Help me diagnose a change in AFR

[1950StangJump$]

2008 Mustang GT with Kenne Bell Stage 1, Kooks Longtubes, high flow cats.

In Nov 2017, I had it dyno tuned. The tuner set air/fuel at 11.7:1 at WOT. A few months later, I installed an Innovate wideband sensor and ran it to an Aeroforce gauge. It confirmed 11:7:1 at WOT.

So, I set the Aeroforce in scan and didn’t pay much attention to AFR this last year. In the last week, I started paying attention to it again, and it gets down to 11.1:1 at WOT.

The changes in the last year since the dyno:

1. Pulled the Autolite plugs put in by the previous owner and installed Brisk. The old plugs were at .045 gap. At the tuner’s recommendation, I did the Brisk at .035.

2. Installed MSD plug coils.

3. T56 Magnum with RST clutch.

4. Went from 3.55 to 4.10 gears.

5. Upgraded the HE and intercooler pump.

All other changes are either cosmetic or related to the brakes and tires.

What I’ve done to diagnose:

1. I recalibrated the wideband sensor. No change.

2. I put the OEM coils back on. No change.

3. I pulled the Brisk plugs, cleaned, inspected, and reinstalled. No change. They looked great with no evidence of running rich. The tailpipes are not sooty.

The car feels like it always has. I considered the gauge might just have gone faulty, except that it hovers around that magic 14.7:1 ratio when cruising or idling.

I’m starting to wonder if I’m going to have to pay $500 again to put it on the dyno again.

 

[Juice]

Have you cleared KAMs? I would do that first. Either with a handheld or battery disconnect. I your AFR returns to 11.7, then your tune needs a revision.

I actually have a similar issue I'm trying to solve. AFR richens up after driving a few hundred miles.

 

[1950StangJump$]

That’s new to me. Can you expand on KAMs and the need to clear them?

EDIT: I don’t think that’s it. I have also loaded the tune up several times in the last week playing with the “revs per mile” so that I can get the speedo right. A fresh install of a tune (I have several versions with minor variations) makes no difference .

 

[Juice]

KAM Keep Alive Memory, and if you reloading the tune does reset it. So that's probably not it.

 

[RED09GT]

Have you run a free air calibration on the sensor?
Worth a try.
http://blog.innovatemotorsports.com...ration-what-is-it-and-why-is-it-so-important/

 

[1950StangJump$]

Have you run a free air calibration on the sensor?
Worth a try.
http://blog.innovatemotorsports.com...ration-what-is-it-and-why-is-it-so-important/

Yep, as stated above, that was the first thing I did. Doesn’t mean it’s not lost accuracy, I suppose

 

[Dino Dino Bambino]

An AFR of 11.1 at WOT in a FI engine might be a little rich, but it's also safe so I wouldn't be concerned about it.

 

[1950StangJump$]

An AFR of 11.1 at WOT in a FI engine might be a little rich, but it's also safe so I wouldn't be concerned about it.

Yea, I agree. More curious why it “moved” than anything.

I don’t track it, so leaving some HP on the table isn’t the end of the world. Like I said, the plugs looked good, and the tailpipes are clean, so no signs of running rich to an unhealthy extent.

The tuner left it unlocked for me, so I could use the SCT handheld to adjust AFR at WOT. But, I don’t want to lean it any in case it’s just the gauge/sensor that is off.

 

[1950StangJump$]

Is there any chance that going from the Autolite plugs at .045 gap to the Brisk at .035 would change the AFR?

 

[sportinawoody]

I had a car once throwing p0171&p0174( both banks lean). After 3 days of diagnosis and coming up empty,I changed the plugs because customer had just put in new bosch’ and boom. Stft’s went from -30 to 0. Try putting the old plugs back in and see if it straightens out

 

[06monera96]

o2 stop working?

 

[RED09GT]

Did your fuel supplier switch something up? Perhaps they were blending a higher amount of ethanol when it was being tuned and have now either reduced the amount of ethanol or got rid of it altogether?

 

[1950StangJump$]

The O2 could be bad, but I doubt it. They AFR seems accurate otherwise.

The fuel blend thing is an interesting thought. The only difference would have been that it was tuned with the winter blend, and now we are on the summer. Never heard of that mattering though

 

[sportinawoody]

Try swapping the plugs back and watch your short term trims. This pid will tell you if you’re lean rich or comfortably in the middle

 

[1950StangJump$]

Try swapping the plugs back and watch your short term trims. This pid will tell you if you’re lean rich or comfortably in the middle

Unfortunately, I threw the old plugs out.