Adaptive Fuel Control Strategy

The fuel control system uses the adaptive fuel table to compensate for normal variability of the fuel system components caused by wear or aging. During closed-loop vehicle operation, if the fuel system appears "biased" lean or rich, the adaptive fuel table will shift the fuel delivery calculations to remove the bias. The fuel system monitor has two means of adapting Short Term Fuel Trim (SHRTFT) and Long Term Fuel Trim (LONGFT). SHRTFT is referred to as LAMBSE and LONGFT reference the adaptive fuel table.

Short Term Fuel Trim (SHRTFT) (displayed as SHRTFT1 and SHRTFT2 on the NGS tool) is a parameter that indicates short-term fuel adjustments. SHRTFT is commonly referred to as LAMBSE. LAMBSE is calculated by the PCM from HO2S inputs and helps maintain a 14.7:1 air/fuel ratio during closed-loop operation. This range is displayed in percentage (%). A negative percentage means that the HO2S is indicating RICH and the PCM is attempting to lean the mixture. Ideally, SHRTFT should remain near 0% but has the ability to adjust between -25% to +35%.

Long Term Fuel Trim (LONGFT) (displayed as LONGFT1 and LONGFT2 on the NGS tool) is the other parameter that indicates long-term fuel adjustments. LONGFT is also referred to as Adaptive Fuel. LONGFT is calculated by the PCM using information from the SHRTFT to maintain a 14.7:1 air/fuel ratio during closed-loop operation. The Adaptive Fuel strategy is expressed in percentages. The range of authority for LONGFT is from -35% to +35%. The ideal value is near 0% but variations of ±20% are acceptable. Information gathered at different speed load points are stored in adaptive fuel cells in the adaptive fuel tables, which can be used in the fuel calculation.

SHRTFT and LONGFT work together. If the HO2S indicates the engine is running rich the PCM will correct the rich condition by moving SHRTFT in the negative range (less fuel to correct for a rich combustion). If after a certain amount of time SHRTFT is still compensating for a rich condition, the PCM "LEARNS" this and moves LONGFT into the negative range to compensate and allows SHRTFT to return to a value near 0%.

As the fuel control and air metering components age and vary from nominal values, the adaptive fuel strategy learns corrections while in closed-loop fuel control. The corrections are stored in a table that is a function of engine speed and load. The tables reside in Keep Alive Memory (KAM) and are used to correct fuel delivery during open and closed-loop. As changing conditions continue the individual cells are allowed to update for that speed load point. If, during the adaptive process, both SHRTFT and LONGFT reach their high or low limit and can no longer compensate, the MIL is luminated and a DTC is stored.

Whenever an injector or fuel pressure regulator is replaced, KAM should be cleared. This is necessary so the fuel strategy does not use the previously learned adaptive values.

Lambse is the A/F ratio that the EEC is commanding or you could call it targeted or short term fuel trim. In a perfect world the Lambse is the A/F ratio that you should see on a wideband.
 

The value of lambse is calculated from the various fuel tables.


In closed loop operation Lambse is the calculated A/F ratio needed to maintain the set point (14.64:1) as reported by the O2's, and it seems to adjust much faster then KAMREF correction value. In open loop LAMBSE is the a/f ratio that the computer believes is being injected.
Lambda is A/F ratio expressed as a percentage of 14.7:1. Just divide the A/F ratio by 14.7 to get lambda, or multiply lambda by 14.7 to get an A/F ratio. If the lambda is .88, the A/F ratio is 0.88 * 14.7 = 12.936
It's just a percentage of stoich, or 14.7:1 A/F ratio. To convert a lambda value to an A/F ratio just multiply by 14.64. exmp: 1.25 lambda * 14.64 = 18.3 A/F ratio

Reputable Tuner Notes:

KAMREF is a multiplier of the Air Mass or the learned correction factor or long term fuel trim, if you clear the KAM and turn off adaptive then it will stay 1. For the A9L it is used as:


0.5 * AM * KAMRF1
---------------------- = BASEFF1
14.64 * LAMBSE1


So any value above 1 is adding fuel and less than 1 is leaning.
Generally I tune up to about 4k rpm by getting in 2nd/3rd and holding at an rpm and logging. I make my adjustments based on KAMRF1, kg/hr etc and then go up 500 rpm and do it over again. Once I start getting into WOT things are a bit more complicated and that is where the WB really shines.

- Mike Glover, STKR

If your adaptive is disabled at WOT your KAMRF will not show anything but 1.00 anytime it is in OL.
Because you are never in closed loop mode at WOT and heavy load values, the EEC does not have many valid data points (via feedback from the O2's) at those RPM/Load values to work with. So it does the best it can. I believe it probably learns a general assumption about your MAF curve and extrapolates any corrections the best it can up the curve. But I would say that it probably does not adjust as much at WOT as it will at idle, part throttle, etc.

EEC-IV ADAPTIVE CONTROL
YOUR BEST FRIEND OR YOUR WORST NIGHTMARE!
By: Mike Wesley

Welcome to the wonderful world of EEC electronics! (pronounced "EEK") This is the first in a series of articles here on The Mustang Works dealing with the EEC. We will be discussing various aspects of the EEC in a Mustang. By understanding how the EEC controls the engine, hopefully you'll get a better idea of why some changes to your engine may or may not perform as you expected. Through a series of articles, we will go through major sections of the EEC and how they work with common aftermarket parts. Some of this might be old news to a few, but alot of it goes way beyond what has ever been written before. In each issue we will go through sections like: Adaptive Control, MAFs and Injectors, Closed Throttle / Part Throttle / Wide Open Throttle, Sensors and what they do, Replace the EEC or Re-Calibrate, Fooling the EEC, Fuel Control, Spark Control, Speed Density Vs. Mass Air, Power Adders and the EEC, and EEC Transmission Control.

I'm sure you've all heard something about the EEC's Adaptive Control system, but what exactly is it, and what does it do? Before we get into the Adaptive Control system, let's define a few common terms:

The Adaptive Control system is used to correct changes in engine operation caused by variations in air metering and fuel delivery devices. The Adaptive Control system corrects the problems of variability by making changes to fuel flow based on what it has 'learned' about the system. If your engine is running leaner than it should, the Adaptive Control system can richen the system up automatically. The same thing if it is running a bit rich. The EEC has a special block of memory called the Keep Alive Memory where it stores information about how the engine is operating. By looking at the oxygen sensors, the EEC can tell if the amount of fuel it is delivering is the same amount actually going into the cylinders at a given Speed / Load point. In the Keep Alive Memory, there is a table that represents Speed / Load points normally used during Closed Loop control. As the EEC reads the oxygen sensors, it updates this table if it finds any differences in the fuel delivered and the A/F ratio measured. As an example, we will look at how the Adaptive Control system works if fuel pressure is something other than stock.

From this example, you'll quickly see why an adjustable pressure regulator might not be a good investment of your money. Ford uses a fuel pressure of roughly 39 PSI to rate it's fuel injectors. The fuel regulator operates in conjunction with manifold pressure to keep the delta pressure across the fuel injectors at roughly 39 PSI at all times. In the EEC calibration, there is a number that represents the size of the injectors installed in the engine. This number represents how much fuel the injector will flow at 39 PSI. The EEC uses this number, along with airflow information to correctly calculate A/F ratio. Based on the airflow number and it's target A/F ratio, the EEC pulses the fuel injector to give just the right amount of fuel to reach it's target A/F ratio at any given Speed/Load point. Now if you were to increase the fuel pressure, the amount of fuel delivered for a given pulsewidth would go up since more fuel will be forced through the injector. As soon as the EEC goes into Closed Loop control, it will 'see' this increased fuel pressure. The reason for this is for any given pulsewidth, the A/F ratio as measured by the oxygen sensor will be richer than what the EEC wanted it to be since now there is more fuel delivered with the same pulsewidth. The EEC will calculate the difference from what it wanted and what it got and update the Adaptive table with a 'correction factor' and use this correction factor to reduce the injector pulsewidth the next time the injector fires. Eventually what happens is the EEC is able to 'dial out' the extra fuel that was added by increasing the fuel pressure. Now you can probably see why raising the fuel pressure is only a temporary 'fix' for a lean problem. Soon you will be right back where you started from. The EEC is continuously updating the Adaptive table anytime it is in Closed Loop.

"What about Open Loop?" you might ask. Well, it works there too. This fact alone is know by very few people. Most people think Adaptive only works when in Closed Loop. This is wrong! Adaptive is only UPDATED during Closed Loop. It would be silly to ignore changes in the air and fuel system in Open Loop and only correct them in Closed Loop. If you have a serious fuel problem, your car might not even start if the EEC didn't have some way of correcting things all the time. The way the EEC uses Adaptive in Open Loop is similar to Closed Loop except it doesn't update the table. This means it's not looking at the oxygen sensor for feedback. It is merely relying on the information stored in the table to make corrections. Since the Adaptive table only contains Speed / Load points normally seen during Closed Loop, where does the correction factor come from if I'm at WOT? Good question. The answer is; it uses the last value it was using while in Closed Loop. Since the Keep Alive Memory has power to it even when the ignition key is turned off, the Adaptive table retains it's information. The only way to clear the Adaptive table is by disconnecting the vehicle's battery. Do that and you're back to working with a clean slate and the whole process starts over again. Now there are limits to how much the Adaptive Control system can change the calibrations. The adaptive system has a range of roughly +/- 25%. If you had an adjustable fuel pressure regulator installed, and you needed more fuel, you could keep cranking it up until the EEC could no longer dial the fuel back out. The problem with this is you will set a code and the 'Check Engine' light might come on.

A quick tip. When setting your fuel pressure, always check it with the vacuum reference DISCONNECTED! The pressure reading with the vacuum connected to the regulator depends on how much vacuum your engine pulls at idle. Depending on your camshaft, this can vary quite a bit. If you have a big cam and set your idle pressure to 32 PSI with the vacuum reference connected, you might only be getting 36 PSI at WOT. It's VERY important to set the idle pressure with the vacuum reference disconnected. This way you know for sure how much fuel pressure you get at WOT.

14.7 is ideal if you want to completely use up all of the fuel AND all the oxygen sent into the combustion chambers. Something a bit leaner, like 15.5 to 16.2 or so, is more ideal for best cruise fuel mileage. But running this mixture level for extended periods is hard on cat cons &/or produces excess nitrogen oxides iirc.

The numbers typically batted around for engines that don't typically need extra fuel to inhibit knock are:

6.0:1 Rich run limit
9.0:1 Low power, black smoke
11.5:1 Rich best torque
12.5:1 Safe best power
13.2:1 Lean best torque
14.7:1 Chemically ideal
15.5:1 Lean light load, part throttle
16.2:1 Best economy, part throttle
18:1 Lean run limit

These numbers go out the window if you are running boost, typically need to go a full point richer or more than 12.5:1 to ensure complete safety vs knock.

Chris Slaw