Need some N75 valve help
06-27-2003, 03:51 AM
#1
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Need some N75 valve help
I am chasing my boost loss issue and thinking about the N75 valve. I know there are 3 lines to it. One is from the compressor housing (I'm assuming in to measure boost), one is to the wastegate (I'm assuming out to control how much the wwastegate is open) and the third one I have no idea. I reused the original lines when I put the stage 3 in, so I'm wondering if one of these being leaky can cause the N75 to request less boost like this.
<img src="http://web.njit.edu/~dxd0835/raykhan/boost.jpg">
I have changed out my BPV already and that doesn't seem to make a difference. I know I need to do some more logs to see what the engine is doing, but I thought I would ask and see what people think about this.
<img src="http://web.njit.edu/~dxd0835/raykhan/boost.jpg">
I have changed out my BPV already and that doesn't seem to make a difference. I know I need to do some more logs to see what the engine is doing, but I thought I would ask and see what people think about this.
06-27-2003, 04:13 AM
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its doesnt get readings from those lines. the line from the compressor is your air pressure supply
which is then distributed to the wastegate and the fuel evap (emission) system. the control is from the electrical lines.
you can check the line to the evap, you will get more psi to open the wastegate if there is a restriction to this line (thats basically the function of the N75).
you can check the line to the evap, you will get more psi to open the wastegate if there is a restriction to this line (thats basically the function of the N75).
06-27-2003, 04:23 AM
#3
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you can log the N75 control values from block 114...
... and see if the ECU is controlling the N75 and that the N75 is working properly. Then see if the actual boost follows the n75 control.
Kirk
Kirk
06-27-2003, 04:28 AM
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I'll check that, but the requested boost looks like the problem
the requested boost is going down. I don't think it's the software, pretty sure I should be getting a constant 1.3 barr. I wonder where else to look.
06-27-2003, 04:30 AM
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isn't that what I have...boost vs requested boost?
I'm trying to figure out why my requested boost is falling off the 1.3 barr that is should be til redline.
06-27-2003, 04:42 AM
#6
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aren't we all...
... trying to keep max boost till redline.
Checking the wastegate duty cycle tells you how much boost the ECU is asking the turbo to make. If your N75 is at 95% and you still have a boost loss then its time to start looking for leaks or checking the MAF.
You can also log your MAF data to see if the air the turbo is sucking in, follows with your actuall boost readings.
Kirk
Kirk
Checking the wastegate duty cycle tells you how much boost the ECU is asking the turbo to make. If your N75 is at 95% and you still have a boost loss then its time to start looking for leaks or checking the MAF.
You can also log your MAF data to see if the air the turbo is sucking in, follows with your actuall boost readings.
Kirk
Kirk
06-27-2003, 05:30 AM
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my MAF readings have always been a tad low
so maybe that is a clue. But I don't want to pny up for MAF just to find out.
What kinds of values am I looking to see with wastegate duty cycle? Thanks, I appreciate the help.
What kinds of values am I looking to see with wastegate duty cycle? Thanks, I appreciate the help.
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06-27-2003, 08:41 AM
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That doesn't look too bad....
The N75 does whatever the ECU tells it do, so the actual boost should follow requested boost, which it does.
The N75 has one inlet (pressure source) and two outlets, one for the wastegate, and the other is a vent (on mine it goes into the turbo inlet)
It's basically a bleed-off valve. It bleeds off pressure going to the wastegate, and depending on how much it bleeds off, it opens or closes the wastegate
That small dip there might be because the ECU was decreasing the boost, realized it dropped too much, but the N75 valve wasn't quick enough to respond to bring it back in-line. Not much you can do about that though.
I think you need to find out why it's decreasing the boost in the mid range. Log timing and O2, and see if they are off for some reason, maybe due to knock, or high intake temps.
The N75 has one inlet (pressure source) and two outlets, one for the wastegate, and the other is a vent (on mine it goes into the turbo inlet)
It's basically a bleed-off valve. It bleeds off pressure going to the wastegate, and depending on how much it bleeds off, it opens or closes the wastegate
That small dip there might be because the ECU was decreasing the boost, realized it dropped too much, but the N75 valve wasn't quick enough to respond to bring it back in-line. Not much you can do about that though.
I think you need to find out why it's decreasing the boost in the mid range. Log timing and O2, and see if they are off for some reason, maybe due to knock, or high intake temps.