engineandecu101
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engineandecu101 [2009/02/26 11:56] twdorris |
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| - | ===== Engine operation and ECU tuning concepts ===== | + | ====== Engine operation and ECU tuning concepts ====== |
| It's simply impossible to give a full account of engine operation and ECU tuning concepts in a couple paragraphs. So please don't take the following as a complete summary of everything involved. It's not. This section is simply intended to orient the reader's mindset in the right direction with some high level concepts. | It's simply impossible to give a full account of engine operation and ECU tuning concepts in a couple paragraphs. So please don't take the following as a complete summary of everything involved. It's not. This section is simply intended to orient the reader's mindset in the right direction with some high level concepts. | ||
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| - | ==== Air flow ==== | + | ===== Air flow ===== |
| The amount of air going into an engine is a critical piece of information the ECU needs to know **very** accurately so that it can accurately calculate how much fuel to inject. If the real airflow going into the engine is different from the amount the ECU thinks is going into the engine, the ECU will schedule an inappropriate amount of fuel and the engine's operation will suffer as a result. So accurate airflow metering is really important. | The amount of air going into an engine is a critical piece of information the ECU needs to know **very** accurately so that it can accurately calculate how much fuel to inject. If the real airflow going into the engine is different from the amount the ECU thinks is going into the engine, the ECU will schedule an inappropriate amount of fuel and the engine's operation will suffer as a result. So accurate airflow metering is really important. | ||
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| - | ==== Fuel flow ==== | + | |
| + | ===== Fuel flow ===== | ||
| From the amount of air the ECU is told is going into the engine, the ECU calculates an amount of fuel required to maintain a 14.7:1 A/F ratio using stock injectors at stock fuel pressure. This is where things can get a little tricky to keep straight in your head. The ECU is coded from the factory to account for the configuration the engine came with from the factory. That is, stock injectors and stock fuel pressure. On a stock 2G DSM, that's 450 cc/min injectors at 43.5psi base fuel pressure. On a stock 1G manual DSM, that's 450 cc/min injectors at 37psi. Stock 1G automatics came with 390s at 43.5psi. This determines the flow rate of fuel into the engine. From that flow rate assumption, the ECU can calculate how long to hold the injectors open to get a specific flow rate required for the air it believes is coming into the engine. | From the amount of air the ECU is told is going into the engine, the ECU calculates an amount of fuel required to maintain a 14.7:1 A/F ratio using stock injectors at stock fuel pressure. This is where things can get a little tricky to keep straight in your head. The ECU is coded from the factory to account for the configuration the engine came with from the factory. That is, stock injectors and stock fuel pressure. On a stock 2G DSM, that's 450 cc/min injectors at 43.5psi base fuel pressure. On a stock 1G manual DSM, that's 450 cc/min injectors at 37psi. Stock 1G automatics came with 390s at 43.5psi. This determines the flow rate of fuel into the engine. From that flow rate assumption, the ECU can calculate how long to hold the injectors open to get a specific flow rate required for the air it believes is coming into the engine. | ||
| So, you have two things now that the ECU needs to have accurate information on. First, it needs accurate airflow to calculate fuel flow requirements and second, it needs to know if you've changed anything that affects fuel flow into the engine. If you change base fuel pressure or you swap in different injectors, you have to adjust the ECU's fuel flow calculations to take this into account. | So, you have two things now that the ECU needs to have accurate information on. First, it needs accurate airflow to calculate fuel flow requirements and second, it needs to know if you've changed anything that affects fuel flow into the engine. If you change base fuel pressure or you swap in different injectors, you have to adjust the ECU's fuel flow calculations to take this into account. | ||
| + | There are two "modes" of operation for fuel control. In both cases, the ECU starts out with airflow data from the airflow sensor and calculates a 14.7:1 A/F ratio using its assumption about injector size and fuel pressure. But in "closed loop" mode, it checks to see how far off this estimate was by monitoring feedback from the O2 sensor. Closed loop mode is typically active during idle and cruise conditions. | ||
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| + | In the other mode, "open loop", it does not check these assumptions. It simply calculates fuel flow requirements and injects fuel. This is the mode the ECU operates in at wide open throttle and a few other conditions (early start up for example). | ||
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| + | ==== Closed loop ==== | ||
| + | Closed loop mode is explained in more detail on the [[fueltrimupdatepoints|Fuel Trims]] page. Please read this page and really understand how fuel trims play a role in closed loop mode of operation. They are very important numbers when it comes time to dial in a new set of injectors, for example. | ||
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| + | ==== Open loop ==== | ||
| + | {{ http://www.ecmtuning.com/images/forums/ecmlink101/2gdsmafr3d.gif }} | ||
| - | ==== Timing (ignition advance) ==== | + | ===== Timing (ignition advance) ===== |
| At some point, air and fuel is going into the engine and getting all mixed up and pressurized by the piston going up on the compression stroke. The ECU then schedules the ignition of that mixture. The precise point at which the ignition takes places is very critical. Firing too early (advanced too far) can cause very bad things to happen as cylinder pressures increase dramatically beyond design limitations and stuff starts to break. Firing too late (too retarded) generally just causes poor performance. So the trick is finding the happy middle ground. | At some point, air and fuel is going into the engine and getting all mixed up and pressurized by the piston going up on the compression stroke. The ECU then schedules the ignition of that mixture. The precise point at which the ignition takes places is very critical. Firing too early (advanced too far) can cause very bad things to happen as cylinder pressures increase dramatically beyond design limitations and stuff starts to break. Firing too late (too retarded) generally just causes poor performance. So the trick is finding the happy middle ground. | ||
engineandecu101.txt · Last modified: 2024/03/15 11:16 (external edit)
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