AFR Values - Verdict?

[iani]

Having finally found an SD card that would work in my LM-2 AFR gauge, I took the car out for a run tonight and recorded some parts. Ignore the RPM figures, I only have an inductive clamp at the moment and it talks nonsense once on the move.

Session 1 40mph - 76mph under medium acceleration

Session 2 60mph - 70mph, reasonably steady

Session 3 slowing down to take 360 on large roundabout, car goes rich then move off again

 

What are your views, too weak at higher speeds I think

 

 

Edited July 26, 2018 by iani

[scousegit]

Having finally found an SD card that would work in my LM-2 AFR gauge, I took the car out for a run tonight and recorded some parts. Ignore the RPM figures, I only have an inductive clamp at the moment and it talks nonsense once on the move.

Session 1 40mph - 76mph under medium acceleration

Session 2 60mph - 70mph, reasonably steady

Session 3 slowing down to take 360 on large roundabout, car goes rich then move off again

 

What are your views, too weak at higher speeds I think

Can you explain this in plan English please?

[peejay4A]

Looks like there’s a missing attachment.

[iani]

Looks like there’s a missing attachment.

They should be there now.

[Peter Cobbold]

Session 3 shows rich then lean spikes upon closing then reopening throttle, explained here:

https://supertrarged.wordpress.com/2013/06/12/the-lucas-pi-lean-spike/

 

Peter

[oldtuckunder]

Having finally found an SD card that would work in my LM-2 AFR gauge, I took the car out for a run tonight and recorded some parts. Ignore the RPM figures, I only have an inductive clamp at the moment and it talks nonsense once on the move.

Session 1 40mph - 76mph under medium acceleration

Session 2 60mph - 70mph, reasonably steady

Session 3 slowing down to take 360 on large roundabout, car goes rich then move off again

 

What are your views, too weak at higher speeds I think

 

 

 

Having spent a number of years permanently data logging AFR's with an LM2, the first thing you realise and its the next toy you will add is that you want a TPS trace as well, as without it its hard to tell if the engine is working hard or on a trailing throttle. And looking at a trace later like this later it hard to work out/remember exactly what you were doing.

 

I always found the inductive clamp to be the most accurate with an LM2, going from the coil with them can be iffy. So check the cable routing and where you actually have the clamp.

 

As a brief observation your nicely pulling down to 12.5 when you boot it, with it gently rising to 13.5 which I'd say was fairly good, when you get beyond that and the AFR's lean, without knowing what the throttle is doing its hard to judge as if your easing of on the throttle and there is less load on the engine higher AFR's are fine.

 

I have no objection to the Vitesse cruising quite quickly with AFR's in the 15's if I'm hardly touching the throttle, provided as soon as I make any demands they drop straight back down to 12-13 range.

 

When I'm logging and trying to sort things out, I always have set pieces of road where within limits I can repeat exactly the same driving steps, like knowing that I'm going to idle up to set point in a specific gear and then accelerate WOT until I hit a specific RPM and then change, or I'm going to do a WOT pull in 2nd & 3rd until I hit a specific speed. Makes it easy to compare results later.

 

NB. Its far far easier to test going up a hill than it is on the flat, speed rises more slowly so every event lasts longer, you don't run out of road or the legal limit as quickly, and you tend not to relax your foot on the throttle as much on a hill as everything isn't happening quite so frighteningly fast And the engine doesn't mind, load is load. As soon as I started logging TPS I realised that a lot of what I thought were identical sessions weren't and that 7/8th throttle can give way different results to 8/8th's.

 

Unfortunately you have just fallen in to a well of grief and pleasure, once you start acquiring knowledge about what's happening, you realise that you need even more information and data points to really get a handle on it. Never mind the LM2 has 5 aux inputs so you can wire in a lot of telemetry.

 

Alan

[iani]

Thanks Alan & Peter, very useful insight. I guess I’ll have to investigate fitting a TPS now :-)

 

Ian

[TriumphV8]

A lot of work! Do not underestimate!

 

 

By the way, PI measurement is simlar to Speed/density,

with the TPS help you log Alpha/n, that is not the same.

Edited July 27, 2018 by TriumphV8

[oldtuckunder]

A lot of work! Do not underestimate!

 

 

 

Getting on the end of the spindle on a PI car I suspect isn't easy without custom making a spindle, whereas its easy on carbs. If I was going to do it on a PI I think I;d look at using a string potentiometer around an existing intermediate shaft. As long as you can get approx 2V movement for rotation LM2 will expand to full 5V range for logging/display.

 

Alan

[Peter Cobbold]

For simplcity, I'd measure three conditions

1. 60 mph level cruise, as that is the most used when driving. AFR ideally lean around 15-16 fro best mpg. BUT PI usually has to be set richer to avoid pinking upon flooring the throttle.

2 Full throttle 3000prm, region of max torque and acceleration. Rich AFR 12 to 13

3 Fast upward gear change: the lean spike can lead to pinking due to fuel fractioantion. The faster evaporating fuel fraction is low in octane.

Difficult to predict acceptable leaning, listening for pinking probably more informative than AFR reading.

Peter

[Tim D.]

The other signal you can use instead of a TPS is inlet manifold pressure. This then relates directly to the signal that the PI is "seeing". Your traces look good to me. I did a load of AFR logging with my PI before I fitted the supercharger and like others I set up some standard runs to allow comparisons. Definitely worth doing.

Cheers

Tim

[iani]

The other signal you can use instead of a TPS is inlet manifold pressure. This then relates directly to the signal that the PI is "seeing". Your traces look good to me. I did a load of AFR logging with my PI before I fitted the supercharger and like others I set up some standard runs to allow comparisons. Definitely worth doing.

Cheers

Tim

Thanks Tim, did you use a MAP sensor? if so, which one and how as it fitted?

[Tim D.]

Yes. I bought a generic one from eBay that also did boost (to cover the supercharger). As far as I remember it needed 12v and ground and gave a signal from 0 to 5V. My AFR had a 5v sensor line in that I used.

Cheers

Tim

[oldtuckunder]

For a non turbo, you need a simple 1 bar MAP sensor, the Peugeot / GM ones are cheap and work fine, lots of online references to help in using them. I found I needed to give it a 5V supply as the LM2 has no out power supply, however a quick ebay search will provide a solid state12-5V converter for a couple of pounds.

 

Go for a remote one with a pipe input, way easier to mount where you want, and also allows you to experiment where you take the signal from.

 

Alan