Why are automotive electronic products mounted on the engine?

Take a Ford Fuel Injection Control Module. I was asked to repair one, or two, and was given a document that explained how to perform a "repair". The document came from the internet, I did my own search and found a little more information. Anyway, I also noticed up until early 2000-2005 it appeared the modules were mounted on the manifold. Recent documents show them mounted on the firewall. I opened up the FICM and found that almost every component was starved for solder. The PCB's are close to 250mils thick and I'll bet at least 1 oz copper was used. There are large vias, at least two, on all power component pads - this is where the solder went. The module gets extremely hot, reflows solder, solder is wicked into the vias. The temporary fix, add more solder. Back to my original question, why was the module or any other control module is mounted on the engine?

Hi Bob,

One thought I have is that near the motor there are large fields due to the alternator, starter, etc. and electronic components mounted further away from the engine would require a longer cable harness. The harness would make for a nice coupling mechanism that could cause unwanted conducted/radiated immunity issues with a critical system like the computer.