Road Tuning Techniques
Let’s now talk about the fun part - Driving the car. I mean, this is why we all bought them. And completing an EFI install just makes them better. Above I have described most of the background that is required to tune an engine. Time to put this to practice. Now, I will say that the process of tuning an EFI engine is very similar to tuning CIS, MFI, or Carbs. The same principles apply. Try not to overcomplicate this process, nor overwhelm yourself. KISS.
Now, An engine will be lazy when it's too rich. An engine will misfire, surge and be unhappy when its lean. The idea is to get between these two extremes and enjoy a crisp, responsive, power-producing State of Zen. Think of EFI as tuning with a keyboard instead of wrenches and screwdrivers. You are not adjusting the fuel pressure in the WUR for CIS. You are not removing and resizing jets on carbs. You are not adjusting flyweights or rack stops in the MFI pump. Just a keystroke here and there to match a fuel delivery to an AFR value. Live this mindset and tuning life becomes much easier. Also, the power of EFi is to give the engine what it wants - EVERYWHERE in the operating space.
There are two primary methods to tune an EFI system. Live and Datalog. I will cover both. Let’s start with live tuning.
You have the engine started but need to work on the fuel VE table. Often you need to get the engine to idle on its own. Remember our discussion about the fuel global multiplier. (in the section for fuel delivery ) In MS this is req_fuel parameter. I will raise and lower this parameter (or injector scaling factor in other software) first, before making changes to the fuel table. This is an easy way to add fuel everywhere. Even a base table has a curvature that is close to what is needed to get through the first few steps of tuning. Now, this process of adjusting the fuel global multiplier works really well if you have a starting map from a known good running engine.
At this point the engine should idle on its own. The first step is to turn off all acceleration enrichments. You can do this by setting values to zero or setting trigger setpoints to levels high enough they will never trigger. The purpose here is steady state operation in a very controlled manner. We are not concerned with changing throttle at this point.
The tuning process Starts with no-load fuel sites. In this case, you are simply increasing the rpms of the engine with the car in neutral and sitting still. This will give clues as to how much fuel is required to actually drive. The process is straightforward. With the laptop open, tuning software running and the fuel adjustment panel open, you will slowly rev the engine. As the rpms rise above idle you need to watch the AFR. This early in the game it is doubtful that the engine will perform at the target AFR. So, you will need to manually adjust the fuel trim until the AFR is in range. We are targeting 13.5 for this exercise. Slowly raise the rpms while adjusting fuel all the way up to approximately 3500 - 4000 rpm. This will create an arc shape across the VE table. In the example picture below the no load points are marked with yellow.
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Now, most VE tables have some indicator of what has changed. MS shows red/blue as you change fuel, They also put a yellow marker dot in the corner of changed cells. AEM changes color, Motec puts a red marker on the VE map. Either way, Look at your changed cell range and then compare to the adjacent cells. There is usually a consistent shape to the changed cells being higher or lower than the adjacent cells. The goal now, is to blend the adjacent cells to match the ones you changed based on actual AFR feedback. Meaning, If your no-load arc is lower than the surrounding and adjacent cells you must lower the rest. If the no-load arc is now higher than the surrounding areas you need to raise them up to blend.
Here is the same fuel table after blending. I raised up the rest of the table to match the no-load sites.
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Actually tuning the engine. The following process allows you to to drive in a certain pattern while datalogging. Then analyze the datalog and make adjustments.
The tuning process of the the fuel tables is for steady state conditions. In this case, we are not concerned about transitions and therefore these transition corrections must be turned off. This will allow you to setup a more accurate tune. So, Make sure you turn off AE Correction. To turn off AE, set the TPS or MAP threshold under “time based AE” as high as possible. I think 1000 is the maximum. Make sure you also have EGO correction turned off. Now, this means the car may be temporarily difficult during throttle transitions. This is normal. We have to tune the transitions after the car is running.
Many ECUs have an auto-tune function. It is useful to get the car up and running where you can drive and have the computer adjust the mixture for you. In this example I will use the tuning functions for Megasquirt. Let’s define this process. VEAL stands for VE Analyze live. It is also called VE Analyze live. It is not called AutoTune even though most people refer to it as such based on the functional name. EMU Black also has an auto-Tune function. AEM has a datalog conversion macro that runs in Excel for fuel trim adjustments. Motec has a key command to correct fuel trim at each individual table cell. They all work by taking the actual AFR, comparing it to a target AFR, calculating a percentage offset between the two and using the offset to adjust fuel trim up or down as needed. Of course, there are error tolerance and other correction factors involved so that the PC doesn’t make too many mistakes.
Once the car is warmed up you can select the tab for Tune Analyze Live. Then click the Advanced settings tab on the right side. Use the filters to block out certain parts once the car is running well; select a range of cells and then right click to lock them from any changes teh software may want to make. For example, once the car idles, block out the idle cells (for example, min RPM 1100). Also, start with the “Cell Change Resistance” pull down menu to Easy to start with. Now you are going to drive the car.
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