Pagoda SL Group
W113 Pagoda SL Group => Drive train, fuel, suspension, steering & brakes => Topic started by: Cees Klumper on September 08, 2013, 18:20:20
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In various forums covering one of my favorite hobbies (cars and motorcycles) I have noticed the "02 sensor phenomenon" and it seems to be beneficial for tuning / fuel/air adjustment purposes. Requires inserting a sensor into the exhaust system?
I know I can educate myself via the net, but since this is a topic that would probably be of interest to others as well, I am starting a new topic to learn about this.
Can anyone post a "02 sensors for dummies" here?
Thanks!
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Cees,
If you don't have it already, you should add the following book to your library:
http://www.amazon.com/Bosch-Automotive-Handbook-8th-Edition/dp/0837616867
I have the 6th edition (but it was free so I'm not complaining... ;)). While the specifics of oxygen sensors are small, nearly any topic of anything to do with automobiles is covered in some fashion in this book, thus is a good reference for those that don't like, um, er, wikipedia. BTW, Bosch invented the oxygen sensor. I have a note into my friends there to see if there are any in-depth documents they can share.
I would not be surprised if they have the book in other languages, but I know your English is 99.99%. Most Americans are at about 95%.
I know what you REALLY want, but alas it's still in production...just the cover is complete. :D
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All modern production cars have an O2 sensor in the exhaust.
Basically an O2 sensor is a battery that produces a voltage when exposed to oxygen.
Oxygen is present in the exhaust system of any internal combustion engine and the amount of oxygen present is a factor of the fuel/air ratio being burnt.
Everyone knows that the correct Stoichiometric ratio is 14.1 parts air to 1 part fuel and it is this ratio that you are adjusting when twiddling the knurled knob on the back of your injection pump.
Now, the o2 sensor in your modern car is known as a "narrow band" sensor because the air fuel ratio is carefully metered by very modern equipment and so deviations from stoichiometric perfection are small and therefore the voltage variations produced by the sensor will be correspondingly small. (About 1v range). So, when your modern EFI is working correctly the voltage that is generated by the sensor will be fluctuating between +0.5V and -O.5V. This fluctuation is a result of the ECU constantly reading the sensor voltage and making corrections to the fuel volume injected in order to keep the voltage at an average of 0V.
This narrow range is fine for modern EFI cars, but is no good for tuning application where a wider range of mixtures might be expected or desired so there is a "wide band" O2 sensor which operates over a range of about 6V that can be used in more "abnormal" situations like those found on our cars.
Since our cars were not fitted with O2 sensors when new we must install a fitting so that we can insert one. These threaded fittings are commonly available from most tune-up suppliers along with a blanking plug to close the hole up afterwards.
There is a fair amount of information on this site about how to fine-tune your injection pump and this information used in conjunction with a wide band O2 sensor will yield excellent results if patience is combined with a methodical approach.
So, you cut a hole in your exhaust downpipe and weld in the threaded insert. (There are other ways but weld-in is best). You then install a wide band O2 sensor and run a cable from it into the inside of your car. (Through the window is fine as you'll be removing it later). You connect this cable to a display which you temporarily affix inside the car.
Using this display you will drive and tune, drive and tune, drive and tune until you get as close to 14.1 on the display as possible under normal warm conditions and anywhere between 11 and 14.1 when cold or under full load. (lower is rich, higher is lean). The only time lean is acceptable is on over-run. In reality you'll be happy with 14.5 or 13.7. Naturally, you will then want to check that you are getting enriched mixture when cold but you must establish the correct setting when warm first.
Once you are satisfied you simply remove the display, cable and sensor, install a blanking plug into the threaded insert and enjoy!
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Thanks a million, Michael and Colin - all set now. So I will be getting me one of them wide band sensors and get to work...
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Cees, I do have some stuff coming to me from Bosch. I'll PM to you when it comes, if you think it worthy, you can repost it.
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Interesting thread. Thanks, guys.
Colin, my heart jumped into my throat when I read "Through the window is fine. . ." I think you meant "through the OPEN window. . ." :-[
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I always thought for gasoline the ideal ratio is 14.7/1. I have an Innovate wide band sensor. You can buy an attachment to clamp it to your exhaust pipe. I have this as I use it on more than one car and it's easy to install remove. http://www.innovatemotorsports.com/products/lm2.php (http://www.innovatemotorsports.com/products/lm2.php)
http://www.innovatemotorsports.com/xcart/product.php?productid=16141&cat=271&page=1
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Yes, 14.7:1, this is what I thought also. Isn't the knob at the back of the injection pump for idle only? I remember on my 6.3 I had to go in with a small screw driver via the back of the pump to act on the rack. Also, ignition advance timing can greatly influence the air to fuel ratio. The more advance, the leaner in burns.
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Yes the out side knob is Idle range gas. The low end partial and high end partial are on the govenor behind the idle gas knob.
http://www.sl113.org/wiki/Fuel/Injection. The screws are not labeled correctly: the Full Range is the rack screw for top end full load, which really means full load and any end: top, middle or low. The white screws are "Top End Partial" the black sdcrews are "Bottom End Partial."