I have a 305 motor in my k5. it was what i had at the time when i put frankenblazer back together. I converted a 79 motor to TBI with the intake and wiring. All the sensors had spots to put on to the motor to get readings and it worked great for a while. Now, since it is giving me the ESC code I'm curious. The ESC is only for a TBI 350. i believe the computer is for a 350 also. Is that the reason it is running like crap feeling like it is towing a trailer with no wheels only after it gets warm? i am planning on the Gen III swap as soon as i get some cash to buy the parts but i need this thing to run right until then. What do y'all think? Thank you!
The knock sensor, ESC, PROM, and maybe the injectors(?) are different for a 305 and 350 as I recall. Put 305 parts on there and it will probably run much better. Which I wouldn't want to do in your situation either, unless I had the parts already.
That's a fair number of differences, but unfortunately the 305's were running higher compression, with crummy heads, so were very prone to detonation. With the timing curve undoubtedly being different between the 305 and 350, it's entirely likely that the 305 is detonating with the 350 timing map, the knock sensor is picking it up, and retarding timing as much as possible, which will absolutely kill power.
Might not net you entirely what you want, but you COULD try retarding the base timing a couple/few degrees, and see what happens. Probably won't help across the board, but if you know exactly when your loss of power occurs, you should be able to see if that helps in that area.
It does seem kind of odd you weren't getting an ESC code before, have you looked that code up in the service manual (link is in my signature to them) to make sure that something like excessive knock/wrong module, etc can cause it, as opposed to solely something like an electronics failure or wiring issue?
