I had the old Ford PCM on the bench and asked the question that probably comes up too fast: can I just replace this whole thing with a Raspberry Pi?
The Pi is tempting because it is understandable. It can run Python, log data, host a page, talk over the network, and generally make the system less mysterious. Compared to a 1990s automotive computer, it feels like it should be overqualified. But that is only true if the problem is compute. I do not think the hard part is compute.
The hard part is the edge of the system. The harness. The power. The grounds. The inputs. The outputs. The solenoids, sensors, references, drivers, and weird automotive voltage behavior. A Pi likes clean power and polite signals. A truck does not promise either.
What I checked first was not whether a Pi could run the logic. I looked at the connector and the pins I was already chasing. I was dealing with transmission-related codes and trying to understand what certain pins should measure. That made the problem feel less like a coding project and more like an I/O and failure-mode problem.
The failed assumption was that modern means better by default. A Pi is modern, but the original PCM is purpose-built. It already knows how to live in that electrical environment. It already has the connector and output stages and assumptions baked in. That does not mean it is good or easy to troubleshoot. It just means replacing it is not the same as replacing an old desktop computer.
The version that makes sense to me is using the Pi as an observer first. Let it log. Let it help me see what the old system is doing. Build a bench harness. Map the pins. Measure actual behavior. Capture when outputs change. Make the system legible before trying to take responsibility for it.
A real replacement would need protected power, conditioned inputs, proper output drivers, watchdog behavior, safe failure states, and a lot more testing than a weekend idea deserves. At that point I might be looking at a purpose-built ECU or industrial controller anyway.
Notes for next time: do not confuse compute with control. Start at the connector. Measure before replacing. A Pi that helps me understand the PCM is useful. A Pi pretending to be the PCM before I understand the truck is just confidence with extra steps.