Lean spikes commanded vs actual AFR

[Whippled 496]

Also, I use AFR not EQ. So basically the higher the number, the quicker the return right? If my commanded was 12.0 and i had say 2.7 in my cell, that would put my back to 14.70 very fast. Is an extremely quick transition like that the best method or should be a little longer?

[dc_justin]

Also, I use AFR not EQ. So basically the higher the number, the quicker the return right? If my commanded was 12.0 and i had say 2.7 in my cell, that would put my back to 14.70 very fast. Is an extremely quick transition like that the best method or should be a little longer?

AFR is derived from EQ ratios in the software. A step size of 1.0 is plenty sufficient and will allow you to richen up to as much as 7.35:1 in 1/20th of a second.

[billyjo]

I made the changes that Justin reccomended and it looks like it made a big difference when I slowly transition to boost but when I do a quick stab of the pedal I'm still seeing the spike.

I'm also wondering if the fact that I have a manual transmission vs an automatic makes any difference or is compounding my problem. My thinking on this is when I'm down in the lower RPM ranges I just create more load with the manual where as an auto would shift to a lower gear.

Is the answer to modify my VE table in these areas so that there is a huge spike? Or would commanding a richer AFR ealier help to alleviate some of the problem?

Thanks,

Bill

[hquick]

I know this is like a year old guys but I just dug it up and have a couple of questions. Firstly...I just changed my PE fig's to the same as Justin has posted in this thread. Looking forward to trying them tomorrow.
I was/am having the EXACT same issue as Jaybo.
OK...the question:

A step size of 1.0 is plenty sufficient and will allow you to richen up to as much as 7.35:1 in 1/20th of a second.

Where does the 7.35:1 come from? I sometimes get AFR's of 10 +/- and I don't command it. Where does it come from?

Thanks
__________________

[dc_justin]

I know this is like a year old guys but I just dug it up and have a couple of questions. Firstly...I just changed my PE fig's to the same as Justin has posted in this thread. Looking forward to trying them tomorrow.
I was/am having the EXACT same issue as Jaybo.
OK...the question:


Where does the 7.35:1 come from? I sometimes get AFR's of 10 +/- and I don't command it. Where does it come from?

Thanks
__________________

The 7.35 was just a reference of how quickly PE mode could richen up to that point. In stock trim, it can take a few moments for it to transition from stoich to your PE AFR.

The AFRs in the 10s that you're seeing is occurring when you let off of the throttle when you're in boost, right?

[hquick]

Thanks Justin,
it actually seems to occurr when I get on the gas.
I'll pay closer attention this morning in a few moments on the drive to work.
I'll post my log in half an hour or so.

[hquick]

Here's my current tune and log if you guys don't mind having a look?
Thanks

[dc_justin]

Haven't looked at the tune, but looking at the log, everything looks typical. Best I can tell, it's due to some sort of fuel evaporation/boiling off of the intake runners.

The part that scares me more is the 18:1 AFR spikes as you (and all other 2 bar positive displacement guys) jump into boost.

On a side note, I may be in your neck of the woods for a day in March. Wife has to spend 5 or 6 days in Canberra and I'm going to try and tag along.

[hquick]

Thanks Justin.
Hey...if you make it over here and can get down to Melbourne...we could hook up for a beer.

[hquick]

Here's a log I just took on the way home.
Still getting the lean spikes...and you're right Justin...the AFR's of 10+/- are mostly as I let off the pedal.
1's mark some slight bucking.