Ford Tuning: Load with failed MAF table(s)

Introduction / Prerequisites

Before you read this, make sure you have read Theory: Alpha-N, Theory: Mass Air Flow and the FordOverview.  Although not essential, it wouldn’t hurt to have at least read about Speed-Density operation as well.  This page will assume you have read and understood these pages.  This is a somewhat complicated topic and will require you to put several pieces together so don’t feel bad if you have to read this a couple times.

About the table and why it is critical

The “Load with failed MAF” (“LWFM” from here forward) table(s) are found in almost all MAF Ford Strategies.  Most strategies that make use of IMRCs (Intake Manifold Runner Control – valves that restrict air entering the engine in order to increase tumble and velocity) have two LWFM tables instead of one and  switch from one LWFM table to the other as the IMRCs open and close.  The main purpose of the LWFM table is to estimate the amount of air going into the engine without using the MAF sensor or a MAP sensor (if present) to provide the ECM with an “emergency” fallback method of running the engine in the event the MAF sensor fails.

The LWFM table is also important for normal operation of the motor because Load from the MAF (this is “Load” – the Ford-specific calculated cylinder filling value calculated from the MAF sensor, RPM and engine displacement) is “sanity checked” against the LWFM table to determine if the MAF is providing reliable information.  If there is too large of a difference between calculated Load and the LWFM table, the ECM may ignore the MAF even if it is providing valid information! This happens most commonly in forced induction situations (where load is greatly increased compared to a naturally aspirated car) but can also occur in cars with aggressive camshafts.  If you are making changes to a MAF transfer function and you are not seeing any changes in engine operation, double check your LWFM table!  Further, most strategies use “Anticipation logic” to predict airflow.  This prediction logic is based off…  Surprise… The LWFM table!  Having a sane LWFM table is neccesary for the aircharge anticipation logic to work.  You can disable this but it’s generally not necessary if you tune the LWFM table properly.

LWFM table is a classic example of an Alpha-N control strategy – it’s purpose is to provide a very crude estimation of airflow entering the engine when the MAF signal is absent or the ECM thinks it is unreliable.   The LWFM table uses only two inputs – throttle position (aka “TP”) and RPM to determine Load.  Here is a picture of a typical LWFM table: (screenshot from Binary Editor / GUFB strategy)

Here you can see the X axis is RPM and the Y axis is RELATIVE Throttle Position volts.  Each cell represents the Load that will be used to calculate fueling and timing when the ECM thinks the MAF is bad.  For example, idling with the throttle closed (0 volts relative)  around 700 RPM the ECM will assume a Load of .1602 and make appropriate fueling and timing changes.

The importance of the LWFM table varies considerably from strategy to strategy.  A rule of thumb is that the newer of an ECM you are using the more picky it will be able the LWFM table.  Fox Body and most early EECV (pre-99) are fairly tolerant of inappropriate LWFM tables where 99+ ECMs are generally much, much, much more picky.

Tuning the LWFM Table

Tuning the LWFM table is pretty simple:

First, set the Aircharge WOT multiplier, Anticipation logic scalars, etc. to make the ECM as tolerant of a bad failed MAF table as possible

Second, GUESS!   Yes, guess.  Enter values that you think are sane for the setup, starting with the stock LWFM table as a guideline.  A few examples:

  • If you put in aggressive cams, decrease the LWFM table at low RPMs and throttle angles while increasing it at higher RPMs and throttle angles.
  • If adding a positive displacement supercharger (roots, twin screw) multiply the whole LWFM table by approximately the highest pressure ratio you will see.
  • If you add a centrifugal blower, multiply a column of the LWFM table by the pressure ratio you achieve at a given RPM

Third, drive around and log throttle position (TP Relative), RPM, Load.  Compare the Load values you log with the LWFM table.  Start changing entries in the table so they get closer to the load you really see at given TP and RPM conditions.

Note: Turbo cars present a very big challenge to this strategy due to the amount load can vary with throttle position due to spool time.  This is a very tricky case and often the only solution is to try and maximize allowed error before the LWFM table becomes active and also disable Aircharge Anticipation and other functions dependent on the LWFM table.