Lambda input

morts · Post by **morts** » Sun Feb 15, 2009 12:55 pm

Hi!

I'll soon be receiving my megajolt and i'm very excited.

I'm very interested in the aux input. I've looked around here and found a few articles on knock sensing, wideband logging and about the mod to allow 0-5v input.

At the moment i've been using a lambda sensor and a voltmeter to try and sort out fuelling on my carbs and it has been working quite well. Its crude with 0.5 volts being stoichiometric and 0.2 volts being rich and 0.8 volts lean but as carbs aren't fuel injection it has worked quite well.

What i would like to know is. Is it possible to just wire the lambda sensor directly to the aux input and log the voltage changes along with the engine speed and load etc? I don't want the voltage converted to anything just logged. If so how would i wire it up? I'm using a universal 4-wire sensor.

I like the innovate devices but just don't have the money and if the above worked it would be enough for my requirements.

DannyP · Post by **DannyP** » Sun Feb 15, 2009 1:16 pm

Yes. I don't know about v4, but you need to protect the processor with a buffering circuit on v3. Direct voltage datalogging of the aux input is very easy to implement and should get you on the right track. Have fun.

You'll have to get the manufacturer's specs on your O2 sensor. Is it a wideband unit? If voltage is from 0-1 it is a narrowband unit, isn't it? I've never seen a 4-wire narrowband though, they tend to be three. 2 white wires for the heater and a black one for lambda. Ground or earth is through the threaded portion. Perhaps that is the fourth wire on yours, a ground? A simple volt-ohmmeter should tell you that.

morts · Post by **morts** » Sun Feb 15, 2009 2:58 pm

I guess i must be using a narrow band then. I don't really know much about lambda sensors all i know is it was cheap. I'm sure it had four wires i'll check i may just be going loopy reading all this info and thinking i do.

Any idea on the voltage reading for a proper wideband sensor?

DannyP · Post by **DannyP** » Mon Feb 16, 2009 2:40 pm

Zero to 5v. There is a cheaper route than Innovate, the JAW, at 14point7.com, but I have no personal experience. Website looks like it is a similar project to Megajolt, and about $70-80 for the unit plus $50(All USD) makes it less than half the price of a commercial controller. You could even leave off the display and just datalog the voltage via the AUX input. If you calibrate the input, you could directly display the AFR on the Megajolt controller, nice!

morts · Post by **morts** » Mon Feb 16, 2009 4:44 pm

I meant voltage on the wideband in referance to lean and rich etc as in the 0.2v on the one i have is rich.

Thanks for the link but i really don't have any more money to spend. I will look into it for the future though.

Do you know how i would wire a lambda directly to the aux input and how i get the program to recognise and record voltage?

DannyP · Post by **DannyP** » Tue Feb 17, 2009 4:08 am

The JAW site says you can configure output voltage to equal a/f ratio divided by 10, i.e.; 14.7:1 shows up as 1.47 volts.

In the how-to it shows how to configure aux input, doesn't it?

http://www.autosportlabs.net/MJLJ_V4_ve ... put_source

morts · Post by **morts** » Tue Feb 17, 2009 10:40 am

It probably does but i'm new to this forum and it'll take me a little while to get round it all.

morts · Post by **morts** » Tue Feb 17, 2009 10:56 am

Right so having read all the bits all i need to do is make the board mod, wire the output of my lambda directly to the MJLJ's aux input and the ground of the lambda to the ground on the MJLJ (it is a 4 wire 1 volt sensor that i have) and then setup some kind of scale for the incoming voltage and then dataog it and i should be able to see the values against the rest of the engine info.

The MJLJ doesn't care what the signal is coming from it just records the output voltage so If i decide to use a 0-5v sensor then i just have to rework the scale.

I can pretty much use any lambda sensor then.

Correct me if i'm wrong

DannyP · Post by **DannyP** » Wed Feb 18, 2009 2:38 am

Wideband sensors MUST use some type of controller to get any output from them plus control the heater elements inside. Narrowband, not the same problems at all.

morts · Post by **morts** » Wed Feb 18, 2009 10:30 am

Sorted

Just out of interest should i have a controller for the heater on the narrowband sensor? I haven't been using one

I assumed it was just a set resistance to a 12v supply and controlled itself!? oops.

If i do then sod it i'll go and get a 2 wire sensor and just wait for it to get up to temperature. I only want the sensor for tuning and then it will be disconnected until i change something engine wise again.

Thanks!!

DannyP · Post by **DannyP** » Thu Feb 19, 2009 4:09 am

No controller needed for narrowband sensor, just 12v and ground across the resistance load.

morts · Post by **morts** » Mon Feb 23, 2009 12:53 pm

Well after all this i'll be going with a wideband sensor and controller.

I discovered that the 0-1v sensors only really cover about 0.5-1:1 of the A/F ratio each way around 14.7:1 so for a carb setup this is useless as we would probably be happy enough with that much of an error around 14.7:1 and not knowing how rich or lean we are by that small a reading means real guesswork on any adjustments. It could be done but it would be time consuming and to be honest although 200quid is way more than i wanted to spend the time it will save will be worth it.

So i'll be going the same as everyone else. A wideband controller and sensor wired into the megajolt aux input.