AFR table vs. gauge readings

[flatbill]

Megasquirt II V3 2.891 Throttle body

I have been working with tuning the VE table and I thought I would try messing with the AFR table. I was surprised to note the the AFR reading at the bottom of the map screen "red" does not match the AFR gauge on the left side of the screen, even after hitting alt B. The gauge seems to jive with the afr gauge on the front dash board on MT. These gauges seem to both run richer than the maps indicate. Is there something I'm missing here? Thanks, Bill

[flatbill]

More info. I would think that the green readings that are supposed to be the "dot" readings would agree with the afr gauge. Mine doesn't. What's up. Bill

[Bernard Fife]

Bill,

Are you referring the the red and green AFR "leds" on the front page? They are configured separately from the AFR gauges. This was done because people had different preferences for how this should be configured.

Note that many of the variables are represented on the runtime, tuning, and front pages, and you may need to set additional parameters to get them all to look the way you want. For example, the EGO display on the front page is set in this section:

[FrontPage]
#if NARROW_BAND_EGO
egoLEDs = 0.0, 1.0, 0.5 ; Voltage settings.
#elif LAMBDA
egoLEDs = 1.5, 0.5, 1.0 ; Lambda settings.
#else
egoLEDs = 19.7, 9.7, 14.7 ; Afr settings.
#endif

The numbers are the left end value, the right end value, and the stoichiometric point where the leds turn from red to green.

This is here: http://www.megamanual.com/mt28.htm#installgauge

However, the leds on other pages are not configurable, I believe. It is 'hard-coded' into MegaTune, and not user-configurable. If it bothers you you should ignore it, or move to TunerStudio.

Lance.

[flatbill]

Lance, Thanks for the reply. No, not the "led's". What I am refering to is this.

When I am in the afr table that is used to tweek the afr up or down ( the lumpy map of MAP vs rpm ) there are 2 lines of text at the bottom of the screen. One line ( red text ) refers to the "cursor" (the red X on the lumpy map) that indicates where you are on the map to adjust it by doing the shift up or down arrow. The other line of text (green) is where the "dot" is and that refers to where the engine is actually running, the MAP and rpm of the motor.

Now, on the right end of the red and green text is an air fuel ratio. I would think that the afr shown in the green text should be the same as the afr shown on the round afr gauge that is on the left side of the screen. In my case these 2 readings do not compare. It seems that the round gauge on the left is usually more rich than the "dot" readings. Shouldn't these be the same?

When I then get out of the afr tuning screen and look at the afr gauge on the main dashboard it seems to be the same as the gauge on the tuning afr page. Usually the gauges read richer than the "dot". Maybe I'm just not seeing this right. If I go to the tuning afr screen and set the idle speed/MAP area to, say 13.5 afr, then do alt B, shouldn't the gauge on the left and the gauge on the main dashboard show something close to 13.5?

I have the ego authority set to zero.

When I start the engine there is a time when the afr is quite rich, like 9.5 for a time, then it leans out to maybe 11 or 12. I assume that this is the after start enrichment. I suppose I need to cut this back some.

Here's another thing I tried. I drove the car, did a datalog. Then I reviewed the data log and looded at areas were the afr was really rich or really lean. Then I went into the VE table and pushed the VE values up or down to adjust the VE. This seemed to help make the motor run better. Then I tried adjusting the afr table and I noticed the differences between the screen and the gauges.

My next thought was to try to do what I had read in some of the posts about adjusting the afr table at idle to max out the MAP at idle. I was going to use the tuning afr and watch the MAP gauge to get there.

Sorry for the long post, but do you think I should try to use the auto mix control? If this does what it sounds like it would do it would certainly get me, at least, closer to really right.

Thanks for any help you can give. Bill

[Bernard Fife]

Bill,

Okay, I got you now!

The gauge is showing you the current AFR of the exhaust gases according to the wideband feedback (and assuming it is set up correctly, etc.).

The green lettering is showing you the table value at the current conditions. That is, it is showing you the target AFR. The gauge will only match this if the EGO correction is enabled and has sufficient range to get to the target level. Since you have the authority set to zero, you wouldn't expect them to agree.

The red lettering is showing you the AFR from the table at the currently selected table position (i.e. the AFR of the table target value as you move around the 12x12 table). This is the table's target AFR value that will be adjusted if you choose to do that. It will be the same as the green value if the cursor is moved to the current operating conditions.

So the gauge is showing you what you are getting, the green is showing what you are aiming for, and the red is showing you what you will change if you use the shift-up or shift-down arrow keys.

Lance.

[flatbill]

Lance, Great info.

I guess my plan now is to review the afr table, decide on what I want my afr's to be ( based on setting up the diagonal values from low kPa/rpm to high kPa/rpm ) then blend in the higher and lower values.

Now, if I set up the target afr's and the WB sensor cannot get to the target with the ego authority set to about 10% I should go to the VE table and adjust the area of trouble. Does that sound right?

When I try to max out the MAP at idle, is it best to adjust the VE or the afr in the area of idle?

Great help. Thanks, Bill

[Bernard Fife]

Bill,

I set my EGO 'active above rpm' well above my idle so that the EGO correction does nothing at idle. Then I tune the VE table to get the minimum MAP kPa at my desired idle speed. So then I know that's the right amount of fuel (because MAP is minimum). The wide band AFR gauge will show what the actual AFR is at that minimum, and I note that value and put it into the AFR table.

At that point you can lower the 'active above rpm' if you like, and the AFR should go to the value you determined that was optimal with only a small amount of EGO correction. However, I rarely do lower the active above rpm - I find that open loop idle is often more consistent and stable.

Lance.