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Low cost OBD-II Display

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Old 07-11-2018, 12:23 PM
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Low cost OBD-II Display

I've got a little time before I can delve into the RX-8 so I'm going to put together a low-cost OBD display to display coolant temp and possibly LT/ST fuel trims.

Anything else that you'd normally grab from OBD-II that you'd like to see? I should be able to decode anything that's a standard OBD message.
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Old 07-11-2018, 12:48 PM
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What platform are you building it around? I've built a digital gauge around an arduino to display signals from the fuel pressure, oil pressure, and oil temp sensors I added but I haven't gotten around to adding a CAN-BUS shield to pull OBD data (or put this data on the CAN-BUS so it can be read via OBD).

I think AFR/Lambda would be good for those running boost. MAF rate is useful for diagnostics but not necessarily needed all the time.
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Old 07-11-2018, 05:56 PM
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I'll probably end up with an arduino and MCP2515 or similar. AFR might be tricky as I assume everyone is using a different controller (the RX-8 has to have narrow band O2 sensors right?).

Rather than building a full logger I thought I'd focus on the info that 80% of the regular owners need. Can always add more later. From what I've read the dash coolant temp gauge is next to useless
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Old 07-12-2018, 06:40 AM
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The RX-8 has a wideband for AFR and a narrowband for cat health.
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Old 07-12-2018, 06:43 AM
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Thatís awesome!
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Old 07-12-2018, 06:46 AM
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Pretty sure the PCM uses the standard SAE PID for it, too.
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Old 07-12-2018, 07:39 AM
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Ok I'll check it out. Thank you
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Old 07-12-2018, 10:24 PM
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I suggest, before you get in too deep, that you look at the Ultra Gauge. The ones I bought were about $60, one for each car. That would be your competition...
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Old 07-13-2018, 12:57 AM
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Everything critical can be read with anything that's capable of reading live data.

So ECT, LTFT, STFT, B1S1 Lambda, B1S2 Voltage, Cat temperature, etc. are all easy to access.

I was looking at a Shinka a while ago for someone else and the owner of that Shinka installed an OBD2 monitor in the dash. It's capable of reading live data and erasing codes(which he needs to do every once in a while since he runs a catless mid-pipe). Not sure about the details on it, though.

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Old 07-17-2018, 12:39 PM
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Interesting. I've got to do a timing belt on my truck this week but I hope to look at this pretty soon.
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Old 07-18-2018, 12:48 PM
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How low cost are you looking for?
Attached is my solution, while not dirt cheap I wouldn't refer to it has expensive either.
Attached Thumbnails Low cost OBD-II Display-2018-05-23-20.48.40.jpg   Low cost OBD-II Display-2018-06-01-18.10.21.jpg  
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Old 07-18-2018, 09:08 PM
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Also while we are on the subject, what are suggested temps to use for warnings for coolant and cat?
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Old 07-18-2018, 10:08 PM
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In my GoodBox I monitor:

- coolant temp and rpm (the 2 things I need to know with precision on the track)
- short term fuel trim and AFR
- intake air temp and something I don't remember

It can only display 2 things at a time, so those are the pairs I've set up. I would love to get cat temp as well, but GoodBox doesn't know about that PID

As for warning thresholds, I start to back off around 220F for coolant temp and I would start to worry about the cat at 1800F+, but the thing with the cat is that it will spike to that on occasion, and backing off often makes it hotter in the short term anyway. So I'm not sure I'd put an alarm on that, more just keep an eye on average temp.
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Old 07-19-2018, 12:45 PM
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Thanks Loki, I added those alarms to Torque this afternoon, I did add one for the cat temp but not as a high priority, I will modify it if I find it coming on too often.
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