This research conducted diagnostic assessment of problems in first-year undergraduates' English academic papers and tracked potential sources of the problems to the writing process and strategy use. Data collected include 339 term papers and interviews with 17 students. The samples were manually error tagged and marked against a detailed diagnostic checklist. The resultant textual features were then compared between two subgroups of Chinese students in the sample, namely, those graduating from local schools in Hong Kong (LS) and those coming from the mainland and sojourning in Hong Kong (MS). The analyses found both groups had the poorest performance in source integration and vocabulary use. LS used simpler words and made more grammatical errors, whereas MS attempted sophisticated vocabulary more successfully and used a wider variety of words and sentence structures. The difficulties they experienced, however, were rather similar, residing mainly at the researching, planning and formulating stages. Action control theory was introduced to interpret the self-regulatory strategies they adopted to cope with perceived difficulties during the writing process. Strategies to control goals, control resources, and control cognitive load were found to be the most typical. While these strategies could reduce their difficulties, only some seemed also to help with performance. A conceptual framework is proposed at the end to link writing products, process and self-regulatory control strategies as evidenced in the study. Four diagnoses are drawn with suggestions for practice and further research.