Engine - Multiple Cylinder Misfire
SUBJECT: 4.0L Multiple Cylinder Misfire
MODELS: 1999 - 2004 (WJ) Grand Cherokee (All Markets), 2001 - 2004 (WG) Grand Cherokee (International Markets), 1999 - 2004 (TJ) Wrangler, 1999 - 2001 (XJ) Cherokee
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)...
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. Download File PDF
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