CO METER SURVEY

[wwheeler]

I wanted to get opinions about the exhaust CO meter.

I am considering buying one to fine tune my Air/fuel mixture. Do people find them absolutely necessary to get the right tune or are most people satisfied by using the famous "Blacklick CO Meter" and then fine tuning for best idle? Do many people have their own or just use a shop's?

What is a good brand and how much would you expect to pay for it? Is it straight forward to use or do I need a degree to figure it out?

Thank you for the input!

[Cees Klumper]

Hello Wallace - I got a used CO meter by Gunson (Gunson Gas Tester Professional) - I don't recall what I paid exactly, but probably it was around EUR 150. I calibrated it against a proper garage CO meter and it proved quite accurate. I like knowing from a true CO meter where the car is, although it only measures CO at idle. As you probably know, the FI pump has different settings for idle, partial and full load. I believe the BBB calls for CO readings while driving, and shows photographs of a CO meter sitting in the passenger seat while the car is on the move. So although I know and can influence the idle CO, I can only hope that the FI pump is able to maintain the proper settings at operating speeds.

If you search on Ebay or Google for this Gunson apparatus, you should be able to find both new and used units.

[abe280SL]

Another for GUNSON..
abe

[erickmarciano]

do you find with the Gunson when you leave it in the tailpipe for more than 2-3 min the reading does way to high.
thanks

[ctaylor738]

I have had a Gunson for about 5 years, and it seems to work well for the CO ranges for our cars.  On newer cars, it gets flakey under 1% and will sometimes go negative.

It does seem to drift higher the longer it's in the pipe, but it returns to close to the calibration value of 2% if you set it in clear air for ten minutes or so.   The directions do say to take the reading quickly after sticking the probe in the pipe.

[JimVillers]

I have a wide band A/F monitor from PLX.  I bought it off of eBay as being the cheapest available a couple of years ago.  If doing it again, I would have bought a Innovate gauge. http://www.innovatemotorsports.com/.  I highly recommend a Wide Band monitor.

I made mine portable by attaching the sensor to the tail pipe with an aluminum tube.  I plug the system into the cigarette lighter and am able to monitor the Air/Fuel ratio as I drive.  While I have not used it on my 230SL as it runs very well, I have used it to select Weber jets for my 190SL and my MGB>

[awolff280sl]

Hi Jim, how do you use an air/fuel ratio monitor to tune our cars when the original specs utilized CO%?

[JimVillers]

Andy .... I aim for 14:1 fuel/air as a reasonable number.  I have not tried it on my 230SL yet but on my 190SL, I would drive a low speed, very little throttle (idle jet), speed up slowly to watch the transition between the idle jet and the main jet and then cruising and full throttle.  My target range was between 15:1 and 13:1 during each phase.  When I started, the car had a flat spot between 2500-3000 and the meter indicated that it was very rich.  Installing a smaller idle jet corrected the flat spot but put a hesitancy between 2000-2500 that was lean.  I then changed the "F" number of the idle jet and the car ran MUCH better.  I went through a similar process with the main jet, air correction jet and emulsion tube.  It took a while but would not have been possible without a wide band air fuel meter.

[waqas]

So I take it they use any old oxygen sensor for the air/fuel measurement? Presumably, the O2 sensor has to heat up before accurate readings can be taken.

For a while now, I've been thinking about rigging my own setup using an O2 sensor installed in the down-pipes (wires routed through firewall into cabin, under dash). This way, whenever I need to make adjustments, I can simply hook-up a voltmeter and take measurements under load. Of course, an AVO meter with an old-school dial gauge readout would be much better for low-pass filtering the jumpy readings, which is what the commercial box likely does.

It's good to know that this approach can indeed yield useful results.

[JimVillers]

Wagas .... There are narrow-band and wide-band A/F sensors and gauges.  The narrow band is "any old sensor" and it basically says rich or lean.  The wide-band gauge will provide a 2 digit accurate read out between about 11:1 and 18:1.  Cost; narrow-band $50; wide-band $300.