What were you thinking? That is one question asked a lot, usually after something goes wrong. Lets ask EEC what she was thinking now, before something goes wrong. EEC thinks in a “flow-log,” but humans looking at a flow-log / data table without a degree makes us stare off into space and drool a lot. So it has to be converted into text and broken up into what? Yep strategies! A strategy is the arranging and planning of actions with reference to accomplishing a short-range objective. So we come up with several different strategies and we can accomplish a long-term goal. This is good information for diagnosing and setting up a good Ford EEC EFI system. If we know what the computer is thinking, we can understand why certain things happen, and why certain things don’t. There is about 50-200KB of raw data inside the computer that we can break down into 0000000 different strategies. Try to combine the strategies together after you read it once or twice.
Please don’t write us “My Grandma’s 1990 Taurus SHO does this instead, are you stupid,” e-mails just yet. Not all EEC’s are programmed the same, the following is typical logic for typical engines. Some actual numbers and dividing lines could be different for some models. Now lets start strategizing.
Start / Crank
This is the start (I know, bad joke). 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
These tell the EEC that you have just checked the dash, want the engine to start, and have turned the key. Even though you’ve heard the fuel pumps whirr, the injectors haven’t released any fuel until it senses engine rotation. Even when the engine does turn over 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 it dumps 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 you hold the key in the start position. What if things go bad, your ignition system could not light the engine, and it become flooded? Press the accelerator to the floor while starting, the full open TPS reading will tell the EEC to cut the injectors back to almost nothing. When you decide the fuel has been flushed out release the pedal and the EEC will fire the injectors and the engine fires up. 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 we have to get adjusted. Well EEC does anyway, this strategy is kind of like you waking up with a hangover next to a stranger. Where’d I set my pants, should I run fast, should I sneak quietly! EEC’s first reaction is to keep the throttle air bypass open 100% or else we’ll be back to engine crank mode. RPM will drop however, usually to around 1000RPM after a few seconds, then drop down to base idle as she gets warmer (about 160°F). 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 she gets warmer (about 170°F) she will lean out the mixture. This logic will speed up the time it takes to heat up the engine and converter. Now lets talk about what happens when last nights date wakes up (driver input). If you drive away with ECT under 185°F she jumps to cold drive-away strategy. If you stay asleep and leave everything alone ECT will cross 185°F in about 4 minutes and we are now in a warm idle. See how confusing it all gets at this point.
BUT don’t be hesitant about driving your car at any time; they wouldn’t make all the strategies if you couldn’t use them. The Government wants you to drive your car as soon as you start it for economy purposes; cold cars burn more fuel so let’s get them warmer quicker! Now hold on, I recommend a few seconds to ensure oil pressure, and let’s hold up on the wide-open throttle assault until we have some nice warm oil for all the internals. Lets all practice common sense and a little love for our vehicles.
So the TPS and PIP are going up, the MAF/MAP is showing greater load, and the ECT is under 185°F. The TPS and MAF/MAP tell EEC that we are 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. We have 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 us into normal operating temperatures quicker. Timing is advanced and retards slowly as temps rise. Once the ECT temp cross’s 185°F the mixture should return to normal and relate to HEGO signal as long as you aren’t accelerating 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 us down the road from here.
This one tends to be more about emissions. Warm idle occurs if the engine starts and ECT rises above 185°F, we come up to a stoplight, or place it back into neutral. The computers is programmed with a target RPM for idle, typically it’s around 672RPM. Typically the computer is struggling to achieve its target RPM. 255°F is the magic number to start complaining about overheating. Let’s break it down by system. Fuel is now closed loop with HEGO switching. We are now aiming for 14.7:1 A/F ratio for perfect emissions, enrichment will occur only if the ECT is above 225°F. There will be no EGR operation at these RPM’s. Timing is mildly advanced and will begin to retard after a minute. We need hot exhaust gasses 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, we need a nice smooth idle. Not to high with A/T transmissions to prevent creep at stoplights. Idle will increases 100-200RPM if the ECT or ACT is over 225°F. 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.
We have come to a point where we are happy with our speed and want to just cruise into the sunset. What sounds easy turns out to be one of the most in-depth strategies we use. It is assumed that we citizens spend most of our time at cruise (yeah right), so we need the lowest emissions, 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. We still have the throttle air bypass 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%; this means we don’t need 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, we need extra airflow 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.
Seat belts on please, this is the master plan, what is the quickest route from point A to point B? Wide-Open throttle assaults of course. 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 rear wheels. Fuel enriches to a preset level even further the colder the ACT is. The timing jumps up to a maximum preset level around 28°BTDC, 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 until we reach that edge. If you buy a new car and add timing with a chip or by twisting the dizzy you could cause detonation. People do this to get more timing and better performance. So the Knock sensor is there to stop the owner that twists the dizzy for more performance from blowing a ring or burning some valves. The throttle air bypass remains at 100% giving you a larger throttle inlet and as a back up incase 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. We also need a rev limiter and speed limiter for the safety of the vehicle; 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.
The vehicle is moving and you lift your foot off the accelerator. EEC sense’s the TPS go to closed and VSS signal slow. This presents a few problems that are easily overcome. First we have to prevent stalling; 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 we reach a stop and move back into warm idle strategy. We are always thinking of emissions and burning fuel as we decelerate is a big waste. EEC turns the injectors completely off when RPM is over 1500 and the engine is over 140°F. Injectors begin operating under 1500RPM or if you hit the skinny pedal. If you don’t run a VSS you can run the risk of stalling when slowing down from over 1500RPM. 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 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. Hold on that sounds hard! Not really, randomly 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; EEC replaces the sensor reading with a best guess from a past memory. This is why unplugging the battery to fix something works against you. Unplug 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.
I am going to divide up the sensors 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.
Now this one is a little complex. EEC likes to toy with the fuel ratio at random. It does this to run complex math equations. She is calculating how much fuel is required to reach certain lean or rich states. Why you ask? Because playing this cat and mouse game with the fuel ratio allows us to fine tune the engine parameters in other strategies. Confused yet? 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 you’ve added a performance parts and allows us to actually alter the fuel amount delivered. What do we do with those numbers EEC collected? Well there is a Table called “Adaptive Fuel Table” (makes sense huh?) 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 you multiply the master table by “1″ you get the same number. I’m not good at math
and I understand it, 14.7:1 X 1 = 14.7:1, simple!. After many days of driving on the highway it begins to fill with multipliers like “1.2′s” and “0.9′s”, which will alter the master table. Don’t believe me? 14.7:1 X 1.2 = 17.6:1, and 14.7:1 X 0.9 = 13.3:1, and we just fine tuned our fuel curve without doing anything special. Isn’t that cool? Well not always, 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 ageing engine with diminished performance. It is not meant to be relied upon for performance engine tuning!