The question is related to the question: detecting weak equivalences in a simplicial model category

Suppose that we have a simplicial model category $M$ and denote by $M^{f}$ the full simplicial subcategory of fibrant objects. Suppose that $R$ is a subcategory of $M^{f}$ such that for any object $m\in M^{f}$ there exists an object $r\in R$ such that $r$ is (zigzag) equivalent to $m$ i.e. $r$ and $m$ are isomorphic in $Ho(M)$ the homotopy category of $M$. Let $w: a\rightarrow b$ be a morphism in $M$ such that for any object $r\in R$ the induced map of simplicial sets $w^{\ast}:Map_{M}(b,r)\rightarrow Map_{M}(a,r)$ is a weak homotopy equivalence of simplicial sets. Can we conclude that $w$ is a weak equivalence in the model category $M$ ?

If $R=M^{f}$ this is true and is proved in Hirschhorn's book.

**EDIT :** The question is very general, and it should have a formal answer in case it is true. After trying all suggestions (in the comments and deleted answer) and reading Hirshorn's book I had the impression that maybe the answer to my question is **no**, and there should be a counterexample. In the Hirshorn's book the fact we test for all fibrant objects seems to be essential.