4.3L V6: Z, W, and X, what are the differences?

The 8th character in the VIN tells what engine was originally installed in the vehicle. There are 5 different types of 4.3L fuel injection systems and 4 different types of engine control systems used on them.

The “Z” engine code, 1987 through 1995, uses Throttle Body Injection, (TBI) and OBDI engine controls. It uses two injectors mounted in the throttle body. The injectors alternate when firing. Each injector feeds every other cylinder in the firing order. With the engine running, fuel pressure must be 9psi to 13psi.

The “W” engine code, 1992 through mid 1995, uses Central Multiport Fuel Injection, (CMFI) and OBDI engine controls, (late 1995 engines are controlled by OBD1.5). Both systems use one centrally located injector inside the plenum. There are 6 fuel lines connected to the injector; at the other end of each line is a plastic nozzle with a spring loaded poppet valve. Each line is routed to a machined passage in the lower intake manifold that leads to the back side of the intake valve. The injector is “batch fired” meaning it feeds all cylinders simultaneously. Fuel pressure spec for 1992 through 1994 is 55psi to 61psi with the ignition in the RUN position, engine OFF, and the fuel pump running. It must remain above 50psi for 3 to 5 minutes after the fuel pump shuts off. Fuel pressure spec for late 1995's is 58psi to 64psi with the ignition in the RUN position, engine OFF, and the fuel pump running. It must remain above 53psi for 3 to 5 minutes after the fuel pump shuts off.

The “W” engine code on 1996 and newer uses Central Sequential Fuel Injection, (CSFI) controlled by OBDII engine controls. There are 6 injectors that are centrally located inside the plenum. There is a fuel line connected to each injector; at the other end of each line is a plastic nozzle with a spring loaded poppet valve. Each line is routed to a machined passage in the lower intake manifold that leads to the back side of the intake valve. The injectors are fired sequentially, just like the firing order of the engine. With the ignition in the RUN position, engine OFF, and the fuel pump running, fuel pressure must be 60psi to 66psi and must remain above 55psi for 3 to 5 minutes after the fuel pump shuts off.

The “X” engine code was available starting in 1999. It uses Multiport Fuel Injection, (MFI) controlled by OBDII engine controls. This system is nearly identical to the CSFI system both in appearance and operation. It has one substantial improvement inside the plenum. The poppet valves were eliminated and the injectors were relocated out to the machined passages in the lower intake manifold. The injectors are fired sequentially, just like the firing order of the engine. With the ignition in the RUN position, engine OFF, and the fuel pump running, fuel pressure must be 60psi to 66psi and must remain above 55psi for 3 to 5 minutes after the fuel pump shuts off.


OBD Connectors:

http://i561.photobucket.com/albums/ss58/cwhook/Diagconnectors.jpg





TBI:

http://i561.photobucket.com/albums/ss58/cwhook/43LTBI.jpg





CMFI:

http://i561.photobucket.com/albums/ss58/cwhook/CMFI.jpg





CSFI & MFI:

http://i561.photobucket.com/albums/ss58/cwhook/CSFIEngine.jpg

Thanks, I believe that will be helpful for many.

I'm really only familiar with the 92 W, CMFI, 4.3 engines, & I've wondered about the differences i them as well as what they look like under the hood. Now I know just a bit more about them.