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Old 10-07-2012, 04:00 PM   #1
6lug
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Member#: 108817
Join Date: Feb 2006
Default 18.4 psi max reading for AP2.

https://docs.google.com/spreadsheet/...nR3NGhMWklLZFE

^Datalog for 19psi target boost setting

2004 STi
K&N Drop In
Gutted UP
Maddad 3" divorced DP and mid
Prodrive 2.5" axleback
Everything else power-wise is stock.

Started playing with tuning the boost. Did some searching and found some info saying the AP2 only reads up to 18.4 psi. This sucks, but whatever. But I had done the tune and datalog before I knew about this piece of info. Max boost PSI read in that datalog is 18.46, but I consistantly saw my boost gauge at or a little above the 20 psi mark.

1. Since the AP will only read 18.4 psi, will somthing like TD error only read to correspond with that pressure? (As in, it wont tell me Im 1.7 psi low of 19.1 psi target because its only trying to regulate to 18.4 psi?)

It would seem to me that the ECU still wants 19.1 psi (but the AP just can't read that), so it would still show the other parameters accurately. But in the words of some, this could be "flawed logic".

2. If my boost gauge is reading 20 or 21, does that mean I am overboosting? Is my gauge that accurate I guess is what I mean?

I would think that b/c I cant log over 18.4 that the boost gauge needs to be trusted, especially since when running a 17 psi target boost map, the gauge seemed to correlate to the datalogs.

So now that it seems I answered my own question #2, here is how I started the tune for more boost...

Pulled a few degrees of timing advance from engine loads of 2.25 and up. Added a little bit of fuel (nothing crazy that would soak the cylinder walls, just around 10.5 - 11 : 1-ish). I did NOT reduce WGDC in the areas of target boost. I left them where they were for the 17 psi map.

3. Should I lower the WGDC and then bring them back in until I see closer to 19 psi on my boost gauge? Is that the best way to tune for a higher psi since the AP2 wont read that?

4. I just want to make sure I can tune to my boost gauge, and if I can do that, that the AP will still read the other things associated with tuning boost accurately. Or should I just stick with the 18.4 the AP can read and be happy with what I can get out of that?

Sorry for the long drawn out way of questioning this.

Thanks
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Old 10-07-2012, 05:03 PM   #2
Cobb Tuning
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Member#: 4803
Join Date: Mar 2001
Location: Austin, DFW, Portland, SOCAL
Default

Quote:
Originally Posted by 6lug
https://docs.google.com/spreadsheet/...nR3NGhMWklLZFE

^Datalog for 19psi target boost setting

2004 STi
K&N Drop In
Gutted UP
Maddad 3" divorced DP and mid
Prodrive 2.5" axleback
Everything else power-wise is stock.

Started playing with tuning the boost. Did some searching and found some info saying the AP2 only reads up to 18.4 psi. This sucks, but whatever. But I had done the tune and datalog before I knew about this piece of info. Max boost PSI read in that datalog is 18.46, but I consistantly saw my boost gauge at or a little above the 20 psi mark.

1. Since the AP will only read 18.4 psi, will somthing like TD error only read to correspond with that pressure? (As in, it wont tell me Im 1.7 psi low of 19.1 psi target because its only trying to regulate to 18.4 psi?)

It would seem to me that the ECU still wants 19.1 psi (but the AP just can't read that), so it would still show the other parameters accurately. But in the words of some, this could be "flawed logic".

2. If my boost gauge is reading 20 or 21, does that mean I am overboosting? Is my gauge that accurate I guess is what I mean?

I would think that b/c I cant log over 18.4 that the boost gauge needs to be trusted, especially since when running a 17 psi target boost map, the gauge seemed to correlate to the datalogs.

So now that it seems I answered my own question #2, here is how I started the tune for more boost...

Pulled a few degrees of timing advance from engine loads of 2.25 and up. Added a little bit of fuel (nothing crazy that would soak the cylinder walls, just around 10.5 - 11 : 1-ish). I did NOT reduce WGDC in the areas of target boost. I left them where they were for the 17 psi map.

3. Should I lower the WGDC and then bring them back in until I see closer to 19 psi on my boost gauge? Is that the best way to tune for a higher psi since the AP2 wont read that?

4. I just want to make sure I can tune to my boost gauge, and if I can do that, that the AP will still read the other things associated with tuning boost accurately. Or should I just stick with the 18.4 the AP can read and be happy with what I can get out of that?

Sorry for the long drawn out way of questioning this.

Thanks
The AP version 2 and current AccessTUNER software has no limit to reading boost. Really old v2 AccessPORT versions or AccessTUNER software (older than at least a couple of years) could potentially be limited to 18.4 or ~23 psig, but you could simply update your firmware using the AP manager software and update your software by re-requesting it (for Race versions). version 1 AcessPORT (i.e. black brick shaped device) was limited to reading 18.4 psig.

Bill
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Old 10-07-2012, 05:12 PM   #3
6lug
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Join Date: Feb 2006
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Thanks for the quick response. That makes that entire post obsolete huh?

Except now that means my boost gauge isnt accurate past like 18psi....
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Old 10-08-2012, 10:07 AM   #4
Cobb Tuning
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Location: Austin, DFW, Portland, SOCAL
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Originally Posted by 6lug View Post
Thanks for the quick response. That makes that entire post obsolete huh?

Except now that means my boost gauge isnt accurate past like 18psi....
Your boost gauge was reading over 20 psig during this particular run? If so, there is definitely something wrong with the gauge. I would just make sure you are matching the gauge reading with the run. It is certainly possible for you to hit 20 psig, say, in higher gears when you weren't logging.

Bill
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Old 10-08-2012, 02:13 PM   #5
6lug
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Join Date: Feb 2006
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Yes, during all these runs, the boost gauge would read over 19, even though my targets were set at 19.1 and I was logging 18.46 max (see log above). The gauge was accurate at 17 psi targets (standard OTS Stg 2) and during logging. This is the first I noticed the gauge not being accurate. If it was like one psi off, I wouldnt have been too concerned but it looked to be past the 20 psi mark. I only logged WOT in 4th gear, 2500-RL. This is where I noticed the discrepancy. I will confirm this later today after work.

Last edited by 6lug; 10-08-2012 at 02:39 PM.
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Old 10-08-2012, 05:46 PM   #6
6lug
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Join Date: Feb 2006
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https://docs.google.com/spreadsheet/...mU2MGVIYmhJTnc

https://docs.google.com/spreadsheet/...m43MjB0X3RpUXc

Two more logs from today. 19.3 max psi, gauge reads 23. Both runs it peg'd at 23psi. Again, 4th gear pulls. Any thoughts? Like I said, on the OTS stg 2 map, at 17.4 psi or whatever, the gauge matched up. I'm only asking for another 1.5 psi...how could the gauge be so far off?

I read another thread (must have been old bc it referenced the 18.4 max psi for an AP) and they were debating whether the gauge was more accurate than what the ECU saw. Said something about the ECU reads MAF and some other stuff but the gauge reads actual relative pressure so that's actually what your engine is seeing...I can't remember exactly. I'll see if I can find it. Edit: here's the thread... http://forums.nasioc.com/forums/show...gauge+accuracy
Edit again...appears to be bad info. Didn't read far enough...


I just don't want to be blowing up the motor but all my other data looks good...no knock and all that. But 4 psi difference bw the gauge and the AP has me a bit on edge. Would my WGDC have anything to do with this? And bottom line on the gauge vs the Datalog (which being the one to trust with this discrepancy)??

Last edited by 6lug; 10-08-2012 at 07:11 PM.
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Old 10-09-2012, 11:53 AM   #7
Cobb Tuning
NASIOC Vendor
 
Member#: 4803
Join Date: Mar 2001
Location: Austin, DFW, Portland, SOCAL
Default

Quote:
Originally Posted by 6lug View Post
https://docs.google.com/spreadsheet/...mU2MGVIYmhJTnc

https://docs.google.com/spreadsheet/...m43MjB0X3RpUXc

Two more logs from today. 19.3 max psi, gauge reads 23. Both runs it peg'd at 23psi. Again, 4th gear pulls. Any thoughts? Like I said, on the OTS stg 2 map, at 17.4 psi or whatever, the gauge matched up. I'm only asking for another 1.5 psi...how could the gauge be so far off?

I read another thread (must have been old bc it referenced the 18.4 max psi for an AP) and they were debating whether the gauge was more accurate than what the ECU saw. Said something about the ECU reads MAF and some other stuff but the gauge reads actual relative pressure so that's actually what your engine is seeing...I can't remember exactly. I'll see if I can find it. Edit: here's the thread... http://forums.nasioc.com/forums/show...gauge+accuracy
Edit again...appears to be bad info. Didn't read far enough...


I just don't want to be blowing up the motor but all my other data looks good...no knock and all that. But 4 psi difference bw the gauge and the AP has me a bit on edge. Would my WGDC have anything to do with this? And bottom line on the gauge vs the Datalog (which being the one to trust with this discrepancy)??
The boost reading you are logging is based on the manifold absolute pressure (MAP) sensor reading. You would want to trust that over any boost gauge unless you have a valid reason to suspect that there's a problem with that sensor. Boost gauges are much, much more likely to have issues and it doesn't mean their error will be static across different pressures. It could get worse at higher boost levels while be fine (or a less noticeable error) at lower boost levels.

A quick confirmation that your MAP sensor is working properly is to check its reading against baro. pressure with the ignition on and engine OFF. Should be pretty close to one another (won't be exactly the same necessarily). But, factory MAP sensor issues are very rare.

Bill
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