Honda S2000 Service Manual page 240

Fuel and Emissions Systems
System Descriptions (cont'd)
ECM Data (cont'dl
Fuel system slatus is indicated as "open" or "closed".
Closed: Based on the HO2S output, the ECM determines
the airlfuel ratio and controls the amount of injected fuel.
Open: lgnoring HO2S 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
The air fuel ratio correction coefficient for correcting the
amount of injected fuel when the Fuel System Status is
"closed".
When the ratio is leaner than the stoichiometric
ratio, the ECM increase short term fuel trim gradually, and
the amount of injecled fuel increases. The air fuel 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 cycle keeps
the airlfuel ratio close to the stoichiometric ratio when in
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Long term fuel trim is computed from short term fuel trim
and indicates changes occuring in the fuel supply system
o v e r a l o n g p e r i o d .
l f l o n g t e r m f u e l t r i m i s h i g h e r t h a n 1 . 0 0 . t h e a m o u n t o f
injected fuel must be increased. lf it is Iower than 1.00. the
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The IAT sensor converts intake air temoerature into
voltage and signals the ECM. When intake air
temperature is low, the internal resistance of the sensor
a n d t h e v o l t a g e s i q n a l i s h i g h e r .
Based on the accelerator pedal position, the opening
e of the throtlle valve is indicated.
l g n i t i o n t i m i n g i s t h e i g n i t i o n a d v a n c e a n g l e s e t b y t h e
ECM. The ECM matches ignition timing to the driving
conditions.
CLV is the engine load calculated from the lvlAp data.
Short Term
F u e l T r i m
Calculated
Load Value
(CLV)
0 . 7 3 1 . 4 7 YES
YES
Long Term
F u e l T r i m
I n t a k e A i r
Temperature
{IAT)
l g n i t i o n
T i m i n g
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
At idle speed:
5'+ 5" BTDC with the
S C S s e r v i c e s i g n a l l i n e
jumped with the Honda
P G M
At idle speed:
22 42%
At 2,500 rpm with no
load:
21 48yo
11-12