Inspection Procedure 15

INSPECTION PROCEDURE 15: Hesitation, sag or stumble.

COMMENT
- In cases such as the above, the ignition system, air/fuel mixture or compression pressure may be defective.

TROUBLESHOOTING HINTS (The most likely causes for this case)
- Malfunction of the ignition system.
- Malfunction of air/fuel ratio control system.
- Malfunction of the fuel supply system.
- Malfunction of the EGR system.
- Poor compression pressure.

DIAGNOSIS

Required Special Tools:
- 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 the DTC set?

YES: Refer to Diagnostic Trouble Code Chart. Diagnostic Trouble Code Descriptions

NO: Go to Step 2.

STEP 2. Using scan tool MB991958, check actuator test items 1, 2, 3, 4: Injector.




1. Check following items in the actuator test. Refer to Actuator Test Reference Table. Actuator Test Reference Table
a. Item 1, 2, 3, 4: Injector.

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

Q: Are they operating properly?

YES: Go to Step 3.

NO: Refer to DTC P0201 - Injector Circuit-cylinder 1, DTC P0202 - Injector Circuit-cylinder 2, DTC P0203 - Injector Circuit-cylinder 3, DTC P0204 - Injector Circuit-cylinder 4.

STEP 3. Check the ignition timing.

1. Refer to On-vehicle Service - Ignition Timing Check.

Q: Is the ignition timing normal?

YES: Go to Step 4.

NO: Check that the crankshaft position sensor and timing belt cover are in the correct position. Then confirm that the malfunction symptom is eliminated.




STEP 4. Using scan tool MB991958, check data list.

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. Check the following items in the data list. Refer to Data List Reference Table. Datal List Reference Table
a. Item 5: Intake Air Temperature Sensor.
b. Item 6: Engine Coolant Temperature Sensor.
c. Item AC: Cylinder 1, 4 Heated Oxygen Sensor (front).
d. Item AD: Cylinder 1, 4 Heated Oxygen Sensor (rear).
e. Item AE: Cylinder 2, 3 Heated Oxygen Sensor (front).
f. Item AF: Cylinder 2, 3 Heated Oxygen Sensor (rear).
g. Item BB: Barometric Pressure Sensor.

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

Q: Are they operating properly?

YES: Go to Step 5.

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

STEP 5. Using scan tool MB991958, check data list.




1. Turn the ignition switch to the "ON" position.
2. Check the following items of data list. Refer to Data List Reference Table. Datal List Reference Table
a. Item AC: Cylinder 1, 4 Heated Oxygen Sensor (front).
b. Item AE: Cylinder 2, 3 Heated Oxygen Sensor (front).
- Voltage should fluctuate between 0 - 0.4 volt and 0.6 - 1.0 volt while idling after the engine has warmed-up.

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

Q: Are they operating properly?

YES: Go to Step 7.

NO: Go to Step 6.

STEP 6. Check the fuel pressure.

Refer to On-vehicle Service - Fuel Pressure Test.

Q: Is the fuel pressure normal?

YES: Check the following items, and repair or replace the defective items.
a. Vacuum leak.
- Broken intake manifold gasket.
- Broken air intake hose.
- Broken vacuum hose.
- Positive crankcase ventilation valve does not operate.

b. Injector clogged.

Then confirm that the malfunction symptom is eliminated.

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

STEP 7. Check the fuel pressure.

Refer to On-vehicle Service - Fuel Pressure Test.

Q: Is the fuel pressure normal?

YES: Check the following items, and repair or replace the defective items.
a. Check the ignition coil and spark plugs.
b. Check the EGR system.
c. Check compression pressure.
d. Check the fuel filter or fuel line for clogging.

Then confirm that the malfunction symptom is eliminated.

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