Okay so I’m kinda curious as to how tf this is happening. So my truck(85 F250 6.9 IDI swapped to 460ci) had an electronic fuel pump added by previous owner and it’s added to a switch (red rocker, bottom right) obviously the fuel pump needs to be switched on to start the truck but my question is actually when I turn the truck off with the keys but don’t switch the fuel pump off the engine still runs, clearly still causing detonation in the cylinders as if the truck was still running normally, what could cause this? Am I just stupid and distributors on old carb engines are fired differently than an electrical signal from an ECU (I’m pretty sure there is no ECU but I guess I just never thought about how they work w/o one)? If so how exactly do they work? This is my first carbureted car and first V8 so sorry if this is just dumb but I’m trying to learn more and more
If it’s a 6.9 idi then it’s a diesel and it’s not carbureted. The pump is still feeding the engine fuel and therefore the engine is still running. They run off compression and not a spark igniting the fuel like a gas engine. As long as it turns off when you turn the fuel pump off you should be fine. Older mechanical diesels can “run away” which is where they keep running even with the key off and this eventually leads to the engine destroying itself.