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Old 01-04-2005, 10:42 AM   #1
xcntrk75
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Default OBD-II and Boost readings…

First question:
Is boost-pressure a reading available and supported by the stock WRX ECU via OBD-II scanning, without the need for an additional sensor?

It appears that various ECU monitors (PSI^3, DD, etc.) obtain boost-pressure values directly from the ECU (where supported). Is this data available at the OBD-II port on a WRX?

Second question:
Does various OBD-II scanner software available support reading this boost data? For example, via ODB-II interface hardware (Elmscan, etc.), can boost-pressure be read via any of the following applications: Digimoto, ScanMaster, OBDlogger, wOBD, etc.?

Anybody successfully running a setup in this fashion please respond!

All other comments appreciated…
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Last edited by xcntrk75; 01-04-2005 at 11:09 AM.
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Old 01-04-2005, 03:36 PM   #2
bofh
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Do a search on me and ODB2. It works, but is not ready for prime time. You get manifold pressure. That is boost plus atmosphere... wODB looks good. Palmer Products (I think) has something as well, but the link is at home, and I am at my fathers. Also, go to openecu.org and look at the things going on there. May be plans for something powerful up soon, and a deal on Scanmaster3. However, I have an elmscan, and I will make it work!
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Old 01-04-2005, 06:42 PM   #3
Gethin
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The time delay getting the data from OBDII would make reading boost not much use. The sample rate is too low......IMHO it's not fast enough.
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Old 01-04-2005, 09:16 PM   #4
xcntrk75
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You know what I don’t understand is the fact that sophisticated ECU monitors such as the DeltaDash utilize the same OBD-II information (via different protocol) as regular OBD scanners which are now just as fast, yet the common response to this question is that scanners are too slow.

DeltaDash can perform “up to or exceeding 200ms” data samples.

ELM Version-2 can perform up to 10 samples per second, or 100ms data samples.


Are these not comparable rates? Aside from this point, the other large factor between them is protocol, with DD utilizing the Subaru Select and ELM using ISO standard… Apparently this where the ECU monitors prevail as the ISO standard appears to only reference a refresh rate of up to 3.5 samples per/second.

So who knows

All I can say is that I’ve been checking out the DeltaDash software and am drooling… Whether they can perform similar functions or not, the DD appears far superior…
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Old 01-04-2005, 09:38 PM   #5
bofh
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You are correct. With the right software, on a new Subaru, ODB2 is just as fast. The problem is finding the right software.
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Old 01-04-2005, 10:47 PM   #6
Jon [in CT]
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Quote:
Originally Posted by bofh
You are correct. With the right software, on a new Subaru, ODB2 is just as fast. The problem is finding the right software.
Wrong. The OBD portion of the WRX ECU responds much more slowly (~6Hz) than the portion of the ECU that responds to the Subaru-unique (aka SSM) protocol.

To log boost readings with an OBD-II scanner, you must first record the manifold air pressure (MAP) while the car's not running (key on, engine off). This gives you the MAP sensor's reading for ambient pressure. You then subtract that ambient value from subsequent engine-running samples to obtain boost pressure.
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Old 01-05-2005, 10:04 AM   #7
bofh
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Quote:
Originally Posted by Jon [in CT]
Wrong. The OBD portion of the WRX ECU responds much more slowly (~6Hz) than the portion of the ECU that responds to the Subaru-unique (aka SSM) protocol.

To log boost readings with an OBD-II scanner, you must first record the manifold air pressure (MAP) while the car's not running (key on, engine off). This gives you the MAP sensor's reading for ambient pressure. You then subtract that ambient value from subsequent engine-running samples to obtain boost pressure.
I have not seen a delta dash pull quicker that 100ms. I have not seen them all, however, so I may be wrong.

On my car, I was pulling at 80ms very few errors.

For a large data dump, like flashing the ECU, the Hz makes a difference. For polling, it is latency that makes the difference. Check out the article at http://rescomp.stanford.edu/~cheshir...s/Latency.html for a good example of why this is so.

As to the math for boost, the barometric fluctuations are small enough that you can just code in a constant. You don't think the boost gages recalibrate every time you start your car, do you?
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