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Join Date: Sep 1999
Location: Santa Rosa, CA
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exhaust gas analyzer

I'm interested in finding out about gas analyzers for tuning FI or carbs. I guess that a CO meter is sufficient for much of this kind of work. I'm not interested in testing to satisfy clean air requirements, I just want to check mixture; essentially what is done by checking spark plugs. Does anyone know of an inexpensive CO meter, perhaps a DIY type? Are there other things to monitor that are as revealing as CO or are cheaper to test for?
Old 10-07-1999, 10:20 AM
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I looked into this same question a while back and found the cheapest one I could find was still around $1200 or so! So I made an air/fuel meter for our Turbo and it works pretty well tapped into the O2 sensor line. That is about $200 or so for the whole setup to put one on a 914 as you would need to add the O2 sensor on the exhaust, etc. There are some of the people here that have done just that.
Old 10-07-1999, 11:03 AM
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I had emailed Mark Stephens asking them what they used to provide their customers.
They use a unit at CBPerformance, its about 100 bucks. I think it goes directly into your tail pipe, Stephens advised you drive the car on level ground to tune the A/F ratio. If you purchase it post an update here, I'd like to know how it well/awfull it works.
Old 10-07-1999, 12:27 PM
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I think the CB unit is an Air/Fuel gauge and has an adapter that can bolt in the line between the collector just before the muffler and you can remove it after you are done tuning. The adapter is a pretty neat idea and makes it really easy to put a gauge on a car without welding a boss on the headers.
Old 10-07-1999, 01:17 PM
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There are a couple of exhaust gas testers listed in the JC Whitney catalog and they sell for between $150 and $250.

Alpine
Old 10-07-1999, 02:58 PM
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I checked the JC Whitney online catalog and they've got a CO meter for $130. Thanks for the responses.
Old 10-07-1999, 04:11 PM
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There are a few gauges made for about $30-40 by Cyberdyne and others. These can be had from Jegs or Summit (muscle car catalog houses). Check their web pages. They are glad to send a catalog. You need to add an O2 sensor to this since our 914 lack such. Get a 3 or 4 wire O2 sensor, not a 2-wire, unless you plan to mount it very close to the cylinders. The 3 or 4 wire sensor uses the extra wires to provide power to an internal heater element in the sensor. O2 sensors do not read at all until hot and not correctly until about 600 deg F. The 3-wire O2 sensor used on many Fords should work and is relatively cheap (~$35 at Autozone). According to a book I read on Ford fuel injection systems, the black wire is the sensor output and the two white wires are for the heater (12V), but you might want to double check that. (I wrote to Bosch, in german, but never got a reply).

There are many sites on the web showing DIY LED gauges, but at the end of the day, the store bought may be about the same price. Here is one example: http://www.ncf.carleton.ca/~bm959/afr.htm
They all seem to use the same LM 3914 chip to drive the LEDs. The only reason I can see to make one yourself is to have a horizontal line of LEDs in a retangular box instead of a big round gauge.

One last note: I have read some comments that just sticking the O2 sensor up the tailpipe will not work. The dialog goes like this... The O2 sensor does a comparison between ambient air and the O2 in the exhaust. (ideal ratio at idle is 14.7:1) As such, the tail (wire side) of the sensor must be in the ambient air. Sticking it up the tailpipe would put it all in the exhaust stream. Can anyone authoritatively confirm this information? Seems to make sense to me since we are talking about a ratio and the only way to get a ratio is to compare to ambient air as the % O2 in the air changes with altitude, as we in Colorado know all too well. (Add 5% to the AREA of your main and idle jets for starters at 5000 ft abouve sea level).

I have a Bursch exhaust system and am considering mounting the O2 sensor in the CAT bypass pipe. If it does not work out, atleast I only have to replace a ~$20 pipe.

As you can see, I have been researching this for a few months, but have not yet committed myself to one approach.
Old 10-08-1999, 05:54 AM
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I would opt for the air/fuel setup since it will be on the car all the time. I made the LED unit similar to the one referenced above and I used real large red LEDs on the lean side and regular sized yellow and green for normal and rich. I was worried more about the mixture going lean at full throttle than I was about exactly how close it was at idle. It ends up being right about in the middle of the lights (10) at idle so it is pretty accurate. I did have it checked against a very accurate SUN test station to make sure it was close to reading the true value.
Old 10-08-1999, 06:16 AM
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Here's an even better web page on the topic: http://www.students.tut.fi/~eppu/dev/EGO-bar.html
Old 10-08-1999, 06:29 AM
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I've got this on my cars;

$17 single wire O2 sensor from local auto-parts store. Dosen't matter what type, all O2 sensors read the same. The multi-wire O2 sensors are simply shielded grounds and heater wiring.

$50 Auto-Meter A/F gague, from local performance shop. The Intellitronix gagues from JC Whitney are just as good however not as good looking IMHO.

Hook 12v, ground and wire from O2 sensor to A/F gague. Volia continuous A/F readings all for < $100.

I'm running this on the 914 for setting the little knob on the ECU. Actually my Girlfriend puts ~80% of the miles on the car and she just notices that when the LEDs are not reading yellow (for this gague perfect mix) she pops the lid and adjusts the knob. It's so easy a 20yo girl that can't change the batteries in a smoke detector can tune it! Better yet it's so "pretty to watch" she tells me if and when the tuning changes!

Well worth the time and effort. Then again so are the left and right head temp sensors I installed!

Ian
Old 10-08-1999, 06:35 AM
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FYI

I onced worked at the Bosch plant that made the O2 sensor. Basically, there are four possible wiring combinations seen below:

1. 1 wire. This sensor does not have a heater element. A good sensor for engines that run hot.

2. 2 wire. Same as the 1 wire, but a ground wire attached to the case of the sensor.

3. 3 wire sensor. The black wire is the signal wire, the two white wires are the 12V heater element. Polarity on the heater wires is not important.

4. 4 wire sensors. The ground for the black signal wire is isolated from the metal of the sensor. The 4th wire is used to provide the ground path.

IMHO, the 3 wire sensor is best for installing in a 914 exhaust system.

I hope that this helps.



------------------
Smoke Daddy
Old 10-10-1999, 03:52 AM
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