Need O2 clamp for EMU
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Newb
Joined: Mar 2006
Posts: 5
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From: Fremont, CA
Need O2 clamp for EMU
Hey folks, I meant to post in this thread: https://www.miataturbo.net/forum/showthread.php?t=13232
... but it seems you've cleaned old threads/posts and my post count has gone to 1, so I can't post in the marketplace area.
I'd like to ask Joe Perez if he can make those or share the documentation so I can make my own.
Thanks!
... but it seems you've cleaned old threads/posts and my post count has gone to 1, so I can't post in the marketplace area.
I'd like to ask Joe Perez if he can make those or share the documentation so I can make my own.
Thanks!
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Joined: Sep 2005
Posts: 34,382
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From: Chicago. (The less-murder part.)
Hey, guys.
I've decided to stop building these, as it's more trouble for me than it's worth. As requested, I'm re-posting the schematic for my EMU-triggered O2 clamp here so that everyone can build their own if they want one. Perhaps some kind mod will sticky this so people can find it more easily in the future.
The resistor values are not absolutely critical. If you have to sub a 4.7k instead of a 4k it's no big deal- it'll just shift the centerpoint on the potentiometer a little. A note about the pot itself, I much prefer to use the more expensive box-shaped 15 or 20 turn units as opposed to the cheap single-turn units. You need a lot of precision when setting this resistor, and a multi-turn makes it a lot easier to set.
The diode across the relay can be damn near anything that isn't a Zener. I've been using 1N4004s simply because I have a pile of them. Use something that has a 1N400x number and you'll be fine.
The regulator probably doesn't need a heat-sink. It's only passing a few ma.
The trigger output of the EMU is 12v. Since I'd been using 5v relays (again, I had a few extras) I had to put a resistor in series with the coil. If you use a relay rated for 12v you can jumper across this resistor.
Instructions for setting up the EMU are here: http://miatajoe.50megs.com/O2_Clamp.pdf
I've decided to stop building these, as it's more trouble for me than it's worth. As requested, I'm re-posting the schematic for my EMU-triggered O2 clamp here so that everyone can build their own if they want one. Perhaps some kind mod will sticky this so people can find it more easily in the future.
The resistor values are not absolutely critical. If you have to sub a 4.7k instead of a 4k it's no big deal- it'll just shift the centerpoint on the potentiometer a little. A note about the pot itself, I much prefer to use the more expensive box-shaped 15 or 20 turn units as opposed to the cheap single-turn units. You need a lot of precision when setting this resistor, and a multi-turn makes it a lot easier to set.
The diode across the relay can be damn near anything that isn't a Zener. I've been using 1N4004s simply because I have a pile of them. Use something that has a 1N400x number and you'll be fine.
The regulator probably doesn't need a heat-sink. It's only passing a few ma.
The trigger output of the EMU is 12v. Since I'd been using 5v relays (again, I had a few extras) I had to put a resistor in series with the coil. If you use a relay rated for 12v you can jumper across this resistor.
Instructions for setting up the EMU are here: http://miatajoe.50megs.com/O2_Clamp.pdf
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Thread Starter
Newb
Joined: Mar 2006
Posts: 5
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From: Fremont, CA
Quick question, might be dumb but I'll ask anyway...
Most modern cars have 2 oxygen sensors. Why do we clamp only one (1st / front). Is it the only one being used for closed loop fuel trim adjustment? What effect does the 2nd / rear O2 sensor have?
Most modern cars have 2 oxygen sensors. Why do we clamp only one (1st / front). Is it the only one being used for closed loop fuel trim adjustment? What effect does the 2nd / rear O2 sensor have?
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Joined: Sep 2005
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From: Chicago. (The less-murder part.)
Yup. it's one of those sensors whose sole job in life is to help you fail a smog check by throwing a CEL when it determines that the catalytic converter is no longer functioning efficiently of if its own heater goes out. Gotta love OBD-II.
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i got one of those clamps that joe built and the thing is flawless. worth the money i definitely would not be able to build on like that. sad to see you are not building them any more great product. 
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Senior Member
Joined: Apr 2011
Posts: 507
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From: Martin, Slovakia
https://www.miataturbo.net/e-manage-...ll-help-65812/
You can make one for < 10$ using a dpdt relay and a couple of 5k variable resistors.
You can make one for < 10$ using a dpdt relay and a couple of 5k variable resistors.
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