S H O R - Honda Civic Service Manual

Fuel and Emissions Systems
System Descriptions (cont'd)
ECM Data (cont'd)
w
Data
Description
Opera'ting Value Freeze Data
Fuel System
Status
Fuel system status is indicated as
"open" or "closed".
Closed: Based on the A,/F Sensor output, the ECM
determines the airlfuel ratio and controls the amount of
injected fuel.
Open: lgnoring Ay'F Sensor output, the ECM refers to
signals from the throttle position {TP), manifold absolute
pressure (MAP), intake air temperature (lAT), barometric
pressure (BARO), and engine coolant temperature (ECT))
sensors to control the amount of iniected fuel.
At idle speed: closed
YES
Short Term
F u e l T r i m
The airlfuel ratio correction coefficient for correcting the
amount of injected fuel when the fuel system status
is "closed." When the ratio is leaner than the
sloichiometric ratio, the ECM increases short term fuel
trim gradually, and the amount of iniected fuel increases.
The airlfuel ratio gradually gets richer, causing a lower
oxygen content in the exhaust gas. Consequently, the
short term fuel trim is lowered, and the ECM reduces the
amount of injected fuel.
This cvcle keeps the airlfuel ratio close to the
stoichiometric ratio when in closed loop status.
o . 7 1 . 5
Y E S
Long Term
F u e l T r i m
Long term fuel trim is computed from short term fuel trim
and indicates changes occurring in the fuel supply system
over a long period.
l f l o n g t e r m f u e l t r l m i s h i g h e r t h a n 1 . 0 0 , t h e a m o u n l o f
injected fuel must be increased. lf it is lower than 1.00, the
amount of injected fuel must be reduced.
0 . 8 1 . 2
Y E S
Intake Air
Temperature
{IAT)
The IAT sensor converts intake air temperature into
v o l t a g e a n d s i g n a l s t h e E C M . W h e n i n t a k e a i r
temperature is low, the internal resistance ofthe sensor
increases, and the voltage signal is higher.
W i t h c o l d e n g i n e :
S a m e a s a m b i e n t
t e m p e r a t u r e a n d E C T
YES
Throttle
Position
Based on the accelerator pedal position, the opening
anole of the throttle valve is indicated.
At idle speed:
a b o u t 1 0 %
YES
l g n i t i o n
T i m i n g
lgnition timing is the ignition advance angle set by the
ECM. The ECM matches ignition timing to driving
c o n d i t i o n s .
At idle speed: 8" t 5"
| ' t u L w n e n r n e > L )
s e r v i c e s i g n a l l i n e i s
jumped with the Honda
PGM Tester
NO
C a l c u l a t e d
L o a d V a l u e
(cLV)
cLV is the enoine load calculated from IMAP data.
At idle speed:
12 34%
At 2.500 rpm with no
t o a o :
't4- 34%
Y E S
11-14
\.,
r a