Air-fuel feed back control is the modulation which increases or decreases fuel injection quantity as determining exhaust gas rich or lean with HO2S adjust combustion is done at ideal air-fuel ratioto so as to raise the efficiency of catalytic convertor. Generally, NOx increases at lean combustion while CO, HC increases in rich combustion. Thus, in order to purge all of these gases with catalytic convertor, air-fuel ratio should be nearly at the ideal ratio. However the range in which all gases purified successfully is too narrow, it is impossible to meet ideal range with open loop control, therefore feed back control using HO2S is required. HO2S output signal changes rapidly near ideal air-fuel ratio and this characteristic is used at feed back control. comparing HO2S output signal and reference value, PCM increases fuel injection quantity at lean condition and decreases at rich condition. As deterioration of engine, due to the characteristic changes of many components of intake and fuel line or inevitable tolerance of components at production process, achieving ideal air-fuel ratio is almost impossible with the fixed fuel injection duration. Regarding the change of cross section by clogged injector, feed back correction is performed yet, it cannot cover all the ranges. It means if the correction range is massively seperated from the ideal value or if the mean of feed back control range too inclines to lean or rich condition, feed back correction does not work efficiently. Therefore processing correction value throughout long time statistically during driving, PCM controlls fuel injection duration as fitting the mean to be the ideal air-fuel ratio value. Through adaptive control, accuracy of the control could be improved and the value of adaptive control varies countiuously during driving and is always up-dated.

Checking air-fuel ratio correction value every 0.75 sec. at idle, if the value within the detecting condition for more than 0.3 sec., PCM sets P2190. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.

3.

Monitor sensors related to fuel trim(Ex. HO2S,MAFS,MAPS,TPS,MAPS,TPS,ECTS,PCSV,Injectors etc.) with scantool

4.

Are those parameters displayed correctly ?

▶ Fault is intermittent caused by poor contact in Sensor’s and/or PCM’s connector or was repairedand PCM memory was not cleared. Thoroughly check connectors for looseness, poorconnection, bending, corrosion, contamination, deterioration, or damage. Repair or replaceas necessary and go to "Verification of Vehicle Repair" procedure

▶ Go to "Terminal and connector inspection" procedure.

3.

Has a problem been found?

▶ Repair as necessary and go to "Verification of Vehicle Repair" procedure

▶ Go to "System Inspection " procedure.

1.

Check air clog.

(1)

Check Contamination ,Gasket installation as follows

▶ Damage or installation of throttle body gasket.

▶ Check clog of air cleaner

▶ Clog or contamination of intake manifold or injectors caused by foreign materials

▶ Check vaccum hose connected to surge tank is normal.

(2)

Has a problem been found ?

▶ Repair or replace as necessary and then, go to "Verification of Vehicle Repair"procedure.

▶ Go to "Check Fuel Pressure" as follows

2.

Check Fuel Pressure

(1)

Refer to "Fuel pressure test" in "Fuel delivery system"

(2)

Is the measured fuel pressure within specification ?

▶ Go to "Component Inspection" procedure.

▶ Repair or replace as necessary and the, go to "Verification of Vehicle Repair" procedure.

1.

Check PCV

(1)

IG "OFF".

(2)

Remove PCV valve and then, check that plunger in the PCV is moving.

(3)

Is the PCV normal ?

▶ Go to "Check PCSV" as follows.

▶ Substitute with a known-good PCV and check for proper operation. If the problem is corrected,replace PCV and then go to "Verification of Vehicle Repair" procedure.

2.

Check PCSV

(1)

IG "OFF".

(2)

Remove PCSV and Vaccum Hose

(3)

Check that PCSV is just one way solenoid valve

(4)

Is the PCSV normal ?

▶ Go to "Check injector" as follows.

▶ Substitute with a known-good PCSV and check for proper operation. If the problem is corrected,replace PCSV and then go to "Verification of Vehicle Repair" procedure.

3.

Check injector

(1)

IG "OFF"

(2)

Remove injector.

(3)

Check that injector hole is clogged by foreign materials.

(4)

Measure resistance between terminal 1 an 2 of injector connector.(Component Side)

Specification :

Temp.	Resistance
20℃ (68℉)	11.4 ~ 12.6Ω

(5)

Is the measured resistance within specification ?

▶ Go to "Check component related to fuel trim" as follows.

▶ Substitute with a known-good injector and check for proper operation. If the problem is corrected,replace injector and then go to "Verification of Vehicle Repair" procedure.

4.

Check component related to fuel trim

(1)

Check component related to fuel trim such as HO2S, MAFS,MAPS, TPS, ECTS, PCSV and Injectores) - Refer to each designated trouble shooting guide.

(2)

Are those component related to fuel trim O.K ?

▶ Substitute with a known-good PCM and check for proper operation. If the problem is corrected,replace PCM and then go to "Verification of Vehicle Repair" procedure.

note

There is a memory reset function on scantool that can erase optional parts automaticallydetected and memorized by PCM.

▶ Repair or replace as necessary and then, go to "Verification of Vehicle Repair" procedure.

After a repair, it is essential to verify that the fault has been corrected.

5.

Are any DTCs present ?

▶ Go to the applicable troubleshoooting procedure.

▶ System is performing to specification at this time.