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Old 02-28-2013, 02:01 PM   #1
Vrooom_Psh
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Default Accessport vs Gauge

Hey thanks for looking. Not sure if this is a real issue or not but here goes..

At idle, my mechanical boost gauge reads ~ 20" of vacuum.

My accessport reads no more than 11".

Is the accessport just not as accurate for reading this kind of thing? Or is my gauge not reading right?

For what it's worth, the gauge is a defi d-gauge.
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Old 02-28-2013, 02:07 PM   #2
mert34
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Access port does not read vacuum in the same units as your defi.
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Old 02-28-2013, 03:29 PM   #3
Vrooom_Psh
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What unit does it read in?
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Old 02-28-2013, 03:32 PM   #4
08_sti
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Originally Posted by mert34 View Post
Access port does not read vacuum in the same units as your defi.
^agreed, my ap reads no more than -11 at idle
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Old 02-28-2013, 07:55 PM   #5
kellygnsd
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Originally Posted by Vrooom_Psh View Post
What unit does it read in?
Probably pounds. What units does your acces port display boost?
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Old 02-28-2013, 10:56 PM   #6
stevejones19
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AP is PSI constantly I beleive.

The gauge is probably reading inHG on the vac. side.
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Old 03-01-2013, 08:11 AM   #7
Cobb Tuning
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Quote:
Originally Posted by Vrooom_Psh View Post
Hey thanks for looking. Not sure if this is a real issue or not but here goes..

At idle, my mechanical boost gauge reads ~ 20" of vacuum.

My accessport reads no more than 11".

Is the accessport just not as accurate for reading this kind of thing? Or is my gauge not reading right?

For what it's worth, the gauge is a defi d-gauge.
Hi there. The Accessport units for "Boost" are always psi. Your boost gauge units are apparently in inHg, which is common for the vacuum side of the gauge and different than the psi units used for "Boost" monitor on the Accessport which is why the values are different between the two.

Bill
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Old 03-01-2013, 08:42 AM   #8
danger1138
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So back to the original question, are the readings via the cobb AP accurate? Such as boost, AFR etc.. Over lets say a gauge reading?
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Old 03-01-2013, 09:07 AM   #9
Cobb Tuning
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Originally Posted by danger1138 View Post
So back to the original question, are the readings via the cobb AP accurate? Such as boost, AFR etc.. Over lets say a gauge reading?
The "Boost" reading on the Accessport is very accurate as it is based on the factory manifold absolute pressure (MAP) sensor reading. The only consideration is that the factory MAP sensor is limited to around 23-24 psig max, but the sensor can be replaced with one that reads higher (which would require simple re-calibration via the Accesstuner software for new sensor).

The "A/F Sens 1 Ratio" monitor on the Accessport (what you would use to monitor AFR) is based on the factory front oxygen sensor. Unfortunately, due to the sensor's placement and an internal limit placed on its reading on the rich side, it is only accurate with idle/cruise and lower boost conditions. With heavier throttle/load, the ECU will switch to open loop and ignore the front o2 sensor, so the ECU does not "need" it to be accurate. Although it still has a reading in open loop, it just isn't very accurate there (it will usually show to be pegged at 11:1 AFR at WOT with OTS tunes).

To accurately monitor fueling, you would need an aftermarket wideband sensor placed post-turbo. While certainly this is a good idea, it is not generally needed for mild mods like stage 1 and stage 2. You can generally get a good idea of fueling issue via the A/F Learning 1 A,B,C,D values.

Bill
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Old 03-01-2013, 12:16 PM   #10
danger1138
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I see alot of people posting here in regards to placing the factory o2 in the down pipe. What are your thoughts on this?
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Old 03-01-2013, 12:34 PM   #11
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Originally Posted by danger1138 View Post
I see alot of people posting here in regards to placing the factory o2 in the down pipe. What are your thoughts on this?
Although the factory front o2 for the 2.5L cars is considered a wideband, changing placement of the sensor that much from what the factory ECU control is designed for is likely to cause idle/cruise fueling oscillations or other issues. Maybe it would be theoretically possible with appropriate as yet not completely known calibration or code changes to the ECU, but, in the end, would probably not be worth the time and effort since you can easily just purchase an aftermarket wideband o2 sensor to monitor fueling and put that in the downpipe. Some are compatible with our Accesstuner software so you can log the rest of the ECU parameters along with the wideband input. You can also get one with an in-car gauge for monitoring fueling on a more general basis when you do not have the laptop with you.

Bill
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Old 03-02-2013, 03:32 AM   #12
Vrooom_Psh
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Well that was a bit of a threadjack but my question still got answered. Thanks Bill!
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