engine cranks but wont start, spark plugs get wet, smells petrol when engine is cold

1.5 petrol engine. will only start if pull the car using a tow rope and runs fine. if the engine is warm could be restarted but if the engine is cold wont start even if I'm taking off the spark plugs for drying. A mechanic told me that it is the timing chain strertched but is expensive and I'm not sure about that just cause the engine runs great once started. When checked the car using a diagnostic scanner we've got a cranckshaft sensor fault and nothing else.