Idle AFR

[Sassimac]

Hello All...

I am hoping the VersaTune Brains can help me solve this oddity.

Normally, my car will idle at 14.81:1 on my Dashhawk. It is almost "religious." With nearly all the tunes I have been experimenting with ( and I'm up to 14 ) the AFR stays at this level on idle. Oddly, the last test file and this one start at 14.81:1 and creep to around 14.46:1. Actual driving AFR's are exactly where I have set them, just idle is a little richer.

Any ideas on what to look at...????

Thanks.

[mituc]

At idle the AFR's may bounce between 14:4 and 15.1 and it's because the A/C compressor kicking in an letting go. So you're basically experiencing an engine braking from like 700-750rpm down to idle 650-670 (the RPM values may also be higher if the engine is colder). So I'd say don't worry.
Eventually turn the A/C off for a minute and see what happens. It should stay between 14.5 and 14.8.

[skiptownmcat]

I always show 14.61:1 with dashhawk even though it should be 14.68.

[Sassimac]

Hi All...

I find it really odd that the AFR has become a little rich. I have been running stock files and tuned files for literally a few years now and rarely has the idle AFR changed from 14.81:1. Naturally the aircon will alter things for a bit, but even then the AFR will settle back to 14.81.My fuel economy at the moment is actually sensational. So this has really had zero impact.

It just seems odd that it has changed, and I wonder why.

Steve, have you investigated the idle code at all..??

[mituc]

When the engine is cold the ECU may run richer AFR's AFAIK.

So if you're looking at the AFR's and the engine coolant temp is not at least 75C or so (ideally you should have driven the car for at least 20 minutes) then we can't blame the tune in any way.

[Steve @ VersaTune]

Are you logging desired AFR and actual AFR? How close are they? A lumpy MAF cal could possibly cause it. AFR should flow like a sine wave above and below the target. That is a sign of normal O2 sensor feedback.

[Sassimac]

Steve...

I have not done a MAF cal at all. Those tables remain 100% untouched. And aircon is off. Whether the engine is cold or running temp, makes no difference.

This current tune is using the exact same fuelling as the previous one I built. And the same condition exists. A slightly rich idle. I have also noticed that when I first installed this current tune, AFR's for idle were exactly back to 14.81:1. and over the course of 250km (same tank of fuel), the idle has richened to 14.46:1.

Now I will say, my economy is staggering compared to what I used to get. So, I can't say anything is suffering here. It is just really odd behaviour, that I would like to understand.

Looking at a log I took from the previous tune (identical fuelling), Actual and Desired are nearly always very very close. I am talking almost always well within 0.02 Lambda, if not 0.01.

[Sassimac]

Hello All...

Considering that Desired and Actual are very close, what would cause the ECU to target an AFR under the target set in the CL table? I request say 1.015 Lambda, but the desired and actual AFR are both under Lambda 1.00.

Thanks..!!!