The historical critical method is a secular method of examining scripture that attempts to enforce modern historical approaches on reading scripture. So anything that cannot be explained using naturalistic scientific theory is automatically discounted. So essentially, any miracle or prophetic pronouncement is assumed to be either mythical or added into the text later, etc. Orthodox Christian scholarship rejects this approach to examining scripture.
The historical grammatical method is a faithful means of reading scripture. The historical grammatical method looks at the grammar and syntax of a given passage and examines the passage according to the cultural norms and historical events of the time in order to derive the original intended meaning out of the text. This method assumes that when miracles, for example, are reported by the gospel authors, they are reporting what they saw and experienced and that these aren’t just later myths added into the text. This is more in line with faithful exegetical reading of scripture. I think it is actually the historical grammatical method that you are thinking about.
I hope that clarifies the difference in the two approaches to scripture.