Let $W(x) = x^4 - 3x^3 + 5x^2 - 9x$ be a polynomial. Determine all pairs of different integers $a$, $b$ satisfying the equation $W(a) = W(b)$.
1. Given the polynomial \( W(x) = x^4 - 3x^3 + 5x^2 - 9x \), we need to find all pairs of different integers \( a \) and \( b \) such that \( W(a) = W(b) \).

2. Start by setting \( W(a) = W(b) \):
   \[
   a^4 - 3a^3 + 5a^2 - 9a = b^4 - 3b^3 + 5b^2 - 9b
   \]

3. Rearrange the equation to:
   \[
   a^4 - b^4 - 3(a^3 - b^3) + 5(a^2 - b^2) - 9(a - b) = 0
   \]

4. Factorize the differences of powers:
   \[
   (a - b)(a^3 + a^2b + ab^2 + b^3) - 3(a - b)(a^2 + ab + b^2) + 5(a - b)(a + b) - 9(a - b) = 0
   \]

5. Factor out \( (a - b) \):
   \[
   (a - b) \left( a^3 + a^2b + ab^2 + b^3 - 3a^2 - 3ab - 3b^2 + 5a + 5b - 9 \right) = 0
   \]

6. Since \( a \neq b \), \( a - b \neq 0 \). Therefore, we must have:
   \[
   a^3 + a^2b + ab^2 + b^3 - 3a^2 - 3ab - 3b^2 + 5a + 5b - 9 = 0
   \]

7. Let \( M = a + b \) and \( N = ab \). Substitute these into the equation:
   \[
   (a + b)^3 - 2ab(a + b) - 3(a + b)^2 + 3ab + 5(a + b) - 9 = 0
   \]

8. Simplify the equation using \( M \) and \( N \):
   \[
   M^3 - 2MN - 3M^2 + 3N + 5M - 9 = 0
   \]

9. Rearrange to solve for \( N \):
   \[
   8N = 4M^2 - 6M + 11 - \frac{39}{2M - 3}
   \]

10. Since \( M \) is an integer, \( 2M - 3 \) must be a divisor of 39. The divisors of 39 are \( \pm 1, \pm 3, \pm 13, \pm 39 \). Therefore, \( 2M - 3 \) can take these values.

11. Solve for \( M \) for each case:
    - If \( 2M - 3 = 1 \), then \( 2M = 4 \) and \( M = 2 \).
    - If \( 2M - 3 = -1 \), then \( 2M = 2 \) and \( M = 1 \).
    - If \( 2M - 3 = 3 \), then \( 2M = 6 \) and \( M = 3 \).
    - If \( 2M - 3 = -3 \), then \( 2M = 0 \) and \( M = 0 \).
    - If \( 2M - 3 = 13 \), then \( 2M = 16 \) and \( M = 8 \).
    - If \( 2M - 3 = -13 \), then \( 2M = -10 \) and \( M = -5 \).
    - If \( 2M - 3 = 39 \), then \( 2M = 42 \) and \( M = 21 \).
    - If \( 2M - 3 = -39 \), then \( 2M = -36 \) and \( M = -18 \).

12. Check each \( M \) value to find corresponding \( N \) and verify if \( a \) and \( b \) are integers:
    - For \( M = 3 \), \( N = 2 \), we get \( a \) and \( b \) as 1 and 2.
    - Other values of \( M \) may not yield integer solutions for \( a \) and \( b \).

13. Therefore, the only pair of different integers \( a \) and \( b \) that satisfy \( W(a) = W(b) \) is \( (1, 2) \).

The final answer is \( \boxed{ (1, 2) } \)