john banks

It is reproducible on one vehicle to <20mV under similar conditions as I can demonstrate with multiple datalogs of the narrowband on my car. Most Link remapping in the UK seems to be done using narrowband sensors, and Bob I believe achieved similar results comparing narrow with wideband. Granted they read over lean when the EGT goes high and there is a lot of non-linearity but it is certainly useful to have 20mV resolution - I have adjusted fuelling and had reproducible results with it although a wideband would of course be desirable. If you read it for a short period after a cruise it works very well indeed.

If as you claim it is not accurate to 100mV, then it is totally useless even for telling if you are remotely rich or lean. At 800mV at full boost you would very probably have a serious detonation problem, whereas 900mV is very rich indeed. If you have an LED for 900mV and it is not lit is it 880mV and still safely rich or is it 800mV and your engine is about to pop? The LM3914N chip in most AFRs triggers at 0.1V intervals in a typical 10 bar setup and that configuration is entirely useless.

[Edited by john banks - 5/2/2002 7:32:48 PM]

MattH

Some one on there was selling kits to make your own AFR Meter!

Any leads?

Sparks

Have a look at

http://www.scoobynet.co.uk/bbs/threa...ThreadID=57428

ustolemyname??stevieturbo

iTrader: (1)

Check out www.autospeeed.com or www.jaycar.com.au
They both sell kits ( both jaycar kits anyway ). Fair enough they are in australia, but with a little credit card anything is possible and they are quite cheap anyway. I have bought stuff from them both and it has got here faster than some stuff I have bought locally!

MattH

ustolemyname do you have any pics as it sound good and it costs about 23 pounds, autospeed don't work and the pic is missing on Jaycar

If you don't have any pics what does it look like size quality etc

Matt

john banks

You can find pictures on the Autospeed site of this - try search in Google with Autospeed Jaycar AFR

Trouble is from the circuit it looks like they are starting the reading at 0V rather than a more interesting 0.7 V or more. Anything below 0.7 V is just a disco effect and is not showing you much useful information - you need to be reading to the nearest 20mV to make any sense of the info at all, hence why I modified a similar circuit to the Jaycar and others to do this in the thread above. Depends on what you want it for, but 0.8 V and 0.9 V is the difference between very lean and very rich on boost - for reading on full boost you want the range say 830 to 930mV - most cars run over 900 mV. You could say that you are looking for the 0.9V light to show, but it is a bit imprecise.

You could also use a digital voltmeter if you want. There are digital displays about, some even show you the value as an AFR.

ustolemyname??stevieturbo

iTrader: (1)

A std narrow band lambda output can vary a lot depending on temperature variations. To say that it would be accurate to 100 mV just is incorrect. These AFR kits are only a rich/lean guide as the instructuions will clearly state, not an accurate tuning device.
On the other hand, for a few ££ more check out....
http://www.techedge.com.au/vehicle/wbo2/default.htm

It is a lot more expensive than a simple AFR kit ( not much more than a Link AFR tho. I have one, and although it is a little tricky to build ( I bought 2 kits initially, and as expected blew the first one up as my electrical knowledge is rather limited, so my advise is that it may be better to buy it built )
When I bought the 2 kits a couple of months ago they cost me £120 all in + a UEGO sensor at £130 ( damn customs+excise )
Assuming it is what it claims, it is an accurate AFR meter. And it does seem to work well once calibrated.

MattH

Cheers guys I've now ordered one, 10 led array and a three digt LCD came to $80 inc shipping, about 30 quid, VAT and duty souldn't be much mare that a tenner so mony well spent. That the opinion at the moment, will let you know when it fitted

ustolemyname??stevieturbo

iTrader: (1)

Narrowband sensors are only accurate at stioch. 14.7:1 approx 0.5v
I quote an article on oxygen sensors.. from autospeed ( sorry copyright! )
"Specifically, one sensor cited in the literature had an output of 860mV at 900 degrees C, which corresponds to an air/fuel ratio of 11:1 air/fuel ratio (which is very rich). At a sensor temperature of 650 degrees C, this same output voltage would indicate an air/fuel ratio of 14:1 (much leaner). This means that, at high temperatures, oxygen sensors typical read leaner than the actual air/fuel ratio"
Having said that, I too have used the narrow band to seemingly good effect in the past, but I am now using the wideband kit as I have the means to adjust !! motec...

MattH

I don't know to much about this stuff but I'm working on the fact that when running standard boost the fueling is correct, so where ever it reads, it can be the marker as the point it need to be, as I increase boost then I should be able to ajust the fueling to get the same characteristics as before.

Also the AFR I've ordered is adjustable and has a 3 digit LCD which I asume reads mV's, so should be able to set it to read correctly.

Am I righ in thinking 800mV is where it needs to be at full tilt, just before deting as I realise there is a fine line between the two.

john banks

It will be more like 900mV to be safe - Link manual recommends 870 mV, most standard Scoobies run 910-930 mV - it will drop as it heats up but it is decent for a drag run in 2-3 gears at least, which if you are logging can give you quite a lot of info.

mrkimpreza

Just fitted my home built AFR. LCD panel / voltmeter modified for the range of 0-2V. Fed by 9V battery. Three digit behind decimal point and accuracy of +/- .5%.

Splice wire B136, pin21, and fed it to the voltmeter. Works fine, HOWEVER:

- First time I took ground from the ground wire running to my oil temp gauge. When I put on the light the voltages on the AFR drop 0,1V (so it's useless)
- Second time I took ground from one of the bolts which holds the ECU. It's better, it now drops 0.01 V when the light is turned.

What's the best option ? Splicing GND from ECU or running the ground wire all up to the 12V in car battery ?


Mark.

john banks

Apparently the battery ground is best.