Although computers and artificial intelligence have been proposed as tools to facilitate the evaluation of student essays, they are not specifically developed for Malaysian ESL (English as a second language) learners. A marking tool which is specifically developed to analyze errors in ESL writing is very much needed. Though there are numerous techniques adopted in automated essay marking, research on the formation and use of heuristics to aid the construction of computer-based essay marking system has been scarce. Thus, this paper aims to introduce new heuristics that can be used to mark essays automatically and detect grammatical errors in tenses. This natural language processing technique can be applied as part of the software requirement for a CBEM (Computer Based Essay Marking) system for ESL learners. The preliminary result based on the training set shows that the heuristics and rule-based approach is useful and can improve the effectiveness of automated essay marking tool for writing in ESL.