Ford EFI basics
Last Updated on July 23, 2024 by Mutiara
The EEC thinks in a flow-log which can often be difficult for an average person to understand. So it has to be converted into text and broken up into strategies. A strategy is the arranging and planning of actions with reference to accomplishing a short-range objective. By coming up with several different strategies one can accomplish a long-term goal. This is good information for diagnosing and setting up a good Ford EEC EFI system. By examining data from the EEC it is possible to gain an understanding of why certain things happen and others don’t. There is about 50-200KB of raw data inside the computer that can be broken down into countless different strategies. Try to combine the strategies together after you read it once or twice.
Not all EECs are programmed the same, the following is typical logic for typical engines. Some actual numbers and dividing lines could be different for some models.
Start / Crank
The EEC needs to senses several things to start an engine:
- Power to EEC and fuel pump(s)
- Slow and irregular PIP signal from the distributor
- MAF/MAP low and irregular
- TPS is closed
- HEGO shows lean
Even though the fuel pump can be heard whirring as the key is turned, the injectors don’t release any fuel until the EEC senses engine rotation. Even when the engine does turn over, the EEC hesitates almost a full second to begin fuel and spark, this is to support oil lubrication. ECT and ACT determine the amount of fuel. The colder it is the more fuel is dumped in. The Idle Air Bypass is opened 100% to allow for operator error free starting. Spark control is taken over by the TFI, as long as the key is held in the start position. In the event that things go bad and the ignition system is not able to make the engine fire, and it becomes flooded, all that has to be done is pressing the accelerator to the floor during starting. As a result the full open TPS will tell the EEC to cut the injectors back to almost nothing. Once the fuel has been flushed out, and the pedal is released, the ECC will fire the injectors and allow the engine to start. Once the key springs into run, timing is determined by ECT and ACT, the PIP steadies out, the MAF/MAP builds, and the system bumps into the next strategy.
Cold Start & Warm Up
The engine has just started and needs to get adjusted. The EEC’s first reaction is to keep the throttle air bypass open 100% or else it’ll go back to engine crank mode. RPM will drop however, usually to around 1000RPM after a few seconds, then drop down to base idle as the engine gets warmer (about 160F). The EEC looks almost completely at ECT and TPS, both indicate what will occur next. The colder the more fuel gets dumped in and the more timing added. When the engine gets warmer, (about 170F) the EEC will lean out the mixture. This logic will speed up the time it takes to heat up the engine and converter. If the car begins to be driven under 185F the EEC will jump to cold drive-away strategy. If the car is left to idle the ECT will cross 185F in about 4 minutes and the engine goes into a warm idle.
One shouldn’t be hesitant about driving the car at any time, after all these strategies would not have been created if they were not meant to be used. Driving the car right away is good for economy purposes, cold cars burn more fuel so it’s wise to get them warmer quicker. Although it’s recommended to give it at least a few seconds to ensure oil pressure. WOT should also be avoided until oil reaches the proper operating temperature. This helps ensure a longer engine lifespan.
Cold Drive-Away
So the TPS and PIP are going up, the MAF/MAP is showing greater load, and the ECT is under 185F. The TPS and MAF/MAP tell EEC that the vehicle is now driving away. The goal at this point is to move the vehicle without stalling and warm up the engine as fast as possible. The IAB opens 100% for insurance from stalling if the TB slams shut suddenly. This creates a rich fuel mixture that leans out as temp rises. Once ECT is greater than 170F the mixture is actually less than 15:1, this rushes the engine into normal operating temperatures quicker. Timing is advanced and retards slowly as temps rise. Once the ECT temp crosses 185F the mixture should return to normal and relate to HEGO signal as long as the vehicle isn’t accelerating fast enough to be in another strategy. After 4 minutes if the engine is warm enough to begin EGR function, it’s about time to pass command to the Big-3. Warm cruise, Part-Throttle, and Full-throttle acceleration can take over from here.
Warm Idle
This one tends to be more about emissions. Warm idle occurs if the engine starts and ECT rises above 185F, the vehicle comes to a stoplight, or placed back into neutral. The computer is programmed with a target RPM for idle, typically it’s around 672RPM. Typically the computer is struggling to achieve its target RPM. 255F is the magic number to start complaining about overheating. Fuel is now closed loop with HEGO switching. To achieve perfect emissions the EEC is aiming for 14.7:1 A/F ratio, enrichment will occur only if the ECT is above 225F. There will be no EGR operation at these RPMs. Timing is mildly advanced and will begin to retard after a minute. Hot exhaust gasses are needed to help complete combustion and converter operation. Air is pumped into the converter, but will dump to the atmosphere after several minutes to prevent overheating the converter. The Throttle Air Bypass will be controlling idle, so a nice smooth idle is needed. Not too high with A/T transmissions to prevent creep at stoplights. Idle will increases 100-200RPM if the ECT or ACT is over 225F. This RPM increase will help burn the rich mixture cooling the combustion chamber. The faster RPM speeds up the accessories, specifically the water pump and fan. Belt fans will speed up, and electric fans will need more juice from the alternator.
Warm Cruise
What sounds easy turns out to be one of the most in-depth strategies used. It is assumed that drivers spend most of the time driving at cruise, so the lowest emissions are needed, highest economy, and moderate power at this time. The only good thing of warm cruise is that engine conditions are stable and need the least amount of safety nets. The throttle air bypass is still at 100% in preparation for future braking. Fuel is stabilized with the switching of the HEGO, it cycles about 10-20 times a second. To do this the fuel ratio is leaned and enriched slightly each time the HEGO switches from lean to rich. It’s like a high wire act, balancing fuel for maximum economy. EGR is operational allowing more timing with less fear of detonation. EGR also lowers the amount of oxygen in the mixture by about 15%, thus not requiring as much fuel. The canister purge valve is opened to ingest fuel vapors, this allows us to cut back on fuel metering slightly more and prevents fuel vapors from escaping to the atmosphere. Timing can be advanced to increase engine temperature and counteract EGR influence upon igniting combustion gasses. Timing is used to control engine temps, hotter engines burn fuel more completely. And for the fuel that wasn’t burned in the combustion chamber, extra air flow has to be pumped into the exhaust system. This air with the heat of the exhaust creates further break down of HC, CO, and Nox into CO2, H2O, and N2. The catalytic converter can accept all of the airflow without fear of over heating during cruise. The converter is cooled by air passing under the vehicle.
Full-Throttle Acceleration
The TPS signals wide open throttle to the EEC, this states that the driver doesn’t care about economy or emissions and want maximum power to the wheels. Fuel enriches to a preset level even further the colder the ACT is. The timing jumps up to a maximum preset level around 28BTDC, and this is where the Knock plays a role. The Knock sensor acts as a safety net for the Ford. The factory does not want the EEC to bump the timing to dangerous amounts. If a new vehicle is purchased and timing is added with a chip, this could cause detonation. People do this to get more timing and better performance. So the Knock sensor is there to stop the owner that pushes the motor’s limits with timing for more performance from blowing a ring or burning some valves. The throttle air bypass remains at 100%, providing a larger throttle inlet and as a back up in case the throttle slams shut. All EGR functions are stopped and the canister purge valve is closed to ensure the exact air to fuel ratios desired. Smog pump air is dumped to atmosphere, air conditioning, electric fan, and all other high demand accessories are shut off to lessen the accessory drive load from A/C and alternator. For the safety of the vehicle a rev limiter and a speed limiter is also required, this changes from each model and engine. Basic models are limited to around 6000RPM and 90MPH by turning off half of the fuel injectors. Some Ford engines equipped with factory installed turbo / superchargers include maximum boost control through wastages.
Deceleration
During braking, when the foot is removed from the accelerator, the EEC senses the TPS go to closed and VSS signal slow. This presents a few problems that are easily overcome. First stalling has to be avoided, this is why the IAB has been open, just in case the throttle snaps shut. After throttle closure the Throttle Air Bypass closes slowly closes. Then it controls idle as the vehicle reaches a stop and moves back into warm idle strategy. Emissions and wasted fuel is major concern during deceleration. Therefore the EEC turns the injectors completely off when RPM is over 1500 and the engine is over 140F. Injectors begin operating under 1500RPM or if the accelerator is pressed. If a VSS is present then there is a risk of stalling when slowing down from over 15000 RPM. EGR is turned off but the canister purge is opened to burn off fuel vapors from the gas tank. Timing can be advanced for two reasons, first with low airflow signals there is little chance of detonation. Secondly, advanced timing helps push back on the pistons, this helps create that engine brake effect.
Failure Mode
Failure mode is a stand in strategy in the EEC designed to maintain vehicle operation should one or more sensor inputs fail. When a sensor input is perceived to be out-of-limits by the EEC, memorized data from the computers KAM memory will be initiated. EEC continually checks the sensors against its records of normal readings during operating conditions similar to its current state. Randomly the EEC looks at the past to see if the engine is somewhat where it usually is. If for some unknown reason a sensor is off the charts, it can’t be trusted. So instead of tuning the engine to a possible faulty sensor reading and harming the engine and drive-ability, the EEC replaces the sensor reading with a best guess from a past memory. This is why unplugging the battery to fix something can sometimes create negative results. Unplugging the battery causes EEC to memorize all the sensor data as base line and normal. If it memorizes a bad sensor it will take it longer to call it a liar. Ford did however give EEC a very broad idea of what the sensor should be reading in its permanent ROM memory, so it will catch on to failed equipment sooner.
The sensors will be divided into two groups. Ones that will cause failure mode but allow drive-ability and the sensors that will cause a no-start or barely drive. Actuators can cause failure mode to take over, but only if the failed actuator is giving a sensor reading way off the chart.
Adaptive Strategy
The EEC likes to toy with the fuel ratio at random. It does this to run complex math equations, calculating how much fuel is required to reach certain lean or rich states. Because playing this cat and mouse game with the fuel ratio allows the engine parameters in other strategies to be fine tuned. The EEC cuts back on the injectors for a spit second and counts how long it takes for the HEGO to report back a lean environment. EEC leans and enriches at different amounts and get back different numbers. These numbers tell EEC if the engine needs a tune up, or if performance parts have been added allowing the fuel amount delivered to be altered.
There is a Table called “Adaptive Fuel Table”. This table is used as a multiplier, it is held over the master load table. It then multiplies each number in the master table to get a better control of fuel delivery over time. In a computer that has been just connected to the battery it is full of “1’s”, if the master table is multiplied by 1 then it results in the same number, such as 14.7:1 X 1 = 14.7:1. After many days of driving on the highway the table begins to fill with multipliers like “1.2’s” and “0.9’s”, which will alter the master table. In example, 14.7:1 X 1.2 = 17.6:1, and 14.7:1 X 0.9 = 13.3:1, and thus the fuel curve has been fine tuned without doing anything special. While this may sound very simple, the downfall is that this entire technology depends on the Oxygen Sensors being fresh, clean, new, and in good condition. And it can’t be responsible for displacement changes, cam changes, or other big performance add-on’s. This technology is only meant to keep EEC on the same level as an aging engine with diminished performance. It is not meant to be relied upon for performance engine tuning!
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Article & images courtesy of fordfuelinjection.com.
