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Tuning Maps and Basic Engine Calibration
Okay, now that we have covered all of the basic components that make up the fuel injection system, and the simple physical properties of nature that we use to operate the engine, we are ready to begin the process of calibrating the software to run the engine properly. This is a time-consuming and tedious process, so don’t get in too much of a hurry to get it all done, especially if it is your first time tuning an engine.
In this chapter we’ll take a look at some of the practices and equipment for properly tuning an engine. Many tuners in the performance aftermarket prefer to use a chassis dynamometer such as the one shown here to calibrate an engine.
Consult a professional when looking for advice. There are all too many people willing to give out free advice about how everything in the world works, but remember that few hot-rodders have successfully tuned their own fuel-injected engines, and there is a lot more to it than meets the eye. This book will serve as a great reference when questions come up, but nothing can take the place of the experience you’ll gain from jumping in there and getting your hands dirty!
Be sure to take great caution when making changes to the program calibration, as it is very easy to get lost and make mistakes. When tuning an engine using EFI, it is quite simple to make a change that could be detrimental to your engine. Always consult the manufacturer’s user manual or technical support group before attempting any changes you are unsure about.
Tuning an engine using software to manage the EFI system will require you to input numbers or values into a variety of maps. These maps each control a certain engine function or operation. Often they work in conjunction with each other and in order to tune the engine properly, so more than one map must be used to get the desired result. Before we begin discussing the actual tuning of any maps, let’s take a brief overview of what the more common maps are and what they do.
Base Fuel Map
The single most common map that will be tuned in any engine is the base fuel map. This map consists of a grid matrix of values that the computer uses to look up the correct amount of fuel to add to the engine under any given operating circumstance.
All of the engine’s basic fueling requirements are taken from this table. Any adjustments for temperature, altitude, or for special circumstances, like for use during cold starting, are made against this map, so it is important to always tune it first to avoid chasing one’s tail later on. Typically, this map shows the engine’s volumetric efficiency, or how much air the engine is using at that exact moment.
The single most common map that will be tuned in any engine is the base fuel map. This map consists of a grid matrix of values that the computer uses to look up the correct amount of fuel to add to the engine under any given operating condition.
The base fuel map shows the engine’s VE on a two-axis grid. One axis represents the engine speed, and another represents engine load. In this case, the most often used unit for load is MAP or manifold absolute pressure. The computer uses information from the MAP sensor to determine how well the engine is filling with air, and compares that value to the engine speed to see how many times it is filling in a given period of time.
The throttle position sensor can also indicate engine load. The more throttle angle the ECU sees, the more air it assumes is entering the engine. The ECU compares the angle of throttle opening to the engine speed to get an estimate of the engine’s volumetric efficiency.
Typically, throttle angle by itself is not used in an engine where boost is present. This is mostly due to the fact that the manifold pressure can change wildly under full-throttle conditions and there is no way for the throttle position sensor alone to register this change. In this case, the MAP sensor is the better choice.
This map represents how much air the engine is using at that exact moment. Normally it does this by having a two-axis grid. One axis represents the engine speed, and another represents engine load. It is usually called either the VE (volumetric efficiency) map or the base fuel map.
When an engine has very radical camshafts or individual throttle bodies, it can sometimes have a very weak or even erratic MAP signal because the overlap period of the camshaft causes pressure to fluctuate in the intake manifold. This makes it difficult to tune the engine efficiently using only the MAP sensor signal. In this case the throttle position signal is the better choice for mapping, because it ignores these tiny fluctuation in manifold pressure and can more accurately control the air/fuel mixture at low engine speeds.
When an engine has very radical camshafts or individual throttle bodies, it can sometimes have a very weak or even erratic MAP signal. This makes it difficult to tune the engine efficiently. In this case, using the throttle position signal is the better choice.
Some ECUs have the capability to use both methods at the same time. This allows unique engine applications, such as a radically cammed engine using individual throttle bodies and turbochargers! This way the ECU can ignore the small changes in manifold pressure at low engine speeds where they are unimportant, yet fully recognize the larger variations in manifold pressure when the engine becomes pressurized from forced induction. Keep this feature in mind when shopping for an ECU to fit the needs of your particular project.
Once you have determined the load scale for the base fuel map, you will generally want to use the same scale for the base ignition map. This will keep all your tuning methods the same and avoid confusion when changing between maps during tuning. The load scale is the side of the table or map that represents how hard the engine is working (how much air it is flowing).
Base Ignition Map
The base ignition map is essentially the same as the fuel table in that it represents the engine’s volumetric efficiency at any point in its operating range. The words “table” and “map” are interchangeable, and both represent the matrix-style grid of numbers for the fuel, timing, airflow, etc. All of the engine’s basic ignition requirements are taken from the base ignition map. Any adjustments for temperature, altitude, or during cold cranking are made against this map, so it is important to always calibrate this map first.
As stated earlier, the same grid and load scale functions used in the base fuel table apply here, so that tuning is easier to understand. This way you can compare fuel and timing values for a given point on the map easily without any conversions.
This map allows the user to adjust the ignition advance as necessary anywhere in the engine’s load or speed ranges. Careful tuning here will result in a very efficient and smooth-running engine. Use caution here, because even small changes in the amount of ignition advance you supply to the engine can have dramatic effects on the margin of safety. It is easy to cause damage to the engine by adding too much advance, so go slowly, and conservatively creep up on the optimum amount to avoid trouble.
Idle Spark Map
This map is used to control the ignition timing while the engine is at idle. Usually this map uses a small grid of engine speed versus temperature, battery voltage, or some other reference point to accurately control the ignition event during idle conditions. The user can fine-tune the engine’s performance by slowly testing different values in this table with trial and error.
The target idle map is also used to control the idle speed via the idle air control valve, or IAC. Once the engine speed is determined, this map uses the values in the table to determine the correct amount of ignition timing and IAC opening to get to the desired idle speed.
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Table of Contents |
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Chap. 1 - Carburetors vs. Fuel Injection |
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Chap. 2 - The Basics of Electronics |
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Chap. 3 - Tools and Equipment |
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Chap. 4 - ECU Inputs |
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Chap. 5 - ECU Outputs |
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Chap. 6 - Tuning Maps and Basic Engine Calibration |
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Chap. 7 - ACCEL/DFI |
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Chap. 8 - AEM Plug & Play |
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Chap 9 - Autronic |
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Chap. 15 - Holley Commander 950 |
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Chap. 16 - MoTeC |
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Chap. 17 - Simple Digital Systems (SDS) |
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