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Discussion Starter · #1 ·
Hi,
I have changed on my VN 900 Custom the EU stock exhaust for Cobra, the latter however does not have O2 plug as the stock one. As a result my FI is constantly "on". Insolentminx advised me that if I close the connection by plugging in 330 ohm resistor this will cheat the O2 system 9he has done the same).

However he does not know what was the type of the resistor.

So if anybody can help me I would be very greatful.

I have available the following types of resistors:

330 ohm/0.125W
330 ohm/0.25W
330 ohm/0.5W
330 ohm/2W
 

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Vicrory is Mine
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Duno.... I would think the ½ watt would be fine for just fooling the bike into thinking the O2 sensor is there.

P = (V X V) / R
P = (12 X 12) / 330 = .4363636
P = (13 X 13) / 330 = .5121212
P = (14 X 14) / 330 = .5939393
 

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Discussion Starter · #5 ·
Thanks Vulcan900! As I am not very familiar with the electrical part this is very useful.
However do you think that the fact than on the move the battery is charged to 14 V will influence the resistor (P = (14 X 14) / 330 = .5939393).
 

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Vicrory is Mine
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I think you would still be fine. Worst case failure would be an open circuit if the resistor overheated. Put it on and go for a ride. See how hot it gets. If you can touch it without discomfort after an hour ridding you are good. If not, go up in wattage. Remember, resistors create heat when current passes throug them and that heat needs to go somewhere. If you wrap it up in a ball of tape you are keeping the heat in.
 

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I believe you've listed the power ratings of various resistors - how much power they can dissipate while doing their thing.

Per the above power computations the 1/2W may do fine but why not just use the 2W?
 

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Discussion Starter · #11 ·
Guys, don't fight over the issue. The resistors are available in the local store. But as I am not specialist I preffered to ask the peaople that know more then me,i.e. you. I got very useful info from Vulcan900. I will check the actual size of 2w resistors and as I need two if they fit in the confined space there I will put them to be on the safe side, otherwise I will go with 0,5 w.
In any case I will give you a feedback.

Thanks once again
 

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I don't think we're fighting ... but yeah, I do tend to be very brief in my posts.

I think you'll find the differing cost and size to be ... a non-issue. Remember what Vulcan900 said about not wrapping them up. Just insulate the wires, not the resistor 'casing.'
 

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Vicrory is Mine
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Numbers and calcs are worst case. You probably only need a 1/8W resistor anyway. The ECU is monitoring the O2 sensor. Probably not the full 12+- volts and probably not applied 100% of the time. A few measurements with a meter would confirm my suspicions.

Sorry for the spelling I'm on my phone.
 

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Discussion Starter · #16 ·
"I would think that using the O2 sensor would work better than a fixed resistor."

O2 sensor means ruinning my cobra exhaust as it must be welded there and they do sell O2 eliminators but at cost of $$$ plus the delivery to EU. Against 330 costing less than 1 $. Insolentminx installed 330 resistor since thousands of miles with no issues (unfortunately does not remember the "w" as the resistor was supplied to him by another guy and he lost the contact).
 

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Discussion Starter · #18 ·
"How would welding in a fitting ruin your exhaust? Mount it in an out of view location and move on"

Very easy, they do not build custom bikes arround and no body has enough knowledge to let him arround the exhaust. Apart the sensor actually must be cut from the old exhaust, the new one must be then cut in turn and the sensor welded. The stock exhaust has EU standard anti-polution system against none in the cobra, so who can tell you how the sensor will react.

So I am going with the foolprof and tested solution.
 

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The amount of heat dissipated by the resistor is going to be roughly the same regardless of whether you use a 1/8 watt, 1/4 watt, 1/2 watt or 2 watt resistor. If you are putting 1/8 of a watt through the 2 watt resistor, you're going to get 1/8 watt worth of heat. If you put 2 watts through the 1/8 watt resistor, it's going to burn up/short out.

The moral is you can always use a larger wattage resistor, but you can't use one smaller than your load. I'd recommend trying to find a flame-proof resistor, too, so that if you start out with one that is too small it won't flare up on you.

Vulcan900 is correct that you probably won't need to worry about carrying a full 14 VDC (or even 12 VDC) load through the contacts that used to connect to the old O2 sensor. But the resistor does need to be sized for worst case, even if the load is not applied 100% of the time.
 
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