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engineandecu101 [2010/02/26 13:12]
twdorris
engineandecu101 [2014/11/14 08:13] (current)
twdorris [Fuel flow]
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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 42.6psi base fuel pressure. ​ On a stock 1G manual DSM, that's 450 cc/min injectors at 37psi. ​ Stock 1G automatics came with 390s at 42.6psi. ​ 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. 
  
-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.+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 factoryThat is, stock injectors ​and stock fuel pressure. On a stock 2G DSM, that's 450 cc/min injectors at 42.6psi base fuel pressure. On a stock 1G manual DSM, that's 450 cc/min injectors at 37psi. Stock 1G automatics came with 390s at 42.6psi. 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 mass of fuel required for the mass of air it believes is coming into the engine.
  
-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). 
  
 +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.
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 +
 +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).
  
 ==== Closed loop ==== ==== Closed loop ====
engineandecu101.txt ยท Last modified: 2014/11/14 08:13 by twdorris