Programmable ECUs
A special category of ECUs are those which are programmable. These units do not have a fixed behavior, but can be reprogrammed by the user.
A special category of ECUs are those which are programmable. These units do not have a fixed behavior, but can be reprogrammed by the user.
Programmable ECUs are required where significant aftermarket modifications have been made to a vehicle's engine. Examples include adding or changing of a turbocharger, adding or changing of an intercooler, changing of the exhaust system, and conversion to run on alternative fuel. As a consequence of these changes, the old ECU may not provide appropriate control for the new configuration. In these situations, a programmable ECU can be wired in. These can be programmed/mapped with a laptop connected using a serial or USB cable, while the engine is running.
The programmable ECU may control the amount of fuel to be injected into each cylinder. This varies depending on the engine's RPM and the position of the accelerator pedal (or the manifold air pressure). The engine tuner can adjust this by bringing up a spreadsheet-like page on the laptop where each cell represents an intersection between a specific RPM value and an accelerator pedal position (or the throttle position, as it is called). In this cell a number corresponding to the amount of fuel to be injected is entered. This spreadsheet is often referred to as a fuel table or fuel map.
By modifying these values while monitoring the exhausts using a wide band lambda probe to see if the engine runs rich or lean, the tuner can find the optimal amount of fuel to inject to the engine at every different combination of RPM and throttle position. This process is often carried out at a dynamometer, giving the tuner a controlled environment to work in. An engine dynamometer gives a more precise calibration for racing applications. Tuners often utilize a chassis dynamometer for street and other high performance applications.
Other parameters that are often mappable are:
Ignition: Defines when the spark plug should fire for a cylinder.
· Rev, limit: Defines the maximum RPM that the engine is allowed to reach. After this fuel and/or ignition is cut. Some vehicles have a "soft" cut-off before the "hard" cut-off.
· Water temperature correction: Allows for additional fuel to be added when the engine is cold (choke) or dangerously hot.
· Transient fueling: Tells the ECU to add a specific amount of fuel when throttle is applied. The term is acceleration enrichment
· Low fuel pressure modifier: Tells the ECU to increase the injector fire time to compensate for a loss of fuel pressure.
· Closed loop lambda: Lets the ECU monitor a permanently installed lambda probe and modify the fueling to achieve stoichiometric (ideal) combustion. On traditional petrol powered vehicles this air: fuel ratio is 14.7:1.
Some of the more advanced race ECUs includes functionality such as launch control, limiting the power of the engine in first gear to avoid burnouts. Other examples of advanced functions are:
· Wastegate control: Sets up the behavior of a turbocharger's wastegate, controlling boost.
Banked injection: Sets up the behavior of double injectors per cylinder, used to get a finer fuel injection control and atomization over a wide RPM range.
· Variable Cain timing: Tells the ECU how to control variable intake and exhaust cams.
· Gear control: Tells the ECU to cut ignition during (sequential gearbox) upshifts or blip the throttle during downshifts.
A race ECU is often equipped with a data logger recording all sensors for later analysis using special software in a PC. This can be useful to track down engine stalls, misfires or other undesired behaviors during a race by downloading the log data and looking for anomalies after the event. The data logger usually has a capacity between 0.5 and 16 megabytes.
In order to communicate with the driver, a race ECU can often be connected to a "data stack", which a simple dash board is presenting the driver with the current RPM, speed and other basic engine data. These race stacks, which are almost always digital, talk to the ECU using one of several proprietary protocols running over R5232 or CAN bus, connecting to the DLC connector (Data Link Connector) usually located on the underside of the dash, inline with the steering wheel
ECU flashing
Many recent (around 1996 or newer) cars use OBD-ll ECUs that are sometimes capable of having their programming changed through the OBD port. Automotive enthusiasts with modern cars take advantage of this technology when tuning their engines. Rather than use an entire new engine management system, one can use the appropriate software to adjust the factory equipped computer. By doing so, it is possible to retain all stock functions and wiring while using a custom tuned program. This should not be confused with "chip tuning", where the owner has ECU ROM physically replaced with a different one-no hardware modification is (usually) involved with flashing ECUs, although special equipment is required.
Factory engine management systems often have similar controls as aftermarket units intended for racing, such as 3-dimensional timing and fuel control maps. They generally do not have the ability to control extra auxiliary devices, such as variable valve timing if the factory vehicle was a fixed geometry camshaft or boost control if the factory car was not turbocharged.
Knocking Control:
Knocking controller
Some cylinders of the engine are fitted with analogue knocking sensors which produce 4-20 mA signals proportional to the knocking intensity. These knocking signals are analyzed and a knocking control thus effected.
If the knocking signal exceeds background level, the ignition timing point will be adjusted (delayed) and as a further measure (if applicable) the fuel | air mixture temperature will be reduced and as a last resort, the engine power will be reduced during power mode operation with a specific time constant until the
Knocking signal is once again less than or equal to the background level. Once this is achieved, the engine power is once again raised to the nominal load, but at a higher time constant
Knocking controller & knocking sensors assembly
If, due to knocking, the engine power must be reduced to 50% or less than nominal output, the module will be shut down for reasons of safety.
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