chas:

If you will examine the plumbing at the dual pump installation, it's likely that you will find that the first pump out of the tank feeds into the second pump. Why are the pumps in series? To raise the fuel pressure above that which one pump can generate. [The volume is unchanged.] The higher pressure is required for the KE-Jetronic (CIS-E) system. The '87 has KE, the '85 does not. Hence, the '87 must retain a dual pump supply.