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Mixture Control

Modern vehicles use an oxygen sensor in the exhaust system to tell the computer just how much fuel to inject each cycle. When the combustion process is improved by proper vaporization of the fuel, then the exhaust oxygen content will rise. This might sound contradictory and you may expect that the more complete combustion would use up more oxygen. The opposite is what happens in reality. Less nitrogen oxides are produced and this means more free oxygen. Gasoline is predominately carbon and hydrogen. The exhaust products are a mixture of carbon monoxide, carbon dioxide, water, unburned hydrocarbon molecules, oxygen, nitrogen and oxides of nitrogen. As well as all the other nasty additives that are included in fuel these days. The catalytic converter is used to complete the process and thus reduce pollution. Additional air is added prior to the converter to enable it to function. How does the oxygen sensor work Nearly all automotive sensors are of the zirconia type. A ceramic bulb projects into the hot exhaust gas. The bulb is hollow and the inside surface is in contact with the atmosphere outside the exhaust pipe. Both surfaces are coated with platinum. Oxygen atoms are negatively charged and will attach to the platinum surfaces therefore building up a negative charge on each surface. When the hot exhaust contains little or no free oxygen then the charge on the bulb surface will be less than on the other surface. A voltage difference is produced and electrodes attach to each surface. The atmosphere side is connected to the vehicle earth, so the other side will be actually a positive going voltage since it has less negative oxygen atoms. It effectively forms a battery that only works once it has reached several hundred degrees, and the output voltage is dependent on the oxygen concentration of the exhaust gas. From the Sensor Graph you can see that the output is not linear and actually changes abruptly about the stoichometric point. This is the point where the air/fuel ratio is optimum at 14.7 : 1 and should result in total combustion. Lean conditions give close to zero volts out and a rich mixture will produce about 1 volt maximum. A very small change in the air/fuel ratio about the mid point will cause a large change in the sensor output. The computer can't always maintain a perfect mixture to keep the output exactly in the middle, so instead attempts to only maintain the average at that point. The sensor output will oscillate while driving. The rate of oscillation will vary according to how fast the sensor can react and how fast the computer reacts. Typically the rate is anywhere between 1 and 10 cycles per second.

The computer has 2 main modes of operation, open loop and closed loop. In open loop mode the oxygen sensor is ignored, with all the other sensors being used to calculate the required fuel quantity. Throttle position, air flow rate, air temperature, engine speed and others are measured and used for calculation. The calculation is quite accurate only if all the sensors are accurately adjusted, so adjustments of these is best left to the experts. The computer operates in open loop mode, ignoring the oxygen sensor when it suspects the sensor is not working. Remember the sensor must be hot to work so after start up the computer is waiting to see the sensor output go high first before it will change to closed loop mode. In this mode the other sensors are still used to make the main calculation, but the result is modified slightly according to the sensor output. Some computers learn as they go and are able to calculate a more accurate fuel requirement faster. There are other times also when the oxygen sensor is ignored. When accelerating hard with the throttle beyond about three quarters open, the mixture will be set rich to provide more power. When coasting down from high speed the mixture will go lean. If you install a dash mounted mixture display you can see this happen as you drive. We recommend this display because it helps tremendously to see exactly what the oxygen sensor is putting out at all times. MIXTURE GRAPH The Mixture graph displays the relationship between power, economy and air/fuel ratio. To control your mixture as you drive, it is a simple matter of intercepting the oxygen sensor output before it reaches the computer and offsetting the signal slightly. You can adjust for leaner more economical driving or even richer mixture giving greater power. Using our Electronic mixture controller you have the ability to alter your air/fuel ratio as you drive. It is completely automatic in operation and the car can be driven normally. This is essential in a vehicle that will be driven by others as well as yourself. If you apply any mileage improving devices to a fuel injected vehicle, it is essential to also install the Electronic Mixture Controller to fully realize the gains available. Our controller has the additional benefit that it can speed up the reaction time of a particularly sluggish sensor. Even simple water or steam injection will increase the exhaust oxygen which the computer will attempt to compensate for. It is possible that water injection could result in worse mileage if you don't electronically fool the computer.

Vapor Systems We have developed a practical vapor system, involving adding fuel and additional air to the PCV hose. There are problems to be overcome in such a system. The main obstacle is getting the engine to idle properly. You need to add enough fuel to make a difference at cruising speed, yet not cause it to idle excessively high. You also need to add the correct ratio of fuel and air to get the best gains. We have found that a mixture display is essential to adjust the system. This system has resulted in an immediate 10% mileage gain. This is on top of the 18% resulting from the steam injection and mixture controller. DANGERS Remember a lean condition is potentially damaging, and a rich mixture can very quickly heat up your catalytic converter. This can destroy your converter or worse still, cause a fire under the car. Leaking fuel is always hazardous, so use quality parts and check all connections. Always use hose clamps on fuel line, don't simply rely on tight fitting hoses. SYSTEM SETUP

Our system is incorporated into the existing PCV add ons described previously. A 'T' piece is installed in the PCV hose close to the steam inlet, between it and the inlet manifold. To this is connected our cold vapor system. Any unvaporized fuel reaching this point will then encounter hot steam, and have more chance of fully vaporizing before the inlet manifold. The vapor hose is about 2 feet long, 3/8th inside diameter. There is another 2 feet of hose after the 'T' before the manifold. The amount of air is regulated by a metering orifice close to the connector. Fuel is admitted at another 'T' close to the open end. The fuel flow rate is controlled by a simple restriction in the fuel line. We use a short length of copper tube to join the fuel line, with it's ends flattenned. Trial and error in the flattenning is used to adjust the flow to the desired rate. Only a tiny hole is needed. In carburettor vehicles, tap into the fuel line just before the carb. In EFI vehicles, tap into the fuel return line. The main fuel line has way too much pressure. We found it essential to use a fuel solenoid to turn off the fuel when the engine is off.

It was also essential to turn off both the fuel and the air at idle. The amount of air and fuel that is necessary to make a difference at highway speeds, is too much to allow for normal idle revs. We have designed an electronic controller that does this. It also has a dash board indicator to show the functioning of the device. This controller also monitors the output of the mixture controller ( if installed, or the simple Mixture Display output can be used. This is shown on the previous page.) and cuts the fuel if a rich condition exists for a preset duration. •

NOTE * This system setup will only work if your PCV hose is connected to the manifold in a location that will distribute the vapor evenly to all the cylinders.

Electronic Mixture Control

If you have some electronics knowledge and experience then you can build this simple electronic device yourself, and unleash the full potential of any other high mileage system you choose to install. We provide all the information needed to build, adjust and install this fuel saving device. Shown here with the dash mounted LED display. New special price Free! Here is the link. You won't be charged so tell your friends. Sorry there is no email support, so please don't ask any technical questions. We are now relying on third party sponsors.

Electronic Mixture Controller Manual This is one long page and should print out without any problems. Saving this page won't automatically save the images so remember to save the images individually. HOW THE SYSTEM WORKS The car's computer is expecting to see an oscillating signal from the oxygen sensor which goes from zero volts to plus one volt approximately. The fuel flow is adjusted to maintain the average voltage at close to 0.5 volts The signal from the sensor isn't a square wave, but more like a smooth triangular wave form. The computer doesn't care about the exact shape but simply tries to maintain the average. The Electronic Mixture Controller is installed in the system between the oxygen sensor and the car's computer. What this device does is convert the wave form into a square wave, but more importantly it sets up a threshold voltage that is lower than 0.5 volts. When the sensor output is above the threshold, which is set quite low, say 0.1 volts, then the device will send a high signal to the computer. When the sensor signal drops below the threshold the device signal out will be low. The computer adjusts the fuel flow accordingly and now is actually maintaining the average voltage from the sensor at 0.1 Volts (100mV) instead of 0.5 volts. (500mV) From the Sensor Output graph you can see that the mixture is now slightly leaner than it was. The operating range is shifted to the right. We have cut the fuel quantity by no more than few percent, perhaps 5 %. This by itself will produce some mileage improvement but not a lot. The greatest benefit occurs when applying the device in support of some other high mileage system. Especially cold vapor systems and water injection. The computer will normally fight these systems to compensate for the added

exhaust oxygen. This device fools the computer and enables the maximum possible mileage improvements. If your oxygen sensor is old and sluggish this device will also improve the reaction time. Because it instantly tells the computer when the sensor output is below or above the threshold, there is less overshoot. Smaller, quicker corrections to the mixture occur rather than long slow corrections. CIRCUIT DESCRIPTION The heart of the circuit is the LM3914 linear LED dot/bar Driver IC, which we operate in bar mode. This is the same IC as is in the Mixture Display circuit. We set the sensitivity to 500mV full scale for this controller. If you want to be able to adjust your mixture richer for more power rather than leaner then you should adjust the sensitivity to a greater voltage, around 700mV. It is not recommended to set the threshold too high, because it is quite possible that your sensor output may never reach that high. The computer will keep adding fuel expecting the signal to go high. Remember, excess fuel will be burnt inside the catalytic converter which could cause a meltdown. Don't risk a fire under your seat. Or it may simply ignore the sensor and operate in open loop mode. Electronic Mixture Controller Circuit Diagram

WARNING This is a static sensitive device. Handle it carefully and always use an IC socket to mount it. Don't directly solder the IC into the printed circuit board. Install this component last. We use this IC to sample the sensor voltage and provide outputs at various thresholds that we can select from. The trim pot R1 sets the sensitivity and we adjust this for 500 mV full scale. Each LED output then is 50 mV apart. We don't actually install LED's on each output, and any

unused outputs are left open circuit. The front panel rotary switch selects which ever output we choose. We only need 2 or 3 to choose from. You can leave out this rotary switch and simply select one of the outputs to connect if you prefer. The front panel on/off switch is a DPDT toggle switch. All the capacitors are electrolytic type of about 16 volt rating. All resistors are 1/4 watt. The input resistor/capacitor circuit provides filtering of the sensor signal. Because the entire circuit comprises high impedance components, including the sensor and IC input, the input line is susceptible to induced noise. Ignition noise in particular will affect the circuit and cause incorrect operation. If you install the LED Mixture Display as recommended, you will see that until the sensor heats up all the LED's will be dimly lit. This is showing that there is a lot of noise on the line. When the sensor heats up, the signal becomes cleaner and then only the appropriate LED will be lit. We also include a delay circuit so that after start up, the output is held low for a few minutes to simulate a cold sensor. The sensor must be operating correctly before we send signals to the computer. The most common problem, if we don't have this delay, is that the output will be high simply from the noise on the signal line. The computer will think the sensor is working, because it is high, and will cut back the fuel to make the signal go low. When this happens we end up with a very lean condition and very poor acceleration. The front panel switch is very important. It doesn't switch the power to the device. What it does is allow the sensor signal to bypass the device altogether. This is an essential feature. You can switch your vehicle back to it's unmodified state instantly if you suspect that there may be a problem with the device or if the vehicle simply isn't performing as it should. Remember, only you know what you have done to your car and other family members that drive the car may not be able to fix any problems that may arise. Just show them the switch. The front panel LED is not just to show that the device is operating, but forms a simple voltage regulator for the output signal to the computer. In operation the LED is lit when the output is high. So the correct state for the LED to be in is flashing. BEFORE BEGINNING This is a simple test you should perform first. The oxygen sensor earth connection is the exhaust system, which is firmly bolted to the engine. The computer earth is the vehicle body. We have seen that 0.5 volts can make a large difference to the mixture. If the engine is not well and truelly earthed to the body then a voltage difference can exist between the two, and 0.5 volts would normally go unnoticed. We can't afford to have that sort of voltage difference when trying to accurately control the mixture. Start the engine, switch the headlights on high beam, then measure the voltage between the engine and the body. Use an accurate digital volt meter. Any more than 50 mV will mean you have a bad earth connection which will need cleaning and tightening. Modern cars usually have more than one connection so look around. If you have trouble achieving this then use an engine earth connection for you circuit rather than a body connection. What is most important is the signal voltage from the sensor, since we are operating at such low voltages. PARTS LIST

IC LM3914 linear LED dot/bar Driver IC Transistor BC 327 pnp general purpose Darlington Transistor MPSA14 npn high gain darlington Diodes 2 x 1N4007 or equivalent LED 5mm round, any color Trimpots 2 x 10K linear carbon Capacitors 3 x Electrolytic 10uF, 0.1uF, 2.2uF Resistors carbon film 1/4 watt 1 x 10M 2 x 1M 1 x 3.9M 1 x 10K 1 x 2.7K 2 x 1K Rotary switch single pole Toggle switch DPDT Printed circuit board general experimenters board about 2 x 3 inches Case to fit

CONSTRUCTION Read this through completely before beginning. All the parts needed should be available from your local Radio Shack store. They will also be able to show you the component orientation and which legs are which etc. You will require a soldering iron, a 12 volt power supply such as a small power pack and an accurate digital volt meter for this project. No other test equipment will be needed. The 12 volt supply should be well filtered. You want proper DC, not simple rectified AC, which contains too much ripple. Lastly you will require a variable voltage source that can go from 0 to 1 volt to simulate a sensor input. It's simple enough to make this using a resistor and a variable resistor. The transistors are nothing special, just general purpose devices so it should be OK to substitute where necessary. The darlington transistor (MPSA14) is a special high gain device needed for the delay circuit. Again it is just a general purpose darlington transistor. The printed circuit board can be any general experimenters board approximately 2 x 3 inches. Try to plan ahead and think where you are going to mount the device, either behind the dash or in a small case mounted somewhere. The printed circuit board has to fit and after the components are mounted it will be more difficult to fit in a tight location. Start with the IC socket, and mount it slightly in from one end. The circuit diagram can give an indication of the general layout of the components. It makes it easier to follow the circuit if the components are in the same position as on the diagram. You will have to decide for yourself where and how you mount the front panel components, the rotary switch, the on/off switch and the LED indicator. The IC legs are numbered 1 to 9, left to right across the bottom as seen on the diagram, and 10 to 18, right to left across the top. The notch shows the left end, this is standard for all IC's. Try to plan the component positions so that you require the least amount of additional wire to make all the connections on the board.

Don't connect the wires to the front panel rotary switch just yet, except for one which connects to pin 10 on the IC. This is the full scale output and will be connected to the rotary switch in the position of FULL RICH, whichever you prefer, fully clockwise or anti-clockwise position. You are going to test you device first on the bench, then decide which outputs you will use for the other switch positions. Don't install the delay capacitor C3 yet. Don't install the IC yet. Now install all the other components and double check every single solder connection. Check the quality of the joints and check that the circuit complies with the circuit diagram. Before installing the IC you can apply power to the circuit to check for any overheating components. The circuit has been designed such that none of the components will get even slightly warm in operation. If any parts do get excessively hot then there is a problem. With the IC not installed the output transistor should be off, and the output LED off. The darlington transistor should be off because the capacitor is not installed. ADJUSTING ON THE BENCH Disconnect the power before installing the IC. You can now install the IC, the correct way round or it will be destroyed instantly. Apply 12 V power to the device. Set up the test voltage source to 0.5 volts and apply to the input. Set the switch to the FULL RICH position. Now adjust the sensitivity control trimpot VR1 so that the output LED is just lit. Leave the trimpot alone and now adjust the test voltage lower then higher to test the adjustment. The LED should come on at 0.5 volts, and go off just below 0.5 volts. You can measure the voltage on the other output legs and see when each goes on and off. They will be zero volts when on and some very vague voltage when off. The outputs will even sometimes go negative when they are off. We suspect it is something to do with the high impedance outputs rectifying the ripple on the DC supply. All the outputs should be about 50mV apart in their threshold points. With the output high, (LED lit) adjust now the output voltage to the computer by adjusting the trimpot VR2. You want to set the output to 1.0 volts. Adjust the test voltage to below the threshold to turn off the LED. The output voltage should be zero volts. If all the above happens as it should then your circuit is working correctly. Next install the delay capacitor C3. Set the test voltage above 0.5 volts and turn the power on. It should take about 30 - 120 seconds before the LED comes on. You can adjust the delay by changing the value of the 3.9M timing resistor and/or 2.2uF capacitor. If you find the oxygen sensor heats up quickly then set the timer to a lesser value. Having too long a delay is bad, since the computer could be adding extra fuel to try and make the mixture rich.

The next task is to select which other outputs you want to use, and connect these to the front panel rotary switch. We recommend you use 100mV or 150mV as your lowest output, depending on what other high mileage devices you use. If you want you can alter the sensitivity to say 400mV full scale to make available settings like 80 or 120mV. Thoroughly test the device on the bench to be certain it functions as it should. When you first install the device in you vehicle, use a setting near to 500mV to test the operation of the device. Your performance should be completely normal. Drive like this for a while to prove the system is working reliably before changing to lower settings. TESTING IN THE CAR You can now test the device in the car. Don't install it yet though. Lift the hood and locate the oxygen sensor. Don't cut the sensor wire. Find a convenient place along the wire where you can strip back some of the insulation. You are going to cut it here later, but not yet. Connect this point to the input of your mixture controller and attach the power leads to the battery. Start the car and allow the sensor to warm up. Remember there is a delay built in so after a few minutes you should see the LED start to flash. Rev the engine and the LED will stay on. When you release the throttle, the LED will go out for a while. A flashing LED is what you want to see. The rate of flashing will be somewhere between 1 and 10 times per second, most likely around 2 per second. Check that the LED goes out when you switch the front panel switch off. Now comes the exciting bit, cutting the oxygen sensor wire and inserting the controller. Cut the wire in a convenient place. You are going to use crimp connectors to finish the installation. Use a matching set on the wire you just cut, in case you need to reconnect it back together. Don't drive the car yet, do this test in the driveway. With the front panel switch off, start the car and check it runs normally. Set the front panel rotary switch to the FULL RICH position.(the position connected to the last LED output, 500mV) and switch the device on. The car is now running with a modified oxygen sensor signal although the mixture is still the same. Try the other positions in order and see how it runs. INSTALL THE CONTROLLER Fit the controller to the vehicle and finish hooking up the wiring. For the 12 volt supply find a connection which is switched with the vehicle ignition. You don't want to have to turn it off every time you stop. Return to the FULL RICH setting and road test the car. Drive a few miles at each setting to see how it performs. If you have also installed the Dash Mounted Mixture Display you can also see at which level your output LED comes on. It is very reassuring to see the actual sensor output displayed in real time, and to see the Electronic Mixture Controller actually make a difference to the sensor output. IMPORTANT

Only connect the display input to the raw sensor output, not the controller output. The display is independant of the controller, and is not switched off when the controller is switched off. We can at all times see on the display what the sensor is putting out. The controller doesn't directly change the sensor output, it fools the computer into cutting back the fuel. It is up to you to decide which setting you will use for normal driving. If you have not installed any other high mileage device or water injection then you should be conservative in your adjustment. We have installed water injection only and are driving on a setting around 240mV. We believe it is close to ideal at this setting. Mileage Gain Since installing this device and the steam injection our mileage has improved approximately 18%. This is in a vehicle that has always been serviced regularly and has driven over 150000 miles.(250000 kilometers) Good luck with your project and safe motoring.