2.0 LSJ Engine: How to tune for return fuel system.
05-13-2008, 08:48 PM
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How to tune for return fuel system.
Okay, now for part 2 of our injector tuning how-to. This one involves tuning for a return style conversion. I am not going to go into detail about the install itself, as that is already covered in other threads. This is strictly meant to address the changes that need to be made to tune for them.
By far, the easiest way to go about this is to first make sure you have good injector tables to start with. It is much easier to make the proper changes to tables that are correct to begin with. If you need help with that part of it, there is a how-to here: How to tune 60lb injectors - 56k = ZZzzzzz... - Cobalt SS Network
So the first step is to decide what you want your base pressure to be. That is the rail pressure with the car running and the vacuum line to the regulator disconnected. By messing with the LSJ injector spreadsheet, I found that my injectors have a static flow of 63.5lbs.hr at a rail pressure of 42psi. I decided to go with that (since that is the highest our ECM supports without using a modifier) and set my regulator at 42psi base pressure. Since I now have a return system with a regulator that references manifold vacuum, the effective pressure will be the same across the board. That means my IFR table will be set at 63.5 across the table like this:
Now set your modifier vs volts to 1 across the board.
Next I need to do some math. My offset table is correct for a fuel pressure of 58psi, with an effective pressure that goes up when the car is in vac and goes down when it is in boost like our cars do stock. Since our cars don’t do that anymore, we need to change this table. Since I set my regulator at 42psi and my offset table is for 58 psi, I subtract and come up with 16. I next go to the converter in HPTuners and convert that to kPa.
So I am running a base pressure that is about 110kPa less than stock. Remember that vacuum raises effective pressure and boost lowers it. I go to my offset vs volts vs vac table. I need to effectively lower my pressure by 110kPa. I choose the -108kPa vac column and I copy
And paste to all of the columns, so that they are the same all the way across.
Keep in mind that I decided to go with a fairly low base pressure, so that I could stay within the limits of my IFR table and to give myself a higher pulsewidth at idle, making it much much easier to tune these things. If you decide to run a higher pressure that puts you above 63.5lbs/hr you will need to use a modifier above "1" to get the correct IFR.
That’s it! Now go tune your MAF and adders…
By far, the easiest way to go about this is to first make sure you have good injector tables to start with. It is much easier to make the proper changes to tables that are correct to begin with. If you need help with that part of it, there is a how-to here: How to tune 60lb injectors - 56k = ZZzzzzz... - Cobalt SS Network
So the first step is to decide what you want your base pressure to be. That is the rail pressure with the car running and the vacuum line to the regulator disconnected. By messing with the LSJ injector spreadsheet, I found that my injectors have a static flow of 63.5lbs.hr at a rail pressure of 42psi. I decided to go with that (since that is the highest our ECM supports without using a modifier) and set my regulator at 42psi base pressure. Since I now have a return system with a regulator that references manifold vacuum, the effective pressure will be the same across the board. That means my IFR table will be set at 63.5 across the table like this:
Now set your modifier vs volts to 1 across the board.
Next I need to do some math. My offset table is correct for a fuel pressure of 58psi, with an effective pressure that goes up when the car is in vac and goes down when it is in boost like our cars do stock. Since our cars don’t do that anymore, we need to change this table. Since I set my regulator at 42psi and my offset table is for 58 psi, I subtract and come up with 16. I next go to the converter in HPTuners and convert that to kPa.
So I am running a base pressure that is about 110kPa less than stock. Remember that vacuum raises effective pressure and boost lowers it. I go to my offset vs volts vs vac table. I need to effectively lower my pressure by 110kPa. I choose the -108kPa vac column and I copy
And paste to all of the columns, so that they are the same all the way across.
Keep in mind that I decided to go with a fairly low base pressure, so that I could stay within the limits of my IFR table and to give myself a higher pulsewidth at idle, making it much much easier to tune these things. If you decide to run a higher pressure that puts you above 63.5lbs/hr you will need to use a modifier above "1" to get the correct IFR.
That’s it! Now go tune your MAF and adders…
Last edited by TommyP; 10-03-2012 at 10:29 AM.
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