Something I mention about fuel pressure control on a common rail.
Many modern engines have digital engine controls that have "closed loop" controls. Rail pressure is closed loop.
What a closed loop control is:
When you have a system like fuel pressure, that is required to change frequently under various conditions, you can do it two ways:
Open Loop: This works by having a look-up table that is already pre-programmed for the expected conditions the engine might forseeably encounter. Our main injection pulse works this way. It sees 3000 rpm, and 100mm of fuel required, then looks up that value in a table and ALWAYS runs that value unless another look up table modifies it, like a water temperature table, or intake air temp table, or altitude table. This only works if you already know every possible value you will ever need. It cannot adjust for wear or unexpected conditions. So it will be wrong occasionally. That's why when you actually calculate the theoritical values that SHOULD be in the main injection table, some don't add up. Our main injection pulse and timing are two examples of this.
Closed Loop: This is a "smart" system. While it does have a lookup table, it's only used for a starting point. It begins using the the value in the table, then looks at what happens by reading sensors. Then it makes an adjustment and looks again. It continuously does this to insure that it is making the system do what is desired. However, if the starting point table is too far off, it will never hit the target values and it usually stops adjusting to a limit value. Our CP3 operation and VNT chargers are this way. When you are seeing wild values on the fuel pressure or boost pressure that aren't the desired values, and nothing is busted, it's because it's original starting wasn't close enough. While I do a simple method that works fine for me (changing the target pressure values), the best way is perhaps adjust the CP3 Current table, so the starting point is closer.
Many modern engines have digital engine controls that have "closed loop" controls. Rail pressure is closed loop.
What a closed loop control is:
When you have a system like fuel pressure, that is required to change frequently under various conditions, you can do it two ways:
Open Loop: This works by having a look-up table that is already pre-programmed for the expected conditions the engine might forseeably encounter. Our main injection pulse works this way. It sees 3000 rpm, and 100mm of fuel required, then looks up that value in a table and ALWAYS runs that value unless another look up table modifies it, like a water temperature table, or intake air temp table, or altitude table. This only works if you already know every possible value you will ever need. It cannot adjust for wear or unexpected conditions. So it will be wrong occasionally. That's why when you actually calculate the theoritical values that SHOULD be in the main injection table, some don't add up. Our main injection pulse and timing are two examples of this.
Closed Loop: This is a "smart" system. While it does have a lookup table, it's only used for a starting point. It begins using the the value in the table, then looks at what happens by reading sensors. Then it makes an adjustment and looks again. It continuously does this to insure that it is making the system do what is desired. However, if the starting point table is too far off, it will never hit the target values and it usually stops adjusting to a limit value. Our CP3 operation and VNT chargers are this way. When you are seeing wild values on the fuel pressure or boost pressure that aren't the desired values, and nothing is busted, it's because it's original starting wasn't close enough. While I do a simple method that works fine for me (changing the target pressure values), the best way is perhaps adjust the CP3 Current table, so the starting point is closer.
Thanks guys for giving him all the help!