The drive: You need to find an empty road free of most traffic. Click the start button on VEAL. Get the engine up to third gear or so. Lock in an RPM that matches a fuel column on the screen. For example, 2600. You should see a cursor highlight on the load cell at this RPM value. Use the screen value and then reference to the car tach value. Now, use your left foot to load the engine; this means depressing the brakes while driving. As the brakes slow down the engine, give more throttle. Balance the amount of brake and throttle to hold that rpm. Keep adding brake effort and throttle effort until you get to WOT (Foot on floor). If you can watch the screen in peripheral vision, you will see that the fuel will adjust the rpm column around 2600. If you do this slowly enough you will have enough datapoints to have the AFR match the target AFR. Now, repeat for the next rpm band 3100. Keep working your way up the table. Don’t forget to pause and let brakes cool between columns. ( good)
Below is a datalog trace of this process. The RPM (white line) is pinned at 2600 +/-50 rpm. The load (green line) is the MAP signal and it goes from 70kPa cruise to 97kPa WOT. Notice that in the middle of the transition there is a lean peak marked with a cursor. This is exactly why you tune this way. The start of the curve the AFR is pinned at 13.5. At the end of the load run the AFR is pinned at 13.1. Both are as they should be. However, the middle transition between these two points is very lean and needed to be tuned to bring the AFR into a safe zone.
Ref Pic 6
Ultimately, this process will get to be quick. Meaning, it should take 45 sec or so per column. In the example picture above the load run took about 26 seconds.
Use higher gears (4th) for the lower rpms, use lower gears (2nd) for the higher rpms. Keep going until you have covered most of the fuel table. Yes, you have to hit those 6500 and higher spots (you may need to set your max RPM to 7000 in TunerStudio and on your MSD). They should go quick. Then you can click “stop”. When done, make sure to hit “apply” and ‘Save to Controller”. Now “save as” a new tune file. I always use Save As because it time stamps the file. It is easier to go back compared to “current tune”. I never know if I am current or not. (good)
After this process of using the computer tune for your process you should review the VE table. Often manually smooth the table in between tuning “runs”. This allows me to fill in areas that I have missed or areas the computer does not interpret correctly. What does manually smooth mean? The fuel table should look like a very smooth waterfall. If you have jagged peaks, valleys or other abruptness in the fuel delivery, this is not correct. This is usually the sign of something else wrong. Could be the process, Could be the setup, Could be the operator.
Now we move on to the “pulls” Start VEAL again, Do some WOT pulls. I usually use 3rd gear for these. Go all the way to the rev limit. HMM. Did you set the rev limit correctly? This should be part of the initial configuration. Below is an example of an RPM pull. If you look at the data trace you will see the white lines with linear upsweep to a maximum value (redline). You will also see the following trace on the VE table to the right with a quick vertical upsweep followed by horizontal taling as the engine reaches maximum load and the rpms are climbing. We can also follow along the AFR and see that it goes super rich at the point of the cursor. This means there is more adjustment to do in the fuel delivery table.
Ref Pic 7
Now, change the cell change Resistance to “normal’ and repeat. And then change to “hard” and repeat. At this point the car should be driving very smoothly with no major rich or lean spots.
Ref Pic 8
At this point you are ready for the fine tuning process. This involves the datalog function and data analysis. I find that this method gives a smoother running engine in the low- mid- load ranges.
After some initial tuning runs I will review datalogs and look at how the fuel is scaled. Megasquirt will run a VE table but this is not actual VE calculation. It is a math number to calculate injector pulse width. The challenge, especially with ITBs is they are often so efficient that you may run out of room in adjustment. Remember we said we would revisit resolution in the table? To Quote from Independence Day. “hello Boys, I’m BAACK!”
Identifying problem areas using the datalog can be very useful. With some practice you will start to use these logs and almost become obsessed. For example, the MAP signal in the picture below has a sawtooth pattern. This is a tell-tale pattern for “my ITBs are not balanced”. So, go fix the hardware. And yes, it was fixed. Some of you paying attention may see the same pattern in a previous picture. How astute of you to notice.
Ref Pic 9
