Originally Posted by
dave w
Basically the TBI Trucks, Suburban's, Astro Vans from 1987 to 1990 used the same ECM / Wiring Harness. To provide the lowes cost TBI conversion, the aftermarket focused on the early versions of TBI to support. Nothing wrong with using 1991 and newer TBI parts. It's can be complicated if all the TBI parts are not from the same donor vehicle after 1990.
The 1995 NV4500 most likely has the 40 Pulses per Driveshaft Revolution VSS, which feeds a converter know as a DRAC to produce 2000 Pulses per Mile input to the computer. 1987 to 1990 computers require also require a VSS with 2000 Pulses per Mile. In most aftermarket stand alone TBI wiring harness (1987 ~ 1990), the "Park" switch input to the computer is grounded so the need for a VSS is eliminated. Using the VSS makes for a much better TBI conversion, but a VSS is not absolutely necessary for a TBI swap.
The software and hardware for the 1987 to 1990 TBI is the simplest to learn and work with. After 1990 the TBI software and hardware, especially (1993 ~ 1995), is not so simple.
dave w