming to optimize fuel efficiency. Better yet, wouldn’t it be cool to get an offer from the automaker to alter your car’s programming for better fuel economy? That would be an excellent good-will gesture to engender customer loyalty. A lot easier and cheaper than coming out with a line of hybrids.

Here’s a few related articles for your Sunday reading pleasure: Eye on Electronics, Hot Chips, and a whole pile-o-technical articles.

Comments 2
  1. — Kendall    Oct 04, 2005 02:05 AM    #
    The cynic in me says that it’s a big conspiracy between the auto makers and the oil companies. :)

    Auto makers won’t admit that they didn’t tune the car to get the best mileage. At best, they’ll tune their cars to better meet the EPA listings.
  2. — Alex    Oct 04, 2005 15:17 PM    #
    Talked to an engineer friend of mine about this. I believe that the tuned ships basically just put the car into “performance mode” all the time rather than the usual JDA mode that is used for emissions testing.

    In any event, driving style, roof rack, how clean (exterior), tire pressure, driving style, and driving style probably have waaaay more influence on your milage than the chip.