[MiraclePieCo]

Originally Posted by 1project2many

Huh? Sophisticated diagnostic equipment? The ecm on a '91 350 is pretty basic stuff. You can read trouble codes with a paperclip! Most of the diagnostic tests for that ecm are available in "no scan tool available" format which uses a DVOM and simple observation testing to complete a diagnosis. The computers are programmed to run with five sensors (throttle position, coolant temperature, knock sensor, crank rotation, and vehicle speed) and the engine will usually run with any but the crank rotation sensor failed. It sounds like you don't want to learn about computerized systems, but the OBDI vehicles really aren't that bad.

I've learned the hard way about EFI systems. I learned from my local Chevy dealer that a simple idle adjustment can't be accomplished with a screwdriver, but must be a dealer service item at $150. I learned that each of those sensors you mentioned (and their associated wiring) is another opportunity for failure and sitting on the roadside in a Wyoming winter (a TBI car may run with a failed O2 sensor, but mine wouldn't go over 35 mph). I learned that ECMs fail totally with no warning whatsoever, and in the most dangerous of places. All my negativity against EFI is hard-learned from experience. It's an inter-related system; if one component goes out, it all fails. As my Chevy dealer mechanic says about EFI, "It's nice...when it works."