I've seen a bunch of posts about testing your air/fuel mixture.

Is this something you can do at home? Is there some sort of tester you can buy that will let you adjust this? If so, how does it work?

Sorry for the silly question..


[Modified by Corellian Corvette, 1:54 AM 3/25/2002]

 

You can buy an oxygen sensor and use a standard voltmeter for it. If I remember right, the scale winds up with max power (rich) being at .875V. You want to be over .500V for sure.

Just weld the sensor in your pipe right under the manifold, and attach a positive lead to it and the voltmeter, and ground to the chassis. Boom, instant tuning info.

Or, you could go slightly more expensive and buy a gauge that reads the info for you and displays it in pretty colors. Red = LEAN, Yellow = good mix, Green = rich; this is on my AutoMeter gauge.

 

I took my 75 to Carb Connection and got a dyno and air/fuel mixture at the same time...they will give you several runs so you can make some adjustments between runs; for example, tweek secondary rods, and/or replace jets, modify timing, etc.

 

My car has an oxygen sensor. So, if I buy an oxygen sensor, cut off the plug and solder on 2 wires, 1 for 12volt+ and one for positive lead to the multimeter, then put my multimeter on volts, I should have all I need, correct? If so it sounds like I need to get another oxygen sensor. :D

 

So it's an Oxygen sensor that's used? I always see posts about 13:1 air/fuel (or something similar). How do you test for those readings?

 

anyone?

 

The easiest way to go is to buy a kit with a meter and sensor. K&N, Edelbrock and Autometer sell them (www.Jegs.com or http://www.summitracing.com). They display a range from about 11.5 or 12 to 15.5 or 16 and are about $150. I've never used a volt meter, it might be a little difficult but it would be cheap.

Jeg's p/n's are 350-6593, 510-534-51 or 599-85-2441


[Modified by burners, 1:31 PM 3/25/2002]

 

And when you get it installed, you will wonder how and why you ever did with out it. :yesnod:

 

Interesting. So, all these solutions are permanent (eg. I have to weld them into the pipe), correct?

Is there a "temporary" way to do this? Is there something that could be attached to the back of the exhaust pipe where this would still work? Could I make a "plate" that fits inside the pipe with this attached? Finally, is there any reason this just can't sit in the back of the tail pipe and still work? Does it need to be really close to the combustion chamber?

Thanks!

 

Yes, it should be as close to the exhaust port as possible. If practical, you would want one per primary tube on a set of headers so that you could check the mixture in each cylinder. The way it works:

The O2 (oxygen) sensor is a device with a material in it that becomes a battery with the introduction of oxygen to it. Also, it can generate electricity from enough heat. Basically it is a small catalytic converter that instead of cleaning your emissions, measures them based on the amount of heat and/or oxygen in your exhaust.

Placement is very important, and they should be as close to the collector as possible. A "bung" (threaded piece of steel) needs to be welded onto a pipe that has a hole cut in it for the sensor to stick through. The nice thing? The sensor and a standard sparkplug for a 1969 Corvette have the same threading, so for a non permanent solution, you can put an old spark plug in the hole instead of always running the O2 sensor.

On reading the sensor, I'll dig up the chart, but it varies from 0-1V output based on the amount of oxygen in the exhaust. Voltages compare to A/F mixtures...with say .875V equating to 13.5:1 A/F ratio. .875V thus equals 13.5 parts Air to 1 part Fuel. :smash:


[Modified by rainman69, 5:47 PM 3/25/2002]

 

METER READING FULL THROTTLE AIR/FUEL RATIO
.000 17.0:1
.100 17.0:1
.200 16.0:1
.300 15.5:1
.400 15.0:1
.500 14.7:1
.600 14.6:1
.700 14.5:1
.800 14.2:1
.875 13.5:1
.900 13.2:1
1.000 12.5:1



[Modified by rainman69, 5:47 PM 3/25/2002]

 

Would this be something that I would want to drill and tap directly into my exhaust manifold? Or, should it just go on the exhaust tube right below the manifold?

I assume once this is connected I use it to adjust my mixture screws on the carb?

Do all the sensors read the same? So I can just get a sensor, have it welded on, and use my voltmeter to test?


[Modified by Corellian Corvette, 8:15 PM 3/25/2002]

 

That's pretty much it. You can make sure you are running the correct metering rod for you Q-jet. You will be able to get it close to perfect at idle I would think.

 

rainman69 - What part # / brand of O2 sensor were you using here? I just tested mine and the curve is a LOT flatter. I would like to try yours, the resolution seems much better.

rocky

 

One thing to note is that not all O2 sensors are the same. The cheaper sensors are narrow-band sensors.. these sensors are meant for a 14.7:1 ideal air/fuel ratio, and aren't very accurate away from this point. The more expensive (but more accurate) alternative is something called a wide-band O2 sensor. The sensor itself might cost $170 or so, but it's more accurate and the range of ratios is much bigger. A sensor like this will allow you to tune your wide open throttle mixture, whereas a narrow-band won't.
For any electronics tinkerer types, there's info available for a do-it-yourself wideband O2 meter at http://www.diy-wb.org
Not to say a narrow-band O2 sensor isn't any good... for the money it's a great and useful tool!
As far as installing the sensor, you can buy the bung from somewhere like summit, then have it welded on at your local muffler shop.
-Jason

 

This link provides a little better explaination of why a narrow band sensor is not really suitable for tuning. Yes they can look like they are providing usefull information but if you are running a high HP setup you need to step up to the wideband sensors.
http://www.brownsword.ca/afmeters.html

Tyler

 

Go here - this is a good article to read up on this - I installed the Nordskog guage and like someone said above it really tells you what is going on! I took the pipe to midas and they welded in the adapter and also had a plug that they gave me so I can remove the sensor in the future if needed.
http://www.chevyhiperformance.com/in...rticleid=53159


[Modified by kostutsman, 10:18 PM 3/25/2002]


[Modified by kostutsman, 10:20 PM 3/25/2002]

 

That should be pretty much any heated O2 sensor from my understanding. But, I've been wrong before.

 

This implies it is as good as a wideband sensor.

"Unfortunately, it’s not a safe bet to rely on this
air/fuel gauge for accurate WOT air/fuel ratio
While the early versions of this air/fuel meter
were promising, a better way to go would be
with a meter that indicates a full range of air/fuel
ratio from 12:1 to 17:1. That’s exactly what the
Nordskog air/fuel mixture gauge does. The
system is designed to use a standard heated
oxygen sensor, which is located in the exhaust
pipe at or near the header collector on one side
of the exhaust system. This voltage signal is
converted into a readout that is displayed either
digitally or with a 270-degree analog-style
gauge."

This tells the truth.

" The voltage signal at 12.5:1 to 13.0:1 is
not nearly as accurate as it can be around
14.7:1 where the sensor is designed to
operate. Therefore, the error factor is likely to be
fairly high at best power ratios. For WOT jetting,
it’s best to do that at the dragstrip where you
can use trap speed to tune the car for best mph
readings. "

Talk about deceptive!

Tyler

 

kostutsman - which guage did you use with the sending unit?

This has me almost more confused now than before. Do all the guages have the same readouts? I see that I should be able to use just the sending unit and a digital meter to do the adjustments.

I'm not looking for super-performance accuracy. I would just like to tune the car somewhat accurately at idle instead of using the old vaccum/tach guage to adjust the mixture, so I don't want to spend a ton of money if I don't have to.

Thanks!