O2 clamps for EMU - Miata Turbo Forum - Boost cars, acquire cats.

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Old 10-09-2007, 10:36 PM   #1
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Default O2 clamps for EMU

Based on recent discussion I've had a couple of requests to build O2 clamps similar to the one that I use in my car. The design of these is specific to the EMU in that they use the EMU's AUX output map as their trigger, rather then relying upon an external MAP sensor or switch. The advantage here is that you can scale your AUX Output map the same as your A/F Target map and I/J Adjust maps, and set the O2 clamp to only engage in cells where you are performing injector correction and / or wideband autotuning. This way there is no possibility of the clamp not being engaged in a cell you are trying to correct, or of it being engaged when you are not performing correction.

Pricing will be the same as Olderguy is charging for his non-EMU design. $70 shipped in the US, $75 elsewhere. These are going to be built to order, so expect a few days' lead time on shipments.
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Old 10-12-2007, 10:17 PM   #2
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so that price is fixed? i am not sure i can afford that much for the clamp now.
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Old 10-16-2007, 07:12 PM   #3
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Honestly, at that price I'm not making any money. I'm only offering these because several people asked about the one I built for myself.

The parts aren't terribly expensive, but these things take a while to assemble and test. I'm selling them for the same price that Olderguy asks for his non-EMU version, which is considerably less than FM charges for theirs and so far as I know this is the only design that integrates with the EMU.
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Old 10-16-2007, 09:34 PM   #4
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Can you make one for stock ecu?
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Old 10-17-2007, 12:05 AM   #5
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Quote:
Originally Posted by supra441979 View Post
Can you make one for stock ecu?
This particular design works with the stock ECU when an eManage Ultimate is also present. That's really the whole point of this design- that it uses the EMU's Auxiliary map as a trigger, rather than relying upon a pressure switch or a separate MAP sensor as all the others do. This way the O2 clamp is guaranteed to always be in sync with the EMU's injector correction and A/F target maps.

If you're not using an EMU, then I suggest you check out Olderguy's sticky thread in the ForSale section. His design uses a seperate pressure sensor, and is suitable for cars using an EMB or AFPR. I'm not going to compete with him on these since he was here first.
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Old 10-18-2007, 12:50 AM   #6
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Ben, I think it's cool that you are considering making them. The problem with little projects like these, is that the electrical goodies usually come in bulk so it's not cost effective to make just one.

I already have the o2 sensor wired to the EMU (Analog In/Out) so it looks like I could rewire it pretty easy. This seems to be a much improved method for clamping the O2.

Some questions:

1. Is it the same specs as olderguy's, only without the pressure switch? I have seen his schematic, but never seen the actual unit. I think he has a pot for adjustment and also an LED to indicate when it's intercepting the signal.

2. How's it packaged? Circuit board, box, or a bare rats nest?

3 How do I wire it in? Is it wired in with 4 wires like this:
-O2 wire to ECU
-O2 wire to Sensor
-EMU AUX Output
-Ground

4. What voltage does it output when on?
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Old 10-18-2007, 12:34 PM   #7
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Quote:
Originally Posted by retro View Post
1. Is it the same specs as olderguy's, only without the pressure switch? I have seen his schematic, but never seen the actual unit. I think he has a pot for adjustment and also an LED to indicate when it's intercepting the signal.
Well, there's only so many ways to describe how an O2 clamp works, but I'm using a completely different design. First, rather than relying upon the voltage drop across an LED as the reference voltage I am using a linear regulator. This is because the forward voltage of a diode changes very slightly with temperature, whereas linear regulators are internally compensated. The output of the regulator goes into a divider network consisting of an 8k fixed resistor, then a 2k 25-turn potentiometer, and to ground. The center tap of the pot feeds the N.O. contact of a microrelay. The stock O2 sensor feeds the N.C. contact, and the common goes out to the ECU. The relay is triggered by the Aux output line of the EMU.
Quote:
2. How's it packaged? Circuit board, box, or a bare rats nest?
I've been packaging them in little aluminum cases about 1.5" x 2.5". I wish I'd taken a picture of one... Five wires exit through a grommet on one side, and there's a hole on the other to adjust the trimpot which calibrates the output voltage. I have not provided any particular mounting provision on the box, since different Miatae have their ECUs in different places. On the underside you can see the four nuts retaining the circuitboard standoffs- this would be a good place to slip a mounting bracket in if you wish to fabricate one for your particular car. Otherwise it's small and light enough that you can just tie-wrap it to the wiring loom that feeds the ECU.
Quote:
3 How do I wire it in? Is it wired in with 4 wires like this:
-O2 wire to ECU
-O2 wire to Sensor
-EMU AUX Output
-Ground
Yes, plus a fifth wire to supply +12V. I power the regulator separately rather than driving it off the EMU's Aux Out. This helps to ensure stability.

Quote:
4. What voltage does it output when on?
It's adjustable- anywhere from 0 volts to about a volt or so. By default, I pre-set them to 370mv, and provide instructions for adjusting.

Here is a link to the documentation for the device: http://miatajoe.50megs.com/O2Clamp/O2_Clamp.pdf
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Old 01-24-2008, 12:13 PM   #8
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Well, in the three months since I shipped a whole three clamps. At this rate it's really more trouble for me to build these things than it's worth.

Schematic and instructions posted at the link below so everyone can build their own.
https://www.miataturbo.net/forum/sho...d=1#post204086
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Old 01-24-2008, 01:42 PM   #9
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Question on the 02 clamp. I have a MSM and have installed an 02 clamp from Flying miata. It works fairly well. I recently installed an EMU. I have the 02 clamp still installed in the recommended location from FM. Should the FM 02 clamp work in it's current configuration and the EMU just recieve the modified signal from the factoy ECU? or, would I be better suited to try and figure out how to wire it into the EMU?
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Old 01-24-2008, 02:34 PM   #10
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The O2 clamp stays where it is- the whole point is for it to trick the factory ECU. The EMU is typically not even connected to the NB O2 sensor.

We just want the factory ECU to not realize that the EMU is deliberately richening the mixture when transitioning into boost.
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