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Inside The Black Box (Part 1) from MM&FF Magazine
Understanding and Tuning Your Ford EFI System


Some of use have been there. Others never have. For those who have seen the inside, we realize it’s a scary and confusing place. We slowly found our way around the “safer areas.” than ventured further as we felt more comfortable. Still, years later, there are unknown caverns where we fear to tread. The place we speak of does not exist in the physical world - it’s a virtual one. We’re talking about the world of the Ford Electronic Engine Control system.

Not too many years ago, the means to get inside and reprogram the Ford Electronic Engine Control (or EEC, pronounced eek ) system was reserved to few who possessed the specialized systems and electronic engineering knowledge to read and “reverse engineer” the Ford EEC system. But in this day and age, in addition to several stand-alone electronic engine control systems (that totally replaces the stock system), there are many aftermarket systems available with the ability to reprogram your existing Ford EFI system, either through an add-on chip or by reflashing to stock processor.

In this three-part series, we’ll give you the background info on how the EEC systems work. In part 2 we will discuss simple tuning specifics (as far as the Ford EEC system parameters go), while in Part 3 we’ll go through some actual tuning techniques (again, very much simplified). In the end, you’ll hopefully understand what your hired tuning expert is doing.

THE SIMPLE EXPLANATION

The Electronic Control Unit (ECU, aka Powertrain Control Unit or PCM) is the brain of the entire EEC outfit. It uses various sensors to “see” current running conditions and understand driver demands, then makes decisions and perform calculations based on its internal programming (on board memory). Finally, it sends electronic outputs to a host of actuators which control the fuel and spark delivery for the engine, emissions control systems, coolant fans, automatic transmission functions, and so on. As EEC systems have evolved and continue to do so, the ECU gains control over more and more variables. In this series, we will focus primarily on the fuel and spark control, since they have the greatest influence on engine performance.

FUEL CONTROL BASICS

Before we go into detail on the three different fuel control strategies, you need to understand the fundamental similarities between all EFI systems. That leads us to the electronic fuel injectors and the EFI fuel system. It’s a simple enough concept. For a constant air/fuel (A/F) ratio, as the airflow into the engine increases (from increased rpm, increased throttle opening, or increased boost, for example), the fuel flow must also increase proportionately. But with electronic fuel injectors, the added fuel flow does not come from increasing the flow through the injectors the same way, as say, the throttle valve increased the airflow by opening the passage in the inlet path. Electronic fuel injectors are actually digital (on/off) devices.

An electronic fuel injector is an electrically controlled on/off valve for fuel flow. When it’s on, it flows fuel in proportion to its nozzle size, and fuel pressure. When it’s off, meaning they are opened and closed quite rapidly. If more fuel is needed, the “on” pulse gets longer. The amount of time the injectors are open is termed Pulse Width.

Or the time between successive pulses gets shorter. This is important, since many people don’t understand how you can flow more fuel with a shorter pulse width. The ratio between injector “on time” and on time plus “off time” (total cycle time) is know as the Duty Cycle, DC. For example, if the PW (on time) is 2.5 milliseconds (ms), and there are 5 ms between injections, the DC will be 0.5 or 50 percent.

Injection events can either be done in batch fire mods, where groups (banks) of injectors are fired at the same time (usually once per engine revolution), or in sequential mods, where individual port injectors fire for their cylinder only, normally following the engine firing order (once every second engine revolution for four stroke engines). Sequential EFI (SEFI) systems have some advantages for fuel control over batch systems (like improved emissions and rev limiting ability), and are therefore used on all modern OEM EFI systems.

For a given injector size, at a fixed fuel pressure, the fuel flow rate will increase directly proportionally to the duty cycle. That is, until you reach 100 percent DC. At that point, the injectors are theoretically open all the time, and fuel flow can’t increase unless the fuel pressure is increased - we’ll get to that in a minute. If you get to the point of saturating the injectors (100 percent DC), you’re a/F ratio will go lean if additional air flows into the engine. Hence the reason to install larger flow injectors. In practice, you typically don’t want to exceed 85 percent, since the injectors can overheat from all the applied current. Also at high DC the injector pulse width can become unstable, and with some injectors, less fuel will actually flow at high DC’s.

So maximum fuel flow will then be limited by the size of your injector, right? Not totally. The other variable is the fuel pressure acting across the injector (from the supply side to the intake manifold side). For a given nozzle size, you can push more flow through with a higher fuel pressure. This is why injectors are flow rated at a specific fuel pressure. It is also why you can get away with smaller injectors when using a Fuel Management Unit (FMU) that’s included in many supercharger kits. The FMU basically cranks the fuel pressure way up under boost to force more fuel through the smaller injectors. It’s really a Band-Aid solution to having properly sized injectors, because the high pressure can shorten the life of your injectors and your fuel pump.

So for a given injector size, we now have two variables to control our fuel flow: DC and Fuel Pressure (FP). To make life easier for the Ecu to control the fuel flow precisely, we’d like to have only one variable, so the FP is fixed at a constant value, typically 39 psi for most stock EFI fords. But if we want constant fuel pressure, why do we regulate it with manifold vacuum in order to maintain a constant pressure across the injector? As intake manifold vacuum increases, the intake pressure decreases, therefore we reduce the fuel rail pressure the same amount to maintain the constant pressure drop across the injector. For boosted applications, we need to do the same thing in the other direction, i.e., as boost increases manifold pressure, we need to similarly increase the fuel pressure (although most stock fuel pressure regulators will not do this). The confusing part is we normally talk about manifold vacuum in units of inches of Mercury (in. Hg), while boost and fuel pressure are usually measured in pounds per square inch (psi). If you do the units conversion, at 15 in. Hg manifold vacuum (idle with a mild cam), we should reduce fuel pressure by about 7psi.

On the earlier EEC cars, the fuel system was a return-style system, where the electric fuel pump in the tank simply pumped fuel at full flow all the time. The (manifold vacuum modulated) fuel pressure regulator then bypasses the excess fuel back into the tank. With the newer returnless fuel systems, it gets a bit more complicated. Now the ECU senses fuel pressure in the fuel rails and relative to the manifold vacuum, and controls the fuel pressure across the injector by pulsing the pump voltage. With this system, fuel is not needlessly pumped around and around, heating up in the process. But it requires a special pump to work with pulsed voltage.

Now that you understand the basics of fuel delivery, you need to understand how the Ecu decides the proper injector puls

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Inside The Black Box, Part 2 (MM&FF Article)
Learning The Ins and Outs of Ford’s EEC EFI Systems


Welcome back for our second look inside the mysterious black box that we can the Ford EEC system. Last month we covered the basics of EFI, with an emphasis on the Ford systems. This month we’ll delve into the specifics of the Ford EEC.

But before we start changing around ones and zero’s in the programming, we need to cover some of the hardware upgrades and the theories needed/required for performance applications. These can include properly sizing injectors, MAF sensors and fuel pumps, big cams, big-port heads/intake, superchargers, low restriction cold-air intakes, free-flowing exhaust, and more. These are all common mods when seeking additional horsepower.

What they all have in common is the ability to stuff more air into the engine. The fuel side is certainly less glamorous than adding a supercharger, for example, but you can’t ignore the fuel side if you want safe, reliable power gains. With more air, more fuel is needed. It’s that simple.

To understand the fuel requirements, you need to first understand Brake Specific Fuel Consumption (BSFC). BSFC is a measure of your engine’s efficiency, and it’s simply the ratio of fuel flow (in lb/hr) divided by the brake horsepower output. Really efficient naturally aspirated gasoline engines run in the low .04 lb/hr-hp range, while richer running supercharged engines can be upwards of .06 lb/hr-hp.

The size of your fuel system, start with a realistic estimate of your BSFC (higher numbers are safer to go with if you’re not sure), and your estimated horsepower output (again, try to be realistic here). Let’s say were expecting 500 flywheel horsepower, and we’ll be running a supercharger. We’re expecting a BSFC of .06. To find the fuel flow requirements, multiply the horsepower by the BSFC to get 500 x .06 - 300 lb/hr. To convert gallons/hr divide by 6.2 to get 48 gal/hr. To get liters/he multiply 4.78 to get 183 L/hr.

Now this doesn’t seem like much, but it’s the minimum fuel flow you need to see at the fuel rails to support 500hp at maximum fuel pressure. Fuel flow drops of dramatically when you crank up the pressure the pump has to push against (keep this in mind if you’re running boost). When looking at fuel-pump flow rating, check carefully how much it actually flows at the fuel pressure you need. Also, keep in mind it’s tougher for the pump to push the fuel forward from the tank to the engine under acceleration, so you always want to size your pump a bit bigger. In the above example, we’d go with a 255 L/hr unit and we should be good.

Regardless of how much math you do ahead of time, it’s always good to either log fuel pressure during dyno runs (newer EEC V), or install a fuel pressure gauge in the car (older EEC IV). If your fuel pressure starts dropping as rpm/hp increases, it’s telling you your pump is undersized, or you have some other restriction in your fuel system. Fix it before it costs you an expensive engine.

For injector sizing, we can use the same math as above to get the fuel flow rate in lb/hr. In our previous 500hp example, we calculated 300 lb/hr. If we have eight injectors, then each needs to flow 300/8 = 37.5 lb/hr. Again, this is the absolute minimum injector size to flow the required fuel at 100% duty cycle (DC). We want a bit of a safety factor, and we’d rather not have to run our injectors at anything more than say 85% DC. So, taking 37.5/.85 = 44 lb/hr, we could use a 42 lb/hr injector here, but we’d end up pushing it to an 89 percent DC at peak horsepower.

Another solution to run the 42 lb/hr injectors at no more than 85 percent DC would be to run them at a slightly higher fuel pressure drop. Since our calculated injector size was 44 lb/hr (at 85 percent DC), we need to increase fuel pressure by (44/42)2 = 1.098, or roughly 10 percent. Taking our 39psi fuel-pressure drop and multiplying by 1.098 gives us about 43 psi. Running a fuel-pressure drop of 43 psi would therefore allow us to run the 42 lb/hr injector safely.

Lastly on the list to ensure adequate fuel delivery is the MAF sensor. Why discuss a MAF sensor when talking about fuel-system capacity? Well, the ECU can accept only 5 volts as a maximum output from a MAF sensor. If you start flowing enough air through your MAF that it outputs 5 volts, the ECU will not “see” that additional airflow and hence not add any more fuel to the mix (i.e. your MAF is “pegged”). This is now dangerous territory, since more air without more fuel equals a lean condition, usually followed by a big BANG!

For our 500hp example, we can calculate the expected airflow at peak horsepower. If we’re targeting a safely A/F ratio of 11.5:1 (for our supercharged engine), 300 lb/hr of fuel flow will correspond to 300 x 11.5 = 3450 lb/hr of airflow. Dividing by 2.2 gives us 1,566 kg/hr. On a 5.0 HO engine, the stock MAF sensor hits 5 volts at 835 kg/hr. You can now see why running the stock MAF calibration would be a problem with a 500hp engine.

In part 1 of this series, we mentioned the aftermarket MAF sensors that were calibrated for larger injectors. The technique was to reduce the voltage output for the same airflow, thus fooling the ECU into thinking there was less air flowing into the engine, so the ECU would calculate a shorter injector PW, and everything should work out without having no reprogram the ECU. The problem with this plan is the ECU load calculations become inaccurate, which could cause other problems.

But a good (and necessary) thing also happens with the larger injectors calibrated MAF sensor approach. While the MAF sensor output voltage is reduced for a given airflow, you can also view it from the other perspective, where for a given voltage, the actual airflow is greater. The result is now a MAF that will measure airflow much greater than the stock 835 kg/hr before outputting 5 volts. For example, 42 lb/hr calibrated for MAF sensors will measure anywhere from 1,700 to 2,900 kg/hr at 5 volts, depending on what size and type.

In many cases, the dynamic range of a MAF sensor is calibrated for larger injectors works out closely with the dynamic range of the injectors themselves. In other words, just when you’re at a horsepower level where you’re running out of fuel-flow ability from a given size injector, you’re about at the limit of measuring the corresponding airflow for a MAF sensor calibrated to that injector size. Installing a MAF sensor calibrated for larger injectors therefore becomes a necessity when forced to upgrade to larger injectors. But how do we get around the problem of incorrect load calculations? Simple, by reprogramming the ECU so it knows the actual airflow for any given MAF sensor voltage, and the actual injector flow rates. If the ECU isn’t being fooled, it will correctly calculate all necessary parameters.

Now that we’ve explained the up front stuff, we can finally fo into the ECU to tune. Keep in mind that you can not tune around a mechanic/physical problem with the engine or fuel system. Doing so will only be a band-aid solution, and usually temporary at best. To get the best idle, part throttle, and WOT performance, you need to have a healthy engine and the proper parts to support the air and fuel requirements.

EEC BASIC TUNING CONCEPTS

In the Ford EEC universe, all tuning parameters are grouped into either “scalars”, “functions”, or “tables”. Scalars refer to one dimensional variables, such as idle rpm, engine cid, and so on, or “switches”, where a feature can be enabled or disabled. Functions refer to two-dimensional parameters, such as WOT spark advance versus RPM. Tables are used for three-dimensional parameters, such as spark advance versus load and rpm.

Again, our focus for this series will be on fuel and spark tuning, with honorable mention on