XU10J4RS Idle AFR

[jammapic]

Hi all,

Been doing a bit of data logging just trying to smooth the last few lumps out in my GTi-6 throttle body setup, before moving on to bigger cams, injectors etc.

Where do you guys aim in terms of Idle Air fuel ratio?

If I connect up the Lambda sensor, obviously it sits at 14.7:1 as measured with my wideband - but it idles like crap there with no ICV, missing and stumbling a bit.

With the Lambda disconnected @ 3.0 bar fuel pressure and my chip wizards mapping I see around 12 - 12.5:1, it idles much better but still the odd stumble and pretty "fuelly" smelling.

If I take a little fuel out and shoot for 13:1 it idles smooth as silk, I can adjust the rpm down to 850 and no issues... but it still feels pretty rich.

Any input?

Ta,

JP

[tenwierdufos]

Are you trying this with the engine warm or cold?

I would expect about 12:1 to be fine when the engine is cold, otherwise it probably wont start, but once the engine is nicely warmed up you should be able to get a lot closer to that 14.7:1

[jammapic]

When it's warm mate... when it's cold it gets down as far as 10:1!

[Ruan]

I would expect it to cycle around the stoich mark once fully warmed up and gone open loop..

You should see it cycle above and below stoich as it trims with the Lambda...

But it does have to be up to FULL temperature to go open loop - before then - look at your map and see where it's sitting?

[jammapic]

I would expect it to cycle around the stoich mark once fully warmed up and gone open loop..

You should see it cycle above and below stoich as it trims with the Lambda...

But it does have to be up to FULL temperature to go open loop - before then - look at your map and see where it's sitting?

Don't run lambda mate, it's crap for drivability with the bodies on. No idle control either.

'6 engines seem to like to sit a touch rich at idle from my findings.

JP

[Ruan]

Is the the new map that's on there designed to run alpha-n? Or are we switching to default values? I.e. Did Wayne say - that's how it SHOULD run, or are we finding that it's running better with no Lambda?

I assume you don't have a MAP sensor on there...

[jammapic]

He said run it with no lambda connected as they tend to run better, i.e don't "surge" pulling fuelling up and down.

No, no Map sensor.

[Ruan]

Right, so pure Alpha-N - then I'd say that's pretty normal - what happens if you bump the fuel a little and get to 14.7:1 without the lambda - the Lambda is probably causing other things to happen, it may be pulling the timing around also - I don't know exactly what goes on inside the ECU as far as what adjustments it'll make from the Lambda...

Out of interest, when it's cold and the Lambda is connected, does it stumble badly? Since it's not open loop, so shouldn't pull the fuel around at all - just run off it's speed-density maps.

[jammapic]

It's the same around 14:7 without lambda. It's not very happy round there.

Yes, it stumbles the same when it's cold with the Lambda connected. It doesn't use lambda when it's cold - if you watch the AFR with it plugged in, you can see it suddenly jump from ~12:1 - 14.7:1 when it switches on.

I think I'll take it back to Wayne. It was mapped on a 25*c hot day... it doesn't understand this cold snap!!!

JP