Saturday, June 14, 2008
Mini Cooper Electronic Throttles, ECUs, and Fuel
Until very recently, the amount of fuel that went into an IC engine was controlled by a needle valve in a carburetor, which was connected directly to the gas pedal. You pushed the gas pedal down, the needle valve would open, and gasoline would be mixed with the air being sucked into the engine. The further down you pushed the gas pedal, the more gasoline that would go into the engine, and the faster the engine would go.
With the engine speeding up, there was less time for the fuel to explode in the cylinders, so the spark had to occur earlier in the cycle to give the explosion time to really work effectively. This factor is called ignition timing. In most engines, a system of weights and springs inside the distributor would compensate for engine speed, changing the timing of the spark.
The process was all very mechanical. And you were the only brain involved in the system.
Nowadays, it is a wee bit more complicated. First of all, no one uses carburetors any more on street cars. Instead, fuel is added to the air going into the engine with a fuel injection system. A fuel injection system has fewer parts, and therefore is less expensive to make and easier to service, so carburetors have gone the way of crank starters.
A second difference is that, to help meet those increasingly stringent environmental and mileage regulations, engineers have installed a little computer, that ECU we mentioned. The Mini Cooper ECU is connected to your throttle with an electronic connection, so your throttle is more like a big dimmer switch than the lever it used to be. Auto engineers call this a “throttle-by-wire” system.
The ECU tells the Mini Cooper fuel injectors how much gasoline to add to the air flowing into the system and tells the spark plugs when to fire during each engine cycle, changing the amount of gas and spark timing, depending on a variety of factors. This little computer bases its calculations not only on how much you push the throttle pedal, but also on the speed of the engine, the amount of unburnt fuel coming through the Mini Cooper exhaust system and other factors.
Think of it as a little brain that not only breaks your decision—“I want to go faster”—into many smaller decisions about fuel and timing, but also decides sometimes that you really wouldn’t have asked for so much speed so quickly if you knew how much gasoline you were using, and how much exhaust you were pushing into the atmosphere.
In other words, the ECU modifies your decisions in order to help the engine achieve maximum gas mileage and comfortably meet 50-state emission restrictions.
However, within a reasonable range, you would probably want to overrule the computer if you could, or at least modify its decision rules. But for that, you would have to be not only an automotive engineer, but also a computer programmer, wouldn’t you?
Not really. The nice thing is that some good automotive engineers and computer programmers have designed a little computer that you can use to tell your MINI’s ECU to modify some of its decision rules in order to give you better performance. This process is called “remapping” the ECU.
These ECU reprogrammer computers modify the software in your car’s ECU to change the ignition timing and fuel relationships at different engine speeds to improve performance. They also change some other factors, such as rev limits, acceleration enrichment, and fuel mixture so that the engine will be more responsive when you push or release the throttle pedal.
One example of these little gadgets is the “Shark Injector ECU Upgrade” designed and programmed for use on the MINI Cooper S. The Shark Injector is designed to change the program in your car’s ECU to optimize fuel mixture and ignition timing across the entire engine RPM range, but has been programmed to provide a safe margin in order not to risk any damage to your engine.
The Shark Injector is available in two versions, one to upgrade for use of 93 octane gasoline, and one for 91 octane gasoline. The one you use will depend on the quality of gasoline available in your area.
Technically, this is probably the easiest performance upgrade you can make to your MINI. ECU upgrades typically cost around $400. Since you do the change yourself, there isn’t any installation cost.