Inspection Procedure 18

Inspection procedure 18: Too high CO and HC concentration when idling

COMMENT

- Abnormal air/fuel ratio is suspected.

TROUBLESHOOTING HINTS (The most likely causes for this case:)

- Fuel pump system failed.

- Heated oxygen sensor failed.

- Ignition system failed.

- Poor compression.

- Improper operation of the PCV valve.

- Evaporative emission control system failed.

- ECM failed.

DIAGNOSIS

Required Special Tool:

- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.

- MB991827: USB Cable

- MB991910: Main Harness A

STEP 1. Using scan tool MB991958, read the diagnostic trouble code (DTC).





CAUTION:
To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK"
(OFF) position before connecting or disconnecting scan tool MB991958.

(1)Connect scan tool MB991958 to the data link connector.
(2)Turn the ignition switch to the "ON" position.
(3)Read the DTC.
(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is any DTC set?

YES Refer to, Diagnostic Trouble Code Chart Multiport Fuel Injection (MFI).

NO Go to Step 2.

STEP 2. Check the ignition timing.

Testing and Inspection.

Q. Is the ignition timing normal?

YES Go to Step 3.
NO Check for installed conditions of the timing chain. Then confirm that the malfunction symptom is eliminated.
STEP 3. Using scan tool MB991958, check data list.

(1)Turn the ignition switch to the "ON" position

(2)Check the following items in the data list. Refer to Data List Reference Table Data List Reference Table.
1. Item 5: Intake Air Temperature Sensor

2. Item 6: Engine Coolant Temperature Sensor

3. Item AC: Heated Oxygen Sensor (front)

4. Item AD: Heated Oxygen Sensor (rear)

(3)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Are they operating properly?

YES Go to Step 4.
NO Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 4. Check the fuel pressure.

Refer to, Fuel Pressure Test Testing and Inspection.

Q. Is the fuel pressure normal?

YES Go to Step 5.
NO Repair it. Then confirm that the malfunction symptom is eliminated.
STEP 5. Check the spark plugs.

Procedures.

Q. Are there any abnormalities?

YES Replace the spark plug. Then confirm that the malfunction symptom is eliminated.
NO Go to Step 6.
STEP 6. Check the ignition coil.

Testing and Inspection.

Q. Are there any abnormalities?

YES Replace the ignition coil. Then confirm that the malfunction symptom is eliminated.
NO Go to Step 7.
STEP 7. Check the compression pressure.

Testing and Inspection.

Q. Is the compression pressure normal?

YES Go to Step 8.
NO Repair it. Then confirm that the malfunction symptom is eliminated.
STEP 8. Check the positive crankcase ventilation system.

Crankcase Ventilation System Check.

Q. Is the positive crankcase ventilation system normal?

YES Go to Step 9.
NO Repair it. Then confirm that the malfunction symptom is eliminated.
STEP 9. Check the evaporative emission control system.

Purge Control System Check.

Q. Is the evaporative emission control system normal?

YES
Check the following item, and repair or replace the defective item.
5. Check if the injectors are clogged.
Then
confirm that the malfunction symptom is eliminated.

NO Repair it. Then confirm that the malfunction symptom is eliminated.