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914World.com _ 914World Garage _ Anyone have experience with Air/Fuel Guages?

Posted by: dcruiksh914 Oct 4 2005, 09:41 PM

After it was suggested that installing an O2 sensor and Air fuel gauge would make tuning a much easier and more accurate task, I got the stuff and went for it. I got 2 O2 sensors and 2 gauges (one for each exhaust bank), and installed. I used the 3 wire sensor as I had read that the 1 wire needs the heat of the engine to get it going. So, everything is in, and it doesn't seem to be working, or I've got a strange problem. The gauges, which have a five bar LED readout ranging from Lean to Rich, suggest that I'm running very lean (just one bar lit). Sometimes, that bar goes out and I get no readout at all. I can adjust my A/F mixture screws all the way out with no affect at all on the gauge reading. I know my car has been running rich, so if anything, the gauges should be indicating the extreme opposite. I called the Summit tech line, and they said that I have everything installed correctly and it should work.

I'm running a 3.0SC engine with webers and 916-6 factory heat exchangers. I placed the O2 sensors about 2" down from where all three pipes come together.

This seemed like a great idea, but now...

Anyone have any experience with doing this and any thoughts about what's going on here?

Posted by: McMark Oct 4 2005, 10:10 PM

You can search for wideband o2 sensor and read a ton. Short version, narrow band (1,2,3, or 4 wire) is garbage for tuning. Wideband (5 wire) is what you need.

Posted by: iamchappy Oct 4 2005, 10:13 PM

First off the engine really needs to get warmed up before they ar gauge will start to read correctly. I personally didn't like the scale read out or the led number read out although the number read outs are suppose to be the most accurate . I prefer the analog type which is easier for me to read at a quick glance.
Westtach is the gauge I am using.
http://www.westach.com/images/showcase/2C5-56-Air_Fuel_Ratio.jpg
http://www.frostalarm.com/cat/p2.html

Posted by: lapuwali Oct 4 2005, 10:14 PM

Sorry to say, but what you bought is only marginally useful. The three-wire O2 sensors are so-called "narrowband" sensors. These will do a fine job, in some cases, of telling you when your mixture is exactly 14.7:1, or lean, or rich. However, they don't tell you much about HOW lean or HOW rich. The extra LEDs are basically window dressing.

The other problem with narrowband sensors are that they're very temperature sensitive, and will generally work very poorly, if at all, if they're all that far from the exhaust ports. These sensors must be hot to work at all, and temperature variations can throw off the readings considerably. The two extra wires (one is the sensor wire itself) are part of a heater circuit that's supposed to alleviate this problem somewhat, but it's completely unregulated and is mostly there to allow the sensor to heat up faster after a cold start.

Compounding all of this sounds like you're having signal quality problems. The ground path for the signal is supposed to be through the exhaust pipe, and some exhausts don't provide a very good ground. You could try to get a four-wire sensor, which includes a dedicated ground wire, and run that to a good ground point.

However, you'll get far more accurate results if you just ditch what you have here and buy a wideband setup. There are several places that sell these now, including Innovate Motorsports, SDS, and AEM. These will give you an accurate AFR reading from 10:1 to 20:1, they have a well-regulated heater circuit so sensor position isn't as important as with a narrowband, and you'll be able to actually tune you engine to an AFR suited to making good power (roughly 12.5 to 13.5:1), rather than an ecomony/emissions compromise, which is the best you'd do with a narrowband sensor.

Posted by: Jake Raby Oct 4 2005, 10:27 PM

Buy the LM-1 it works excellent.. I use it in the R&D car and in my 912E

I also like the unit I use on my dyno available from www.sdsefi.com

If its not a wide band O2 don't even bother buying it..

Posted by: EMRoadster Oct 6 2005, 08:52 PM

Excellent tool, the only way to go if you want mixtures to actually be correct.

http://www.innovatemotorsports.com/

Posted by: iamchappy Oct 6 2005, 09:00 PM

My gauge just gives me an estimate on whats going on, certainly not something to tune by. I am very sure the LM 1 will find a way into my tool chest.

Posted by: Mark Henry Oct 8 2005, 04:06 PM

QUOTE (EMRoadster @ Oct 6 2005, 10:52 PM)
Excellent tool, the only way to go if you want mixtures to actually be correct.

http://www.innovatemotorsports.com/

Same one that SDS sells.

Posted by: Brett W Oct 8 2005, 09:42 PM

Get the AEM gauge. It works well and can handle datalogging. Its also easy to read.