Engine - Multiple Cylinder Misfire: Overview
NUMBER: 09-003-03GROUP: Engine
DATE: Aug. 01, 2003
SUBJECT:
4.0L Multiple Cylinder Misfire
OVERVIEW:
This bulletin involves inspection of all engine exhaust valves and a decarbonizing procedure if necessary.
MODELS:
1999 - 2004 (WJ) Grand Cherokee (All Markets)
2001 - 2004 (WG) Grand Cherokee (International Markets)
1999 - 2004 (TJ) Wrangler
1999 - 2001 (XJ) Cherokee
NOTE:
THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 4.0L ENGINE (SALES CODE = ERH).
SYMPTOM/CONDITION:
The customer may experience an incident of engine misfire during certain vehicle operating conditions. The misfire may occur when the vehicle is operated between 80 - 112 KPH (50 - 70 MPH) and under light loading conditions, e.g. slight uphill road grades. This condition may occur at all ambient conditions, but is more noticeable when ambient conditions are less than 0°C (32°F).
If the vehicle is equipped with On-Board Diagnostic (OBD), a MIL illumination may also have occurred due to Diagnostic Trouble Code (DTC) P0300 - Multiple Cylinder Misfire. Various single cylinder misfire DTC's may also be present. If the frequency of misfire is high the Powertrain Control Module (PCM) may place the engine in "Limp-In" mode.
The misfire condition may be caused by one or more engine exhaust valves that are slow to close. Late closure of an exhaust valve may be the result of no valve rotation and associated build up of carbon on the exhaust valve stem.
DIAGNOSIS:
1. This condition may occur when the engine is not allowed to run at engine RPM's that are greater than 3,200 RPM. At 3,200 RPM or higher the engine exhaust valves will rotate if not impeded by high carbon deposits. Low engine RPM's and high carbon deposits are associated with short trip driving where the vehicle engine is not allowed to fully warm to normal engine operating temperatures. Cold ambient temperatures will increase engine warm-up time and add to the opportunity of carbon deposit build-up on the stem of the engine exhaust valve.
2. Verify that an engine misfire condition is present. Use of the DRBIII(R) during a road test, or a Co-Pilot data recording, may help to determine engine misfire and misfire counts. If carbon deposit accumulation is severe, then a cylinder leak down test may detect one or more cylinders leaking greater than 15%. Save any misfire DTC Freeze Frame Data that was stored for later misfire correction verification.
3. Verify that the engine misfire condition is not caused by faulty engine mechanical or electrical components.
4. If the engine mechanical and electrical systems are operating properly perform the Repair Procedure.
PARTS REQUIRED:
EQUIPMENT REQUIRED:
POLICY:
Reimbursable within the provisions of the warranty.
TIME ALLOWANCE:
FAILURE CODE: