EFI Tuning Fundamentals: Reflashing a Factory ECU
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Reflashing a Factory ECU
04.35
| 00:00 | - While the majority of aftermarket ECUs function in a relatively similar way, the way a factory ECU's tables look and function is often a bit different. |
| 00:09 | In this module, we'll gain some insight into how a factory ECU's fuel and ignition maps are laid out, and how they differ from a standalone ECU. |
| 00:17 | In the standalone ECU world, the speed density principle is the most common approach to calculating airflow into the engine. |
| 00:24 | While speed density systems are still used in some OE ECUs, by far the most common technique is to directly measure the mass airflow by means of a mass airflow sensor. |
| 00:35 | Since the ECU knows from the mass airflow sensor what mass of air is entering the engine as well as the amount of fuel the injectors can provide from separate tables, it becomes relatively straightforward for the ECU to decide what injector pulse width to supply to achieve a target air/fuel ratio. |
| 00:52 | For this reason, when it comes to the fuel delivery, the majority of OE ECUs will include a table that simply defines the target air/fuel ratio that the engineers want the engine to run. |
| 01:03 | There's no need for the tuner to directly, or indirectly, tell the ECU what injector pulse width to provide like we would in a standalone ECU. |
| 01:12 | We simply request a specific air/fuel ratio and the ECU does the hard work for us. |
| 01:17 | The load axis in an OE ECU also looks a little different to what we might expect to see in a standalone ECU. |
| 01:24 | Since the load input is the mass airflow sensor, it's typical for an OE ECU to derive the load axis from the mass airflow as well. |
| 01:33 | This may be defined in a variety of units, including pounds per minute, grams per second, grams per cylinder, or grams per revolution. |
| 01:41 | Another common technique is to use the MAF sensor as well as other inputs on the ECU to calculate a load value that's expressed as a percentage. |
| 01:50 | Since OE ECUs spend much of their time operating in closed loop mode at cruise and idle, where they using the oxygen sensors in the exhaust to target a stoichiometric air/fuel ratio, in some cases, a complete 3D fuel target map isn't even necessary. |
| 02:06 | Particularly in a naturally aspirated engine where the load is relatively consistent at wide-open throttle, the ECU may not include a fuel table or air/fuel ratio target table at all. |
| 02:17 | This technique is used in some GM ECUs that include a power enrichment table. |
| 02:22 | This is a 2D table that defines the target air/fuel ratio versus RPM that the ECU should use when the engine is operating in open loop mode. |
| 02:32 | Another table in the ECU will define the throttle position when the ECU should transition from closed loop, where it targets 14.7:1 to the open loop, power enrichment air/fuel ratio targets. |
| 02:45 | This actually makes tuning the fuel delivery incredibly simple for the tuner. |
| 02:49 | However, the accuracy of control in any ECU that relies on a mass airflow sensor is dependent on the accuracy of the MAF sensor calibration. |
| 02:57 | While we can expect it to be accurate on a stock, factory car, any modifications to the intake can potentially affect the MAF calibration and hence the accuracy of the ECU's load calculation. |
| 03:10 | The ignition control in an OE ECU will look relatively similar to what we may be used to seeing in a standalone ECU, except again, the OE ECU will normally be using mass airflow as the load input. |
| 03:24 | The units here mirror what we discussed for the fuel table. |
| 03:27 | One last point I want to mention when it comes to the fuel and ignition tables in an OE ECU, is that often there will be a high octane and low octane table for each. |
| 03:38 | These tables are linked to the knock detection system in the ECU, and are designed to protect the engine from damage from knock, if the engine happens to end up operating on low octane fuel. |
| 03:48 | In this case, generally the low octane ignition table will have less advance than the high octane table, and the low octane fuel table may also target a richer air/fuel ratio. |
| 03:59 | What's important to take away from this module is that while reflashing a factory ECU often works differently manufacturer to manufacturer, let alone when compared to an aftermarket standalone unit, they're just different approaches to achieving the same thing and ultimately, the way the engine responds to fuel and ignition timing will always be the same. |
| 04:19 | As tuners, we just need to understand what systems have been employed by the OE manufacturer and from there we can work with the factory tables to make our changes, leaving all of the hard calculation work up to the ECU. |
