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Electronic Engine Management Pt.3: Chip Re-Writing – by Julian Edgar One of the best ways of modifying an electronic engine management system is to change the software. If different fuel and ignition maps are programmed into the main memory chip, then different output data will be selected by the ECM in response to the various sensor inputs. The beauty of modifying the ECM in this manner is that there are no physical changes made to the system. The original wiring harness, input sensors, injectors, ignition system and so on can be left unchanged. Also, the outputs from the ECM not directly related to engine performance – like transmission, air-conditioning and cooling fan control – can be left untouched. One of the difficulties in chip rewriting is that the knowledge required to get into the software and make any changes is held by a select few. Secondly, major engine modifications may Intended for a BMW, this Bosch Motronic electronic control module (ECM) features a reprogrammed main memory chip from Fueltronics. 8  Silicon Chip not be easily met by software changes alone. Changing the chip Chip rewriting is currently big business, with basically two different approaches being taken. The first approach is to sell chips on the basis that a change of chip alone will yield useful performance gains. This implies that the original program was not fully optimised in the first place, otherwise how could useful gains be made in a chip produced in the aftermarket scene? In naturally aspirated (non-turbo) cars, a chip-change alone will yield only a marginal power improvement – in the region of 5-10%. As a guide, a performance increase on the road from a chip-change might knock 0.2 seconds from a 0-100km/h time, dropping this time from perhaps 9.8 to 9.6 seconds. This perfor­mance gain generally comes from running a more aggressive (ad­ vanced) timing map, with steeper ramp angles. Extra fuel is injected to match the new timing (a factor that could lead to an increase in fuel consumption). In turbocharged cars, the situation is a little different. With many cars running ECM-controlled turbo boost pressures, the chip-change might also include a lift in boost pressure. The greater gas flows which result from this will give a more sub­stantial power gain – often as much as 20% in round figures. The ignition and fuel maps are also changed to give the correct ignition timing and fuel mixtures to go with the increase in boost pressure. In both naturally inducted and turbo cars, a lift in the rev limiter can also be included in the new software. The rev limiter built into the engine management systems of cars is designed to prevent over-revving, which is potentially very damag­ing to the engine. With the pistons having to be accelerated to full speed, stopped, and then accelerated again in the opposite direction every time the crankshaft turns, the strain on engine parts such as the con-rods is very great. Increasing the engine revs dramatically increases the loads placed on engine components, bringing them closer to the point of failure. Too high an RPM will cause breakage, with perhaps the piston exiting the side of the block or trying to come through the head! However, an engine which is still developing usable torque high in the rev range will yield more power if the engine can rev higher. This is because of the equation: Power (kW) = Torque (Nm) x RPM/9550. In some engines, the manufacturer has been conservative in the rev limit imposed, mostly to improve engine longevity. If a potentially shorter working life is tolerable, then the rev limit can be raised with a power improve- When mechanical limitations, such as fuel injector size, prevent effective software changes, higher capacity components need to be fitted to the engine. The results can be worthwhile, as illustrated in Fig.3. ment. Increasing the rev limit is an engine-to-engine proposition, though. Other engine modifications Much greater power (and potentially economy) gains can be gained if major engine modifications are performed and the ECM software then changed to suit. In other words – as has always been the case – airflow into and out of the engine can be im­­­­­-proved, thus giving potentially more power when mixed with the appropriate amounts of fuel. All of the traditional “hotting-up” methods can be used: free-flow exhausts and mufflers, better air filters, bigger valves, porting the head, different camshafts and so on. Once these mechanical changes have been made, the car can then be “driven” on a chassis dynamometer, with exhaust gas analysis being used to constantly monitor the mixture under different loads. The areas then requiring modification can be ascertained and the ECM software appropriately rewritten. The Power at wheels (kW) SUZUKI SWIFT GTi 1300 RPM Fig.1: this chassis dynamometer graph shows the effect of replacing the ECM chip in a Suzuki Swift GTi 1300 fitted with a DOHC 16-valve engine. No other engine modifications were made. December 1993  9 Power at wheels (kW) NISSAN PULSAR GTI RPM Fig.2: the effect of chip replacement in a Nissan Pulsar GTi 1800 (DOHC 16-valve engine), fitted with a free-flow exhaust system. Power at wheels (bhp) DAIHATSU CHARADE 1.3CRi Road Speed (mph) Fig.3: the effect of chip replacement in a 1992 Daihatsu Charade CRi 1300, fitted with larger fuel injectors. car should then be rechecked in its final form. If done with appropriate expertise, the car should also remain quite legal in terms of its emissions. Sometimes, however, a hardware change will be needed in addition to the software modifications. This could come about, for example, when the engine power has been greatly increased. The original fuel injectors may simply not be able to pass enough fuel, even if held open for long duty cycles. In this case, the original injectors 10  Silicon Chip would then be replaced with larger units and the software reprogrammed to provide short­er pulse widths at all but the highest load situations. With an all-out race engine, the standard ECM may not be adequate and would then be replaced with a fully programmable computer. Chip switches Another approach is to use more than one new software pro­ g ram, with the change over between different programs being ef­fected by a dash-mounted switch. For example, in a turbocharged car, one switch position could give a high boost and rich top-end mixture for maximum power, while another switch position could be for the standard software program. Yet another position could be for lowboost, lean-mixture economy running, while the final switch position could have a blank program. The blank program would be in place as a security measure, to make it more diffi­cult to steal the car! Other alternative switch position Power & torque outputs should be measured on a chassis dynamometer to assess the results of any software or hardware changes. Changing the ECM chip alone will lead to only a marginal improvement in a naturally aspirated car. programs can include a “valet” (or son and daughter) mode, where the rev limiter is reduced to perhaps 4000RPM. Some manufacturers (notably in the United States) have fitted valet switches as standard to their powerful V8-engined sports cars. Rewriting original-equipment car ECM memory chips requires appropriate computer programming expertise, good mechanical understanding, and access to sophisticated equipment such as exhaust gas analysers and chassis dynamometers. The car manufacturers also make it very difficult to gain entry to their software, with encryp­tion codes and other security measures employed. “Breaking in” can take months. There are a few companies in Australia that are modifying car ECM software for specific applications, and a much greater number selling general “hot-up” chips. Many of these chips origi­nate overseas and are being sold by retail outlets with little understanding as to what has actually been done to the program. Chips that aren’t so hot There have also been some interesting tales circulated of “hot” chips which actually retard timing and fuel compared to the standard chip, until the last few hundred RPM where they revert to the original manufacturer’s specifications. The cars drive poorly until the end of the rev range, at which point they appear to go like hell! If you choose to swap the ECM chip alone, then carry out performance and/or chassis dynamometer tests before and after chip fitment – and try to get a money-back SC guarantee. Acknowledgement: thanks to Fuel­tronics (16 Payne­ ham Rd, Stepney, SA 5069 – phone 08 363 2199) for provid­ing some of the information used in this article. December 1993  11