omniphil

Ok, so on the dyno at WOT with a wideband sensor stuffed up the tailpipe i'm running between 11:1 and 10:1 - RICH! But the rich/lean gauge in the car shows between .80 and .85 volt to the O2 sensor? that sounds a little on the lean side to me? I usually like to see about .90 when I tune my other cars. Is my gauge wrong? I have it hooked directly to the battery for the ground and directly to pin 24 on the DME, all connections are soldered just to make sure. Car is an 86' 951.

rage2

those lean rich gauges aren't accurate. On track days, after a lap, the O2 sensor gets hot, and the gauge is way off. Shows too lean even though I'm running 12:1 A/F as shown on my wideband logger.

Dave Sims

<a href="http://members.rennlist.com/martintaylor/new.htm" target="_blank">http://members.rennlist.com/martintaylor/new.htm</a>

Any comments ??

shaheed

nice but it still doesn't address the issue of the stock O2 sensor not being accurate

Dave Sims

Take two:

<a href="http://www.lambdaboy.com/main.html#PRODUCT" target="_blank">http://www.lambdaboy.com/main.html#PRODUCT</a>

Danno

"nice but it still doesn't address the issue of the stock O2 sensor not being accurate"

Welll... the problem really isn't that the narrow-band O2-sensors are inaccurate, it's the electronics that create the display that's not very good. Using analog meters and voltage-comparators to drive an LED bar is the problem. Part of the issue is that they're trying to display the full 10:1 to 16:1 range on a linear bar-graph when the signal itself is non-linear. If you narrow down the area of interest, namely from 11.0:1 to 13.0:1 for full-load operation, you'll have a simpler signal to deal with:



Note that the voltage-range from 0.800 to 1.000v is fairly straight here. Spreading this narrow range out across 10 LEDs will yield much more accurate results. But that's only analog electronics.

Martin's design uses a PIC microcontroller with 0.001v accuracy. This voltage vs. air-fuel ratio is programmed into a look-up table. Then digital electronics compare the measured voltage to the values in the table and lights up the correct LED. This method allows shifting the display based upon the temperature of the sensor as well (using one of the other temp-sensors as a proxy for exhaust-temperature). It also allows the gauge to be custom-calibrated to any O2-sensor out there. Even WIDEBAND O2-SENSORS !!!

Dave E

Martin's product seems great, Danno, any experience with this? It should work with the 944's stock sensor, as that was the original design mule, right? <img src="confused.gif" border="0">

toddk911

Or buy GURU chips and you know you have the perfect a/f

I think I will dump my a/f guage on ebay and pick up a Link Knock sensor. I know my air fuel is right now, so I don't need to monitor the a/f as much as I need to know if there is actually knock. With the Link Knock sensor, just crank up the boost until you see Knock light, then dial it back a bit. Not sure about the 180$ price thoguh

christian

I emailed Martin but did not get any answer. Any ideas?