Precision Turbo and Engine BigStuff3 GEN3 PRO SEFI System Hardware & BigComm Software - Manual (Page 94)

BigStuff3 Pro SEFI System
Version 2.1 – February 2011 87
where the acceleration event occurred (AE Position Correction). Below, is a description of how the
TPS Transient Fuel requirements are calibrated using the dTPSdt and AE Position Correction tables.
55. Accel Pump Shot
The first TPS Transient Fuel control table is Accel Pump Shot and as the name insinuates it can be
compared to a carburetor’s accelerator pump shot. The ECU uses the Accel Pump Shot table value to
compute the size of the Asynchronous Pulse Width (APW) for a given rate of throttle change. It does
so by sensing the rate of the throttle change and then using the corresponding Accel Pump Shot table
value to calculate the size of the asynchronous pulse width. For example, if the ECU detected a
throttle change of 10 degrees / second (dTPSdt), it would immediately look up the corresponding
Accel Pump Shot table value of let’s say 2ms. After the asynchronous pulse is looked up, the ECU
then uses AE Position Correction table (see below) to modify the asynchronous pulse size relative to
the throttle position at which the dTPSdt event occurred. If the Accel Pump Shot pulse width is less
than the injector opening time, the fuel will not be delivered asynchronously. Instead, it will be
accumulated and added to the next synchronous pulse width.
Note: The value in the first cell (the cell all the way to the left) must always be zero (0).
Working from left to right, each input cell in the Accel Pump Shot table represents a 1% change in
throttle angle for a total percent change of 15%. This is plenty of resolution since the ECU looks for
changes every 20 milliseconds. As a reference point, it typically takes approximately 250 milliseconds
for a person to slam the throttle open.
While the engine is running, a “real-time Ellipse” will move within the Accel Pump Shot table
relative to the current Accel Pump Shot “operating point”. Use it as a point of reference to help
calibrate the Accel Pump Shot table.
To change a value in the Accel Pump Shot table, move the cursor using the PC’s mouse or arrow keys
to the cell to be changed. Input the desired value and hit
“Enter”
to save the change. The values
need to be larger as you work from the left to right. The greater the throttle angle rate of change, the
larger the Accel Pump Shot table value needs to be.
56. AE Position Correction
The second TPS transient fuel control table is AE Position Correction. It can be compared to a
carburetor’s accelerator pump “cam” profile. The ECU uses the AE Position Correction table value to
modify the size of the Asynchronous Pulse Width (APW) relative to the throttle position at which the
dTPSdt event occurred. For example, if a 10
o
/second dTPSdt event occurred (resulting in a look up of