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Dodge Caliber. Manual - part 1145
OPERATION
Short Term
The first fuel correction program that begins functioning is the short term fuel correction. This system corrects fuel
delivery in direct proportion to the readings from the Upstream O2 Sensor.
The PCM monitors the air/fuel ratio by using the input voltage from the O2 Sensor. When the voltage reaches its
preset high or low limit, the PCM begins to add or remove fuel until the sensor reaches its switch point. The short
term corrections then begin.
The PCM makes a series of quick changes in the injector pulse-width until the O2 Sensor reaches its opposite
preset limit or switch point. The process then repeats itself in the opposite direction.
Short term fuel correction will keep increasing or decreasing injector pulse-width based upon the upstream O2 Sen-
sor input. The maximum range of authority for short term memory is 25% (+/-) of base pulse-width. Short term is
violated and is lost when ignition is turned OFF.
Long Term
The second fuel correction program is the long term adaptive memory. In order to maintain correct emission
throughout all operating ranges of the engine, a cell structure based on engine rpm and load (MAP) is used.
Ther number of cells varies upon the driving conditions. Two cells are used only during idle, based upon TPS and
Park/Neutral switch inputs. There may be two other cells used for deceleration, based on TPS, engine rpm, and
vehicle speed. The other twelve cells represent a manifold pressure and an rpm range. Six of the cells are high rpm
and the other six are low rpm. Each of these cells has a specific MAP voltage range Typical Adaptive Memory Fuel
Cells .
As the engine enters one of these cells the PCM looks at the amount of short term correction being used. Because
the goal is to keep short term at 0 (O2 Sensor switching at 0.5 volt), long term will update in the same direction as
short term correction was moving to bring the short term back to 0. Once short term is back at 0, this long term
correction factor is stored in memory.
The values stored in long term adaptive memory are used for all operating conditions, including open loop and cold
starting. However, the updating of the long term memory occurs after the engine has exceeded approximately 170°-
190° F (77° to 88°C), with fuel control in closed loop and two minutes of engine run time. This is done to prevent
any transitional temperature or start-up compensations from corrupting long term fuel correction.
Long term adaptive memory can change the pulse-width by as much as 25%, which means it can correct for all of
short term. It is possible to have a problem that would drive long term to 25% and short term to another 25% for a
total change of 50% away from base pulse-width calculation.
Typical Adaptive Memory Fuel Cells
Open
Throttle
Open
Throttle
Open
Throttle
Open
Throttle
Open
Throttle
Open
Throttle
Idle
Decel
Vacuum
20
17
13
9
5
0
Above 1,984
rpm
1
3
5
7
9
11
13 Drive
15
Below 1,984
rpm
0
2
4
6
8
10
12
Neutral
14
MAP volt =
0
1.4
2.0
2.6
3.3
3.9
Fuel Correction Diagnostics
There are two fuel correction diagnostic routines:
•
Fuel System Rich
•
Fuel System Lean
A DTC is set and the MIL is illuminated if the PCM detects either of these conditions. This is determined based on
total fuel correction, short term times long term.
PM
FUEL INJECTION
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