How Fuel Trim works (how your ECU learns to adapt to your mods)
03-25-2002, 05:15 PM
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How Fuel Trim works (how your ECU learns to adapt to your mods)
Fuel Trim Functionality
Overview
The air/fuel mixture ratio of Hyundai vehicles is controlled by the Engine Control Module (ECM). The ECM controls fuel delivery using two distinct methods depending on engine and driving conditions. The two types of operation are open loop and closed loop. Open loop operation is based on pre-programmed parameters stored within the ECM, which provide standard air/fuel ratios for regular driving conditions. If an oxygen sensor has not yet reached normal operating temperature, the fuel system will function in open loop operation. Closed loop operation is based on feedback from a number of inputs: oxygen sensors, engine coolant temperature, throttle position, engine speed, airflow, and air temperature.
Fuel Trim Control
Fuel injector pulse width is calculated by the ECM during closed loop operation based on engine sensor inputs. The front oxygen sensor indicates to the ECM whether the air/fuel ratio is at the optimum of 14.7:1. If the front oxygen sensor indicates a lean condition, the ECM will compensate by increasing the fuel injector pulse width. If the front oxygen sensor indicates a rich condition the ECM will compensate by decreasing the fuel injector pulse width. On the Scan Tool, fuel trim corrections are shown as a percentage. This percentage refers to a percent change in the overall air/fuel compensation factor. The fuel trim adjustment is ultimately observed as an adjustment to the fuel injector pulse width.
Short Term Fuel Trim
Small adjustments to the fuel trim are constantly made by the ECM. The ECM makes minor fuel trim adjustments so that the air/fuel ratio is close to the optimum air/fuel ratio. These small adjustments are known as the short term fuel trim. On the Scan Tool, the short term fuel trim adjustments are shown as either a positive or negative percentage. No adjustment is represented by zero. A positive number represents an increase in the amount of fuel in the air/fuel mixture (enriches). A negative number represents a decrease in the amount of fuel in the air/fuel mixture (leans). Although the adjustments are usually very small, they can be as large as -25% to +25% or greater. In short, the closer the reading is to zero percent the ECM has to compensate less to keep optimum air/fuel ratio.
Long Term Fuel Trim
Long-term fuel trim makes corrections to the air/fuel mixture based on a series of short-term fuel trim corrections. Similar to the short-term fuel trim values, the long-term fuel trim is shown as a percentage. Adjustments to the long-term fuel trim can be from -25% to +25%. The changes take place over a longer period of time since they are based on the patterns of the short term fuel trim values. The ECM stores these values and "learns" the air/fuel mixture requirements for the particular engine and driving environment. This is also known as "block learning" (see Block Learning section on page 5).
Fuel Trim Monitoring and Diagnostic Trouble Codes
In accordance with OBD-lI requirements, the fuel trim is monitored within operating "cells" or "blocks" stored in the ECM's memory. Each cell represents a specific engine load and RPM range from low engine load and RPM all the way to high load and RPM. Cells 4, 5, and 9 are the primary cells the ECM monitors, because they represent the highest percentage of normal driving conditions for emission purposes. Cell 5 represents an engine load and engine speed characteristic of a normal, sustained driving situation. In other words, the vehicle is being driven at a typical engine speed with a typical engine load for that speed. Therefore, cell 5 is weighted the highest. A fuel trim related DTC can only be set while engine conditions are within one of the weighted cells, 4, 5, or 9. The weight of the cells has been established by OBD-II.
The ECM averages both the long-term and short-term fuel trim values and then compares them to stored failure threshold values. If the failure threshold values for long and short term fuel trim are exceeded for a certain amount of time, a failure is noted by the ECM. If the failure fuel trim occurs within one of the weighted cells, a DTC is triggered and stored in memory along with the fuel trim and other freeze frame data. If the failure fuel trim occurs within a non-weighted cell, no DTC is triggered. Therefore, it is possible for a vehicle to have a fuel trim causing a driveablility condition within certain unweighted cells without triggering a DTC.
Block Learning
The ECM can make small corrections to the air/fuel mixture easily while in closed loop operation. However, in situations where more drastic changes occur, like high altitude operation, the ECM would have to compensate greatly for the lack of oxygen in the air. The response to such an extreme change by the ECM would be slow and performance would be affected. To compensate for such a condition, the ECM uses a method called "block learning". The ECM averages the pattern of fuel trim corrections from each cell or memory block and recalculates the base fuel injector pulse width to accommodate the new driving conditions. As a result, the overall accuracy of the base pulse width is improved. Once the base air/fuel mixture has been recalculated, the ECM only has to make small fuel trim corrections to maintain an optimum air/fuel ratio.
Overview
The air/fuel mixture ratio of Hyundai vehicles is controlled by the Engine Control Module (ECM). The ECM controls fuel delivery using two distinct methods depending on engine and driving conditions. The two types of operation are open loop and closed loop. Open loop operation is based on pre-programmed parameters stored within the ECM, which provide standard air/fuel ratios for regular driving conditions. If an oxygen sensor has not yet reached normal operating temperature, the fuel system will function in open loop operation. Closed loop operation is based on feedback from a number of inputs: oxygen sensors, engine coolant temperature, throttle position, engine speed, airflow, and air temperature.
Fuel Trim Control
Fuel injector pulse width is calculated by the ECM during closed loop operation based on engine sensor inputs. The front oxygen sensor indicates to the ECM whether the air/fuel ratio is at the optimum of 14.7:1. If the front oxygen sensor indicates a lean condition, the ECM will compensate by increasing the fuel injector pulse width. If the front oxygen sensor indicates a rich condition the ECM will compensate by decreasing the fuel injector pulse width. On the Scan Tool, fuel trim corrections are shown as a percentage. This percentage refers to a percent change in the overall air/fuel compensation factor. The fuel trim adjustment is ultimately observed as an adjustment to the fuel injector pulse width.
Short Term Fuel Trim
Small adjustments to the fuel trim are constantly made by the ECM. The ECM makes minor fuel trim adjustments so that the air/fuel ratio is close to the optimum air/fuel ratio. These small adjustments are known as the short term fuel trim. On the Scan Tool, the short term fuel trim adjustments are shown as either a positive or negative percentage. No adjustment is represented by zero. A positive number represents an increase in the amount of fuel in the air/fuel mixture (enriches). A negative number represents a decrease in the amount of fuel in the air/fuel mixture (leans). Although the adjustments are usually very small, they can be as large as -25% to +25% or greater. In short, the closer the reading is to zero percent the ECM has to compensate less to keep optimum air/fuel ratio.
Long Term Fuel Trim
Long-term fuel trim makes corrections to the air/fuel mixture based on a series of short-term fuel trim corrections. Similar to the short-term fuel trim values, the long-term fuel trim is shown as a percentage. Adjustments to the long-term fuel trim can be from -25% to +25%. The changes take place over a longer period of time since they are based on the patterns of the short term fuel trim values. The ECM stores these values and "learns" the air/fuel mixture requirements for the particular engine and driving environment. This is also known as "block learning" (see Block Learning section on page 5).
Fuel Trim Monitoring and Diagnostic Trouble Codes
In accordance with OBD-lI requirements, the fuel trim is monitored within operating "cells" or "blocks" stored in the ECM's memory. Each cell represents a specific engine load and RPM range from low engine load and RPM all the way to high load and RPM. Cells 4, 5, and 9 are the primary cells the ECM monitors, because they represent the highest percentage of normal driving conditions for emission purposes. Cell 5 represents an engine load and engine speed characteristic of a normal, sustained driving situation. In other words, the vehicle is being driven at a typical engine speed with a typical engine load for that speed. Therefore, cell 5 is weighted the highest. A fuel trim related DTC can only be set while engine conditions are within one of the weighted cells, 4, 5, or 9. The weight of the cells has been established by OBD-II.
The ECM averages both the long-term and short-term fuel trim values and then compares them to stored failure threshold values. If the failure threshold values for long and short term fuel trim are exceeded for a certain amount of time, a failure is noted by the ECM. If the failure fuel trim occurs within one of the weighted cells, a DTC is triggered and stored in memory along with the fuel trim and other freeze frame data. If the failure fuel trim occurs within a non-weighted cell, no DTC is triggered. Therefore, it is possible for a vehicle to have a fuel trim causing a driveablility condition within certain unweighted cells without triggering a DTC.
Block Learning
The ECM can make small corrections to the air/fuel mixture easily while in closed loop operation. However, in situations where more drastic changes occur, like high altitude operation, the ECM would have to compensate greatly for the lack of oxygen in the air. The response to such an extreme change by the ECM would be slow and performance would be affected. To compensate for such a condition, the ECM uses a method called "block learning". The ECM averages the pattern of fuel trim corrections from each cell or memory block and recalculates the base fuel injector pulse width to accommodate the new driving conditions. As a result, the overall accuracy of the base pulse width is improved. Once the base air/fuel mixture has been recalculated, the ECM only has to make small fuel trim corrections to maintain an optimum air/fuel ratio.
03-27-2002, 12:43 AM
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so basically when you mod your car your computer will adjust the air fuel mixture to properly compensate for your mods....so is there a need for an engine management system and an increase in fuel pressure?
03-27-2002, 01:04 AM
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The ECU can adjust for mods and add more fuel within the limitations of the stock injectors at stock pressure.
The stock injectors are good for about 200 Crank HP or about 180 to 175 Wheel HP. At that point, you would have increase the fuel pressure or replace the injectors.
There are limits to this system. It reacts fairly slowly. It cannot compensate for Nitrous Oxide useage. Nitrous Oxide adds so much Oxygen to the engine so fast, the motor will blow before the ECU can adjust the fuel trim to compensate. With all N/A Mods, the change in engine efficency is small enough that you do not damage the engine while the ECU is doing it's slow adjust, so no worries there.
To read between the lines in the above article. The Short term fuel trim is being adjusted constantly. When short term fuel trim maxes out for more fuel or less fuel, the ECU switches to the next "richer" or "leaner" fuel map, and short term fuel trim is reset to zero, then starts adjusting again. If Short term Fuel trim maxes out again (either rich or lean) the Long Term fuel trim gets moved to another map (richer or leaner), and short term fuel trim is reset to zero, and starts adjusting again.
For those of you with the OBD-ii cable and software you can monitor the state of your short and long term fuel trim.
The stock injectors are good for about 200 Crank HP or about 180 to 175 Wheel HP. At that point, you would have increase the fuel pressure or replace the injectors.
There are limits to this system. It reacts fairly slowly. It cannot compensate for Nitrous Oxide useage. Nitrous Oxide adds so much Oxygen to the engine so fast, the motor will blow before the ECU can adjust the fuel trim to compensate. With all N/A Mods, the change in engine efficency is small enough that you do not damage the engine while the ECU is doing it's slow adjust, so no worries there.
To read between the lines in the above article. The Short term fuel trim is being adjusted constantly. When short term fuel trim maxes out for more fuel or less fuel, the ECU switches to the next "richer" or "leaner" fuel map, and short term fuel trim is reset to zero, then starts adjusting again. If Short term Fuel trim maxes out again (either rich or lean) the Long Term fuel trim gets moved to another map (richer or leaner), and short term fuel trim is reset to zero, and starts adjusting again.
For those of you with the OBD-ii cable and software you can monitor the state of your short and long term fuel trim.
03-27-2002, 01:06 AM
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QUOTE
Decker:
hehehe, random is there anything you don't know?
wait....what is the average velocity of a coconut laden swallow?
African or European?hehehe, random is there anything you don't know?
wait....what is the average velocity of a coconut laden swallow?
The text comes from www.hmaservice.com I failed to give credit. My apologies there, I did not mean to make it apear that I wrote this article. I simply copied it from HMA.
I put it here so that everyone could know just HOW the ECU adjusts fuel trim and how the ECU adjusts and learns "mods".
