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Jack's O2 Mod

Page history last edited by MORG_kw 6 years, 7 months ago
Jack's O2 Sensor Mod
Now you're here and wondering just what this mod is all about, right? Well, have you noticed that when you ride your VStar 1300 at slow speeds in first or second gear that you seem to be getting a lot of surging? That's because Yamaha has the fuel mixture set excessively lean in order to pass the 2010 and 2012 emissions requirements. But, heck, it's not 2010 yet, let alone 2012. So why should I have to suffer for years? Well, you don't have to suffer. That's what this mod is all about. Not only will it eliminate most or all of the surging but it will also allow you to ride in higher (numbered) gears at slower speeds before you have to down-shift.
OK, so dude5 originally came up with the idea and gave it to me. That means, of course, that I did not steal it as he claims. How could I steal it if he gave it to me? I promised John (dude5) that I would not tell anyone about this and asked him if he planned to market it or post it on the WIKI. He said he was making his own FMS Fuel Management System that would sell for $100.00. He posted some pictures of a small black plastic box mounted on his handlebars. It has a couple switches and a knob on the outside. He was trying to find connectors that mate to the oxygen sensor. In the interim he had to cut and splice the wires.


Never mind all that history. However, if you look at dude’s FMS now, you’ll see he has added the O2 connectors that I told him where to buy.


The O2 sensor is a so-called narrow band sensor - like the ones in most cars. A narrow band O2 sensor can only tell you precisely whether you are above or below 14.7:1 AF ratio. That is its only purpose. You cannot measure whether you are at 12:1 or 13:1 or any other variation but 14.7:1 or if the ratio is lower or higher.


This is a very fundamental issue. Some other solutions use so-called wide band sensors that measure ranges up to 10:1-18:1 in discrete increments.


Why is this important to this story you may ask?


It turns out 14.7:1 is the most efficient AF ratio for various engine designs based on fuel consumption and emissions - not so in terms of power. The best AF ratio for these types of engines is usually around 13:1 +- 0.2 up or down.


As said earlier the O2 sensor can only be used for the 14.7:1 identification.


Now let’s have a look at a typical Yamaha FI map (very much the same as all other motorcycle manufacturers). The map has various AF ratios built into it. While cruising (usually below 10-20% throttle or less and less than a specific RPM e.g. 5000), maximum fuel efficiency (sounds funny when said in the context of a VMax) is the target - among best possible emissions. This is where the engine is mapped to a ratio of 14.7:1. It is this range and this range only that the O2 sensor data is used by the ECU to correct the AF ratio as it goes.


The primary reason for that is because gasoline based fuels burn hotter when you go over 14.7:1, and the increase in exhaust gas temps is dramatic and can lead to serious engine damage within a short amount of time. Of course, the 1300 is water cooled so that pretty well mitigates the heat issue.


For all the other ranges (>20% throttle and higher RPM) the manufacturers are not bound to emissions as much and therefore tune the engine for maximum power - which happens to be around 13:1. This is the range where the Yamaha ECU operates in 'open loop' mode. It has a map built in, it uses various air and vacuum sensors to correct the map for altitude and temperature but that's it.


In addition the Yamaha ECU (same for Stratoliner, Roadliner, Raider, and the sport bikes) can be operated without an O2 sensor. It goes back to a default mode without trying to optimize for the 14.7:1 ratio.


What the following mod does is to move the output of the O2 sensor to a slightly richer than 14.7:1 ratio. This cures the over-lean condition. The ECU “thinks” it’s running at a 14.7:1 ratio when, in reality, we have moved the ratio to a slightly lower value somewhere closer towards the 14.1:1 range, and the change made is enough to make a noticeable difference.


Now for the mod itself. As some of you have already figured out (and some of the units I did not seal with potting compound so an enterprising individual could easily open it and see what’s inside), the “circuit” is nothing but a single resistor. The resistor is in series with the ground lead of the oxygen sensor. The trick is the value of the resistor and exactly which wire to put it in. I chose to use resistors with a value tolerance of 1% but cheaper 5% tolerance resistors should work just fine.


Let’s look at dude’s version below. You’ll see he has a resistor with some shrink sleeving over it to prevent its being shorted to the bike’s frame. On the end of each lead is a crimp on connector. You simply find the sensor’s ground lead, cut it, and crimp the two connectors, one onto each lead that was cut. The pliers show how to crimp the connectors.
Since he was not going to publish or market the mod, I decided to tell everyone how to do it. Then I remembered my promise. That, and the fact that you have to cut and solder wires, made me decide to try and make some available myself. I built a prototype and sold it to kapu7 for what I thought might be a fair price, $30.00. Kapu suggested that $50.00 would be more appropriate so it didn’t look like a cheap something that doesn’t work. He even suggested I might want to ask even more than $50.00. That’s how the price came about.
My mod is shown below dude's. Notice that it is plug and play. You do not have to void your warranty to install it. Besides, it is very simple to disconnect for those occasions when you want to be EPA legal.
That’s just great you say, but what’s the value of the resistor and which wire do I have to cut? Looking at the O2 sensor connector (the one attached to the sensor) you can see two black wires, a white wire, and a blue wire inside some black sleeving. The white wire is the one you want. It connects to a black and blue wire in the mating connector. You can cut and use either the white wire or the black/blue wire. For anyone who is interested, you can find connectors available at www.EasternBeaver.com
My resistors are 825K ohms, 1%, ¼ watt precision resistors. I have several left. If you’d like one, send me a SASE (self-addressed stamped envelope) and a dime (pre 1964 is preferred) and I’ll send you one. Yes, I’ll lose about five cents each but there are no 15 cent coins that I’m aware of. 
Looking again at dude’s device, it looks like he has the connectors directly connected to resistor leads. I don’t think that’s a good idea. The resistor and its leads are too fragile. I mounted the resistor on a circuit board and soldered stranded wire leads to it. Then I put shrink sleeve over it and potted the whole thing. Of course, I used connectors that mate directly to the connectors on the bike so no cut or solder is necessary.
You could use a piece of a popsicle stick. Drill two holes in the stick 0.3” to 0.5” apart and pass the resistor leads through the holes. Then solder stranded wire leads (20, 22, or 24 gauge wire) to each resistor lead protruding from the stick. Finally, cover it with shrink sleeving or a good quality electrical tape to strengthen and protect it from shorting (dude, you can use this idea, too). Then either solder or use some of the "bullet" connectors to connect it.
JackK, K5TGJ
SIDE NOTE -- NOT to be overlooked - a highly appropriate friendly reminder from MaiKai:

If you do install Jack's O2 Sensor Mod (takes 10-15 min), once completed, rather than immediately starting the bike and enjoying a nice ride, it is often much better to first disconnect one of the battery terminals for a few minutes and then reconnect it (good time to add some dielectric grease to the terminals).  Doing this will allow the ECU--electronic control unit--to better recognize the change(s) made and recalibrate itself accordingly.  This same simple and effective procedure also applies anytime one adds or disconnects any type of a fuel controller type of device which alters even slighty the engine's air/fuel ratio.   

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