A/F Ratio Meter-Trying to make one in SHOP class...

A

agteacher

Life is GREAT!!
Joined
Dec 10, 2005
Me and my shop class students are TRYING to made a Air/Fuel Ratio Meter. I don't know if this will work or not, but we are going to try!!!! We are going to use 5 led lights each being .04 different from the last. The A/F(O2) middle led light will light at .76 to .80(best at WOT??? from what I have read..I think).....Does this sound like it will work. Reading would be like .66 to .90 OR do the reading need to be something else. We will pigg-back-off of the the narrow band stock 02 for our reading. I didn't not want to go to the wide band(cause my GN doesn't have one on it---and it didn't want to change it) One of my students' father is a "electronic wizard" or something. He is help with all the techno-stuff.

If those reading are incorrection PLEASE respond with Low--BEST--high.

I am hoping this will give us ANOTHER device to tune with, also we will be useing the boost,knock,fuel gauge,ScanMaster and WinALDL. Hopefully we will not blow-up the 1st time we tune.....
THANKS
 
I'm no expert but I will say tuning a car off a narrow band O2 or using it as a refference is a huge risk.
 
It will work but the resolution isn't that great. I would not use it to tune a car but you can use it as a reference. They make a driver chip (used in VU meters) that have a range from .1v to 1v in .1 volt increments that work quite well. You will have 10 led's for reference.
 
You can use an LM3914 IC to drive LEDs but be careful with the input. If you place too much of a load on the narrow band sensor, you'll skew the O2 millivolts and end up running too rich. The sensor is very sensitive and the ECM can be influenced by the slightest variation in the millivolt signal.

Standard O2 sensors aren't linear; the sensor will produce millivolts based upon oxygen present in the exhaust stream vs. oxygen in the atmosphere (the sensor uses reference oxygen obtained by sampling the air thru one of the wires) and the slope of millivolts vs oxygen is essentally flatlined in the stoichiometric zone...that's why you can't rely on it for AF calculations. Also, the sensor must be a minimum of about 900 deg. F to function properly (millivolt readings will be skewed downward if the sensor is below the operating temperature). This is why a heated oxygen sensor is desirable once you open up the exhaust system...much of the necessary heat is dissipated in better airflow, and the sensor produces a lower voltage than is necessary, resulting in a "rich" condition all the time.

Nevetheless, if you want to build a simple indicator of AF, the LM chip will do just fine. Be sure to use a sizeable resistor on the input to reduce the effect of voltage drop - the LM chip has a fairly high impedance input already.

Hope this helps.
 
RE-thinking

John
THANKS for the Great advise. I think we will rethink our approach to this activity. We will do as you advised and use the LM3914 IC, but I think that we will put a O2 in a ol'gas burner tractor :biggrin: and use it as our test vehicle/tractor. WE don't want to screw-up the GN.
How is the wiring harness going along for the Fans?
Thanks again for the "words for wisdon"
 
Off topic, but you asked about the plug and play harness. I'll have it by next week, actually two new designs for both F body fans and Spal fans.
 
Have you thought about along with the amplifier IC using a Analog to digital converter. This may provide a simple way to improve your resolution and go to a digital display. Of course this is not quit as simple as what you have in mind for a class project.

If you could get a wide band meter for a while you could set up a test jig with a torch and a pipe. One end of the pipe would be open and the other end fitted with the torch. On the end sealed with the torch you could drill holes that would allow you to control the oxygen flow. You need to contron the oxygen flow to the torch (propane). Assume a six foot pipe. About 3.5 feet up from the torch you could weld in two fittings,,,,,,,,,one for the wide band and one for the OEM sensor. With this you might be able to plot (rich to lean by controling the air inlet) the wide band against the OEM sensor/sensors (I am assuming a much higher resolution than you had in mind). I would guess each narrow band O2 sensor will read different from sensor to sensor and brand to brand. Each sensr would have its own table. Now within the narrow operational range of the OEM sensor you might be able to obtain some pretty good readings. Is it worth it?
 
Great activity...

Robert Kastle said:
Have you thought about along with the amplifier IC using a Analog to digital converter. This may provide a simple way to improve your resolution and go to a digital display. Of course this is not quit as simple as what you have in mind for a class project.

If you could get a wide band meter for a while you could set up a test jig with a torch and a pipe. One end of the pipe would be open and the other end fitted with the torch. On the end sealed with the torch you could drill holes that would allow you to control the oxygen flow. You need to contron the oxygen flow to the torch (propane). Assume a six foot pipe. About 3.5 feet up from the torch you could weld in two fittings,,,,,,,,,one for the wide band and one for the OEM sensor. With this you might be able to plot (rich to lean by controling the air inlet) the wide band against the OEM sensor/sensors (I am assuming a much higher resolution than you had in mind). I would guess each narrow band O2 sensor will read different from sensor to sensor and brand to brand. Each sensr would have its own table. Now within the narrow operational range of the OEM sensor you might be able to obtain some pretty good readings. Is it worth it?
Click to expand...

Great Idea....we will look into this tomorrow in shop class BUT 1st thing in the morning we are going to one of the local farmer to service his 3 tractors and hauling equip.....
THANKS
 
It looks like the site that Mike gave might be the best bet for a sure thing for a really nice meter. I am not able to get into all the links but it looks pretty nice and appears to be tested and in use by others ( big plus!! ). Yow could save a little money by using wire wrap instead of a printed circuit board. Wire wrap done right is quite good.

The post before Mike's would also work. The only thing I would do different is add a OP-AMP into the circuit. They can have very high gain along with a very high input resistance. As mentioned in another post this is important as to not cause problems with the ECM.

I have not done any circuit design in some time. I have been working in the power generation field designing engine and generator controls for large CAT diesels (1000-3000kW). My wife is a teacher and the last thing I would want to do is get something started that could not be completed on time.

There is a book that you migh be interested in. It is called the "Encyclopedia of Electronic Circuits", Volume 7. Rudolf F. Graf & William Sheets. This book is over a thousand pages of already designed circuits. It explains how to build all the cuircits along with how to make adjustments when needed. You do not need to be a engineer to understand it's contents. I think you would enjoy this book.
 
Thanks...to ALL

Robert Kastle said:
It looks like the site that Mike gave might be the best bet for a sure thing for a really nice meter. I am not able to get into all the links but it looks pretty nice and appears to be tested and in use by others ( big plus!! ). Yow could save a little money by using wire wrap instead of a printed circuit board. Wire wrap done right is quite good.

The post before Mike's would also work. The only thing I would do different is add a OP-AMP into the circuit. They can have very high gain along with a very high input resistance. As mentioned in another post this is important as to not cause problems with the ECM.

I have not done any circuit design in some time. I have been working in the power generation field designing engine and generator controls for large CAT diesels (1000-3000kW). My wife is a teacher and the last thing I would want to do is get something started that could not be completed on time.

There is a book that you migh be interested in. It is called the "Encyclopedia of Electronic Circuits", Volume 7. Rudolf F. Graf & William Sheets. This book is over a thousand pages of already designed circuits. It explains how to build all the cuircits along with how to make adjustments when needed. You do not need to be a engineer to understand it's contents. I think you would enjoy this book.
Click to expand...

Well...me and the class(s) started doing some research. 1st thing some of them ask was " are we going to blow-up another motor". I said "if you break it---this time-- you buy not me". So, now we are doing more research.
THANKS to ALL post.
I let my students read this site Every chance they get. They get a kick-out-of some of the posts and reseach for a answer before it is posted.(they feel like it is happening to their cars/trucks). Then, they argue with one-another on who was right!!!!
Again... Thanks for replying to our posts!!!!!
 
I think what you are doing is a good thing. Being a teacher that is! I am a little rusty. You just may get those kids addicted to learning. If you would like some help I could probably build some of the different styles of oxygen sensors and displays and email some prints. The wide band that Mike posted was nice but I dont know if I would want to spend that kind of money on a O2 sensor. I'm cheap and have had reasonable luck with my Scanmaster.
 
You can find a good article here for $4:

http://autospeed.drive.com.au/cms/A_3032/article.html

This company and the magazine they publish has a lot of electronics kits and info for boosted cars.

I bought the Smart air/Fuel display.

http://www.autospeed.com/cgi-bin/browse.cgi?category=579&product=1003707458&


It links the MAF signal with the O2 signal to determine the engine "load". I think its what you want and the kit is only $22. The instructions cover theory and they would be a good supplement to your project.

I haven't permanently installed it yet but I know it works well since its in a small project box hanging from below the dash.


Bob
 
You must log in or register to reply here.

Similar threads

B
2009 Nissan GTR Premium 35200mi Full Bolt on Mods $60,000
Replies
13
Views
1K
brian b
B
1
Trying to get back in a buick!
Replies
6
Views
598
Darkstar72
Darkstar72
S
Props to RCG
Replies
1
Views
1K
Cyclops389
C
M
RPS is offering 10% discounts to EVERY BUICK RACER THIS SEASON IN EVERY CLASS!!!
Replies
0
Views
708
marleyskater420
M
S
Digi-Tails LED kit
Replies
5
Views
2K
trixdout
T
Top