TECHNICAL NOTES ON THE EEC-IV MCU - Auto diagnostics

Eectch98-Part3.fm
would be equivalent to raising the nitrogen content of air from 78 or 79% up to
around 82 or 85%. The more dilute oxygen tends to lower the combustion chamber temperature.
The reverse is true when you shoot nitrous oxide into an engine. In that
case, you raise the oxygen content of the air and, consequently, raise the combustion
pressures and temperatures (and not incidentally, power).
ACT
This is snagged from the graph in the Calibrator demo program. To determine air
temp you can measure voltage at the ACT (air charge temp sensor). Reference is 5.0
volts.
Air Temp o F 50 68 86 104 122 140 158 176 194 212 230 248
Voltage 3.52 3.06 2.62 2.16 1.72 1.35 1.04 .80 .61 .47 .36 .28
Normally, the distributor
contains the TFI (Thick
Film Ignition) module and a
hall effect pickup with a
vane stator. The PIP (Profile
Ignition Pickup)
Signal begins when the
hall-effect timing pickup
switch sends a signal to
the TFI module. Modification
by a schmitt trigger
converts this signal to a
logic compatible output
that is then sent to the
EEC, which is responsible
for
Table 52: ACT Transfer Function
TFI / PIP
Early EEC’s used a sectored
wheel (vanes) in the
distributor with the number
of vanes being equal to
half the number of cylinders.
Later EECs utilize a
36 tooth wheel, with a
missing tooth for synchronization, whose output is pre-processed by a unit known as
the EDIS (Electronic DIStributor). The EEC processes the PIP signal and subsequently
feeds a properly advanced or retarded signal back to the TFI ignition module
to fire the plug.
EEC-IV Technical Notes: Sensors 47 last edited: 9/29/98