13A-HESITATION, SAG, STUMBLE, POOR ACCELERATION OR SURGE

Inspection procedure 14: Hesitation, sag, stumble, poor acceleration or surge

COMMENT

Defective ignition system, abnormal air/fuel ratio, poor compression pressure, etc. are suspected.

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

Fuel pump system failed.
Ignition system failed.
Poor compression.
EGR system failed.
Improper operation of the PCV valve.
Vacuum leak.
Clogged air cleaner.
Clogged exhaust system.
CVT 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

note

To protect the CVT, the TCM outputs, into the ECM, the request signal to reduce the engine torque according to the operation condition. Based on the signal, the ECM closes the throttle valve, retards the ignition or carries out fuel cut. At that time, the engine output seems to temporarily reduce, but there is no malfunction.

STEP 1. Check if the EGR valve sounds during initialization.

Is the initialization sound heard in the EGR valve?

Go to Step 2.

Refer to GROUP 17, Emission Control - Exhaust Gas Recirculation (EGR) System - EGR Valve (stepper motor) Check

STEP 2. 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.

Is any DTC set?

Refer to, Diagnostic Trouble Code Chart

Go to Step 3.

STEP 3. Using scan tool MB991958, read the diagnostic trouble code (DTC).

note	When the CVT has a malfunction, the TCM might output the request signal of reducing the engine torque in order to protect the CVT.

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

(2) Read the TCM-DTC.

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

Is the TCM-DTC set?

Refer to GROUP 23A, Diagnosis - Diagnosis Code Chart

Go to Step 4.

STEP 4. Using scan tool MB991958, check actuator test.

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

(2) Check the following item in the actuator test. Refer to Actuator Test Reference Table

Item 1: Injectors

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

Are thy operating properly?

Go to Step 5.

Repair or replace it. Then confirm that the malfunction symptom is eliminated.

STEP 5. Check the ignition timing.

(1) Refer to GROUP 11A, On-vehicle Service - Ignition Timing Check

Is the ignition timing normal?

Go to Step 6.

Check for installed conditions of the timing chain. Then confirm that the malfunction symptom is eliminated.

STEP 6. 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

Item 5: Intake Air Temperature Sensor
Item 6: Engine Coolant Temperature Sensor
Item 11: Accelerator Pedal Position Sensor (main)
Item 12: Accelerator Pedal Position Sensor (sub)
Item 13: Throttle Position Sensor (main)
Item 15: Throttle Position Sensor (sub)

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

Are they operating properly?

Go to Step 7.

Repair or replace it. Then confirm that the malfunction symptom is eliminated.

STEP 7. Check the fuel pressure.

Refer to, Fuel Pressure Test

Is the fuel pressure normal?

Go to Step 8.

Repair it. Then confirm that the malfunction symptom is eliminated.

STEP 8. Check the spark plugs.

Refer to GROUP 16, Ignition System - On-vehicle Service - Spark Plug Check and Cleaning

Are there any abnormalities?

Replace the spark plug. Then confirm that the malfunction symptom is eliminated.

Go to Step 9.

STEP 9. Check the ignition coil.

Refer to GROUP 16, Ignition System - On-vehicle Service - Ignition Coil Check

Are there any abnormalities?

Replace the ignition coil. Then confirm that the malfunction symptom is eliminated.

Go to Step 10.

STEP 10. Check the positive crankcase ventilation system.

Refer to GROUP 17, Emission Control - Positive Crankcase Ventilation System - Crankcase Ventilation System Check

Is the positive crankcase ventilation system normal?

Check the following items, and repair or replace the defective items.

Vacuum leak.
Clogged air cleaner.
Clogged exhaust system.
Check if fuel is contaminated.
Check if the injectors are clogged.
Check compression pressure.
Check if the foreign materials (water, diesel fuel, etc.) got into fuel.

Then confirm that the malfunction symptom is eliminated.

Repair it. Then confirm that the malfunction symptom is eliminated.