86GT
11-01-2005, 09:21 PM
Here is how the GUFB book states:
Transient Fuel is variously referred to as manifold wall wetting, puddling, filling, fuel film condensation/evaporation.
A liquid fuel film resides on the walls of the intake manifold. The film mass varies primarily with manifold absolute pressure and manifold wall temperature. During steady state conditions, the film mass is constant. The rates of condensation and evaporation on the manifold walls are equal.
During transients, the film mass changes creating air/fuel ratio errors. During accelerations, the film mass increases. Fuel will condense faster on the manifold walls until equilibrium is reached. In an uncompensated system at stoichiometry, fuel is diverted from the cylinders, resulting in a momentary lean condition.
During decelerations, the film mass decreases. Fuel will evaporate faster from the manifold walls until equilibrium is reached. In an uncompensated system at stoichiometry, fuel is added to the cylinders, resulting in a momentary rich condition.
The problem is magnified in closed loop fuel systems because the fuel control will incorrectly chase the transient air/fuel excursions.
INTENT
The Transient Fuel Compensation Strategy (TFC) augments the closed/open loop fuel control to keep cylinder events at the desired air/fuel ratio during all engine transients. The goals are:
To eliminate lean air/fuel excursions during accelerations.
To eliminate rich air/fuel excursions during decelerations.
I personally have found the MEFTRA scalar more valuable so far. This is the Equilibrium Accel multiplier. It allows for riching the mixture during accel.
The MEFTRD scalar is the Deccel Equilibrium multiplier. This one helps in the decel popping which is caused by to much fuel in the decel.
I am starting to play with the Equilibrium table to fine tune the Accel at certain loads. Larger numbers I believe are to richen the mixture. You just have to keep in mind that by raising the number you will richen the mixture on accel and lean the mixture on decel. I am still playing with the table to prove what I am seeing.
Another key point for those of you that have modified the Load scale (normalizers FN071), this will affect the Equilibrium tables and throw it way out of whack.
When I changed my load scale (FN071) the car ran completley different during non steady throttle states. I then went to the Equilibrium table and moved the numbers around to mimic the factory table and the car drove much better. So for those of you that do not have access the the Equilibrium tables, I would not recommend changing function 071.
Transient Fuel is variously referred to as manifold wall wetting, puddling, filling, fuel film condensation/evaporation.
A liquid fuel film resides on the walls of the intake manifold. The film mass varies primarily with manifold absolute pressure and manifold wall temperature. During steady state conditions, the film mass is constant. The rates of condensation and evaporation on the manifold walls are equal.
During transients, the film mass changes creating air/fuel ratio errors. During accelerations, the film mass increases. Fuel will condense faster on the manifold walls until equilibrium is reached. In an uncompensated system at stoichiometry, fuel is diverted from the cylinders, resulting in a momentary lean condition.
During decelerations, the film mass decreases. Fuel will evaporate faster from the manifold walls until equilibrium is reached. In an uncompensated system at stoichiometry, fuel is added to the cylinders, resulting in a momentary rich condition.
The problem is magnified in closed loop fuel systems because the fuel control will incorrectly chase the transient air/fuel excursions.
INTENT
The Transient Fuel Compensation Strategy (TFC) augments the closed/open loop fuel control to keep cylinder events at the desired air/fuel ratio during all engine transients. The goals are:
To eliminate lean air/fuel excursions during accelerations.
To eliminate rich air/fuel excursions during decelerations.
I personally have found the MEFTRA scalar more valuable so far. This is the Equilibrium Accel multiplier. It allows for riching the mixture during accel.
The MEFTRD scalar is the Deccel Equilibrium multiplier. This one helps in the decel popping which is caused by to much fuel in the decel.
I am starting to play with the Equilibrium table to fine tune the Accel at certain loads. Larger numbers I believe are to richen the mixture. You just have to keep in mind that by raising the number you will richen the mixture on accel and lean the mixture on decel. I am still playing with the table to prove what I am seeing.
Another key point for those of you that have modified the Load scale (normalizers FN071), this will affect the Equilibrium tables and throw it way out of whack.
When I changed my load scale (FN071) the car ran completley different during non steady throttle states. I then went to the Equilibrium table and moved the numbers around to mimic the factory table and the car drove much better. So for those of you that do not have access the the Equilibrium tables, I would not recommend changing function 071.