runs very rich 5 mpg on 1990 Mazda B2600

changed plugs, cap,rotor,coil,distrbutor,o2sensor,water temp sensor,grounds on engine,different gas,set timing,could it be the ecm also swapped air flow sensor has a 2.6 engine

Asked by for the 1990 Mazda B2600
I am surprised it will run if it only gets 5 miles per gallon. Check fuel pressure, check regulated fuel pressure. Spec for fuel pressure is 64 to 85 psi but regulated pressure is 28 to 37 psi @ 20 inches of manifold vacuum, and 38 to 46 with no vacuum at the fuel pressure regulator.
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