06-12-2011, 10:34 AM
Before fiddling with your pump, its a good idea to have a read through my other guide - BOSCH VE GUIDES - Pump setup and fine tuning.
The LDA housing is the top part of the pump with 4 bolts holding down a dome shaped lid with a bolt in the top. The LDAâ??s job is to control and limit the fuelling per the boost pressure. See the below diagram to help understand how the system works:
![[Image: bosch_ve_lda.jpg]](http://i789.photobucket.com/albums/yy175/DanHargrave/bosch_ve_lda.jpg)
When the throttle shaft rotates the governor pushes on the leverset, which pushes a small dowel against the LDA â??pinâ??. The LDA pin is a shaft with an eccentric cone at the lower end. The cone is designed so it is very adjustable by just rotating it to more/less aggressive angle, and it is therefore rotated by the manufacturer to the desired angle to give a set level of fuel per boost pressure.
By rotating the pin to a steeper part of the cone, the dowel that is pushed by the leverset can travel further and will allow more fuel to be injected. As standard the XUDâ??s LDA pin is set on almost the shallowest setting and is also limited at the bottom, by the screw on the top of the LDA housing and at the top end by a small plastic washer.
When setting up your LDA for the best performance the first steps are usually to wind the screw on top out almost all the way OUT (which lets the pin sit higher up, and allows less fuel off boost) and then to remove the plastic washer (which will let the pin go down further under pressure, allowing more fuel on boost). The locknut on the top is a 13mm, which needs to be slackened and then the screw in the middle should have a torx head in it which you then use to wind the bolt out, before tightening the locknut back up. To remove the plastic washer you will have to undo the 4 bolts holding the lid down (Usually either flathead bolts or torx). Once that is removed you will be able to see a rubbery diaphragm with a metal disc in the middle. You need to hold the metal disc and rotate it 360 degrees and then gently pull it up. It should come out fairly easy with a little bit of wiggling, do not use any force or you will damage the dowel that rides on the pin! If it doesnâ??t come out easily try rotating the diaphragm again. Once that is removed you should be able to see a star wheel with a spring sitting on top of it and the small plastic washer inside the spring. Simply pick the washer up to remove it and put it somewhere safe, like in the bin or on the floor.
Once you have done the above you now have 2 choices. You can either rotate the LDA pin to a more aggressive slope or you can grind the pin to create an even more aggressive slope, giving further off/on boost fuel control. By looking at your LDA pin, you should be able to see which side is the more aggressive (Itâ??s the right hand side on the photo belowâ?¦)
![[Image: LDApin.jpg]](http://i789.photobucket.com/albums/yy175/DanHargrave/LDApin.jpg)
Once you know which side of the pin you want to use, replace the pin in the hole with the chosen side facing to the left, the side which dowel comes in from.
If you want to grind the LDA pin you need to remember that the dowel pushed by the leverset can only move inwards about 60% of the thickness of the LDA pin (~6mm) See the below dimensions of a standard LDA pins eccentric cone:
![[Image: LDAconedimensions.jpg]](http://i789.photobucket.com/albums/yy175/DanHargrave/LDAconedimensions.jpg)
When at the stock side of the cone there is a maximum of 2.01mm of â??rangeâ?? between min and max fuelling. When at the aggressive side there is a maximum of 2.25mm of â??rangeâ??, so although by rotating the pin you will get more fuel at full boost, you will also get more fuel off boost, and you will only gain 0.24mm of extra range (the difference between on and off boost fuelling). This is where grinding the pin becomes effective. By grinding in at â??aâ?? in the above photo, we can grind up to a maximum depth of 5.8mm and therefore end up with a range of 5.4mm!
Please note though, grinding the max end of the cone any further than 5.8mm will potentially cause problems with the seal inside the pump around the dowel. To grind the cone any further it is necessary to make â??otherâ?? modifications to the pump internally, which would allow the dowel to travel further and give more on/off boost range.
Also, when you have ground your pins slope to the desired angle, make sure the new surface is very smooth. If its rough it will wear down the end of the dowel and if it is uneven it would make on boost fuelling/power very stuttery and un-smooth.
Here is a photo of a ground LDA pin as an example of what to aim for:
![[Image: GreatYarmouth-20111109-00952.jpg]](http://i789.photobucket.com/albums/yy175/DanHargrave/GreatYarmouth-20111109-00952.jpg)
The last thing you can do to modify your LDA at this point is adjust the pre-load. If you remove the large spring, which sits under the diaphragm you will be able to get to the star wheel, which it seats on. If you look you will be able to see the star wheel is on a threaded section, meaning it can be adjusted to sit higher or lower and therefore make the spring higher/lower and apply more pressure to the underside of the diaphragm. This means that the diaphragm can be made easier or harder to push down with more/less boost. If you have hard fingers you may be able to turn the star wheel with your fingers and thumb, if not you may need to use a flat head screwdriver to rotate it. Adjusting this involves a large amount of trial an error, but what you are essentially trying to do is make the LDA pin harder to push down, so that extra fuel is not injected until full boost is achieved. If this spring is too soft the LDA pin will be pushed all the way down (and therefore full fuel injected) at far to lower boost pressure.
Generally you donâ??t want the LDA pin to be fully down until you are at ¾â??s of your full boost, but it is hard to work something like that out mathematically (I have triedâ?¦) so the best rule is to just wind the spring up a turn or so for every 5 psi over stock. Also note, if you wind the star wheel up to high the spring may become coil bound, meaning the LDA pin will not be able to travel all the way down.
Thanks, Dan.
The LDA housing is the top part of the pump with 4 bolts holding down a dome shaped lid with a bolt in the top. The LDAâ??s job is to control and limit the fuelling per the boost pressure. See the below diagram to help understand how the system works:
When the throttle shaft rotates the governor pushes on the leverset, which pushes a small dowel against the LDA â??pinâ??. The LDA pin is a shaft with an eccentric cone at the lower end. The cone is designed so it is very adjustable by just rotating it to more/less aggressive angle, and it is therefore rotated by the manufacturer to the desired angle to give a set level of fuel per boost pressure.
By rotating the pin to a steeper part of the cone, the dowel that is pushed by the leverset can travel further and will allow more fuel to be injected. As standard the XUDâ??s LDA pin is set on almost the shallowest setting and is also limited at the bottom, by the screw on the top of the LDA housing and at the top end by a small plastic washer.
When setting up your LDA for the best performance the first steps are usually to wind the screw on top out almost all the way OUT (which lets the pin sit higher up, and allows less fuel off boost) and then to remove the plastic washer (which will let the pin go down further under pressure, allowing more fuel on boost). The locknut on the top is a 13mm, which needs to be slackened and then the screw in the middle should have a torx head in it which you then use to wind the bolt out, before tightening the locknut back up. To remove the plastic washer you will have to undo the 4 bolts holding the lid down (Usually either flathead bolts or torx). Once that is removed you will be able to see a rubbery diaphragm with a metal disc in the middle. You need to hold the metal disc and rotate it 360 degrees and then gently pull it up. It should come out fairly easy with a little bit of wiggling, do not use any force or you will damage the dowel that rides on the pin! If it doesnâ??t come out easily try rotating the diaphragm again. Once that is removed you should be able to see a star wheel with a spring sitting on top of it and the small plastic washer inside the spring. Simply pick the washer up to remove it and put it somewhere safe, like in the bin or on the floor.
Once you have done the above you now have 2 choices. You can either rotate the LDA pin to a more aggressive slope or you can grind the pin to create an even more aggressive slope, giving further off/on boost fuel control. By looking at your LDA pin, you should be able to see which side is the more aggressive (Itâ??s the right hand side on the photo belowâ?¦)
Once you know which side of the pin you want to use, replace the pin in the hole with the chosen side facing to the left, the side which dowel comes in from.
If you want to grind the LDA pin you need to remember that the dowel pushed by the leverset can only move inwards about 60% of the thickness of the LDA pin (~6mm) See the below dimensions of a standard LDA pins eccentric cone:
When at the stock side of the cone there is a maximum of 2.01mm of â??rangeâ?? between min and max fuelling. When at the aggressive side there is a maximum of 2.25mm of â??rangeâ??, so although by rotating the pin you will get more fuel at full boost, you will also get more fuel off boost, and you will only gain 0.24mm of extra range (the difference between on and off boost fuelling). This is where grinding the pin becomes effective. By grinding in at â??aâ?? in the above photo, we can grind up to a maximum depth of 5.8mm and therefore end up with a range of 5.4mm!
Please note though, grinding the max end of the cone any further than 5.8mm will potentially cause problems with the seal inside the pump around the dowel. To grind the cone any further it is necessary to make â??otherâ?? modifications to the pump internally, which would allow the dowel to travel further and give more on/off boost range.
Also, when you have ground your pins slope to the desired angle, make sure the new surface is very smooth. If its rough it will wear down the end of the dowel and if it is uneven it would make on boost fuelling/power very stuttery and un-smooth.
Here is a photo of a ground LDA pin as an example of what to aim for:
The last thing you can do to modify your LDA at this point is adjust the pre-load. If you remove the large spring, which sits under the diaphragm you will be able to get to the star wheel, which it seats on. If you look you will be able to see the star wheel is on a threaded section, meaning it can be adjusted to sit higher or lower and therefore make the spring higher/lower and apply more pressure to the underside of the diaphragm. This means that the diaphragm can be made easier or harder to push down with more/less boost. If you have hard fingers you may be able to turn the star wheel with your fingers and thumb, if not you may need to use a flat head screwdriver to rotate it. Adjusting this involves a large amount of trial an error, but what you are essentially trying to do is make the LDA pin harder to push down, so that extra fuel is not injected until full boost is achieved. If this spring is too soft the LDA pin will be pushed all the way down (and therefore full fuel injected) at far to lower boost pressure.
Generally you donâ??t want the LDA pin to be fully down until you are at ¾â??s of your full boost, but it is hard to work something like that out mathematically (I have triedâ?¦) so the best rule is to just wind the spring up a turn or so for every 5 psi over stock. Also note, if you wind the star wheel up to high the spring may become coil bound, meaning the LDA pin will not be able to travel all the way down.
Thanks, Dan.