Hello all,
It has been like a year since I last posted. New job, new house, lack of money have all kept me from my vehicles.
Anyway, a guy I work with is having trouble with an engine swap and asked me for help. He has a 94 1/2 ton 2wd 4.3 auto that dropped a valve. He couldnt find a motor locally but he found an 89 4wd with a 5.7. He switched the engine and PCU but is having some problems with how it runs and the A/C doesnt seem to work (it did before the swap and he never disconnected the lines) Does anyone know where I could find, or does someone have wiring diagrams for one or both of these trucks. If they were available online that would be great. I think I could help him track down what is wrong if I had some schematics. Any help would be much appreciated.

The wiring schematic from and earlier year will be different in some areas such as the set timing connector was moved to the interior side of the firewall in 1994.

He has a 94 1/2 ton 2wd 4.3 auto that dropped a valve. He couldnt find a motor locally but he found an 89 4wd with a 5.7. The first problem that comes to mind is: Is far as I know all 1994 ½ ton auto trans pickups use a “PCM” which shifts the transmission and the 1989 uses an ECM which does not control the transmission shifting.

Did he get a PCM for a newer 350 truck?

Most likely all that was needed is a prom (chip) change. Is that what he did?
Was this equipment for a truck with AC?

Find out if he used the TBI unit from the donor 350. The TBI units look the same but they have different size injectors in them.

Hmm, He said that he changed the prom. I assume he is using the TBI from the donor. Will the different size injectors cause it to run poorly? I still haven't found a wiring diagram for either truck.

Will the different size injectors cause it to run poorly? Yes, the injectors have different flow rates (how much fuel they inject) and the correct flow rate must be used for the correct size engine.

Hmm, He said that he changed the prom. The prom not only has to be for the correct size engine, it must be for the correct application – vehicle and equipment.

I still haven't found a wiring diagram for either truck.
Do you have a specific wiring question or area you need to know about?