From the MMA message board...
I am going to tell you how to build a rich/lean gauge for your Mopar.
It is not hard. You need only an oxygen sensor to fit into the exhaust pipe and something to read voltage. This can be an actual volt meter or a LED device.
You can buy these as a ready made kit if you like. I have found it a great help in getting my sixpack to work and I really, really think Pete would benefit a LOT from one of these.
I will even give you an electronic diagram to show you how to build your own LED indicator if you are the electronics whiz kid type. I gave Jay Gilmore a copy of this a while ago and it has been 'under development' for a while but because Pete is having so much grief I think it is only fair to let everybody in on how easy this is.
The oxygen sensor you need is a part of every day life in modern cars. You can even find them on cars in scrap yards now. They come with either 1,2,3 or 4 wires coming out of them. You only need the sensor wire which is normally black. The other wires are for a pre-heater which you don't need and sometimes one is an earth lead.
The sensor has a threaded end so all you have to do is cut a hole in one exhaust pipe as close to the collector as possible and weld a nut over the hole so that the sensor will screw in and protrude into the pipe. You then need to connect it up to a 12 volt source switched from the ignition switch and wire in a volt meter to join the hot wire and earth (not in series with it).
A digital meter might not be the best thing to use in this case as the display can change very rapidly. A normal 12v gauge is all you need although it will help if it has a good scale.
All you need to know now is what the different voltages you will read actually mean.
Well I left that information at home so you will have to wait!
Get cracking Pete.
By Martin Edridge (Martin) on Friday, July 20, 2001 - 04:35 pm:
Spot on, Dave. Did this a few years ago just using a DVM. IIRC, about .890-.920 was a good value to shoot for if looking for max power. Prone to being very innaccurate at less than full tilt due to lack of heat in the pipes. Guess I should have used a heated 02 sensor. I did ask you a while ago about doing an LED box for this job but you didn't reply.
By Gavin Chisholm (Mrnorm) on Friday, July 20, 2001 - 05:35 pm:
You can use the heated O2 sensor, which improves things a bit (for example if you want to see what your engine is doing when it's cold), but the regular is fine. If you use one with leaded gas though it will not work for very long.
I have a couple of sensors that will find their way into my new exhaust, it's a really good idea. I have some excellent web links which are pretty comprehensive, I will try to post them later.
Some people sell the aftermarket LED meters, and claim that they are 'air/fuel' meters, showing a lamda range from, say 9:1 to 16:1 - don't believe them!! Unless you go to a very expensive UEGO sensor, a normal O2 sensor (an EGO or HEGO) will really only tell you if you are either rich or lean. Still very useful, but more LED's don't make it more accurate. EGO sensors are very non-linear, they transition ('switch') from rich to lean very quickly, meaning that you can't really tell how rich or lean you are with any accuaracy, just that you are either rich or lean - your title is dead right Dave (no surprise).
Anyway, top idea, everyone should use them!
(Yes Sandy, I know you already have one! Maybe even 4?)
By David Robson (Dave) on Friday, July 20, 2001 - 08:34 pm:
Sorry Martin. Jay swore me to secrecy! I will print all the details I have sometime over the weekend.
By David Robson (Dave) on Friday, July 20, 2001 - 08:39 pm:
Just to keep you going...
Under 250mv = Too lean
250-410mv = Good cruise mix for mileage
410-580mv = 14.7:1
580-800mv = Rich but good WOT power
Over 800mv = Too rich
By Gavin Chisholm (Mrnorm) on Friday, July 20, 2001 - 10:42 pm:
There you go boys, this is not a bad article at all, and has a good bit on EGO sensors.....
http://www.bob2000.com/carb.htm By Sandy Mercer (Sandy) on Saturday, July 21, 2001 - 01:48 am:
Dragged kicking and screaming into the late 20th Century, eh ??
Gavin,
GN has one O2 sensor (pre-OBDII by years) up by output of turbo. It is a one wire sensor, earths through the downpipe.
On the laptop, 750-800mV is what you aim for. Best power comes at just the lean side of rich (if you see what I mean). 470mV is stoich.
Between 800 and 850mV is okay but rich. I tend to launch rich (hence crappy 60 foots), say 850mV then the car leans out through the run. My car has always done this for some reason, but I have a little boost creep, hitting 22psi or so at the end of the track and O2 has dropped to about 750mV. Not too concerned, except when I get detonation.
In the States where the turbo Buicks guys get 116 octane race gas that is leaded they go to heated sensors, or just throw them away after a race day.
They do foul up very badly with lead, and basically go off.
There is no feedback to the management system at full throttle. The system goes into Phase Enrichment, and the injectors go to about 110% duty cycle (hmm, tell me how injectors can be open 110% of the time
) But the car basically run a fixed set of values at full throttle, and the O2 is 'tuned' by upping fuel pressure to richen or upping boost to lean ...
If you guys are tuning for power though, forget O2 and buy a digital EGT (exhaust gas temperature) gauge and aim for 1550F or so.
By MoparKev (Kev) on Saturday, July 21, 2001 - 04:10 pm:
HOORAH! I've been waiting for Jay to pull his finger out for about a year now! Very interested in the circuit diagram Dave. Where do these sensors live on modern scrapyard type motors? Do most injected cars have 'em? What's the difference 'tween O2 sensors and Llambda sensors?
By Gavin Chisholm (Mrnorm) on Saturday, July 21, 2001 - 06:58 pm:
Kev just use a DVM, no circuit required. The sensors are located before the catalyst in the exhaust pipe, if you look at the link I posted it has a good pic of what one looks like.
An O2, or EGO/HEGO just senses the presence of oxygen in the exhaust - excess oxygen = running lean. Of course once you are using all the oxygen (stoichimetric) it can't tell how rich you are, but it kind of acts as a temp sensor in this range. As I said, it won't give you a real air/fuel ratio, at least not with much accuracy, but it will tell you whether it is rich or lean, and just around stoich its good enough to do the job.
A Lamda sensor will actually measure the air/fuel ratio itself - 10:1, 12:1 14:1, etc. Better than an O2 but a lot more expensive. A UEGO does this, and from the name I have to assume that it also works by sensing oxygen.
By David Robson (Dave) on Sunday, July 22, 2001 - 09:59 pm:
Right. Lets get back to this.
Because I did not have the figures on my when I started writing this I did not realise the voltage scales we would be working on. So I think the cheapest (and easy) way of doing this is with a cheap digital meter.
And that is what Mr Ehrenberg suggests!
But I took the easy path and bought a complete kit. much easier to read.
There are several different makes but all work the same. Hooker headers even make collector reducers with a threaded mounting boss for the sensor!
First you need to aim for stoichiowhatsit all round. Then once you have that settled down you will want to increase the part and full throttle mixture to 12:1 for best power.
Out of interest. That equates to a fuel flow increase of 20%. No wonder we don't get many to the gallon!
Looking at it the other way. Best economy (without getting too lean) is 15.75:1. That equates to a decrease in fuel flow of only 7%.