Hello Chevy Forum, I'm trying to figure out the cause of my 1989 Chevy Scottsdale k2500 misfiring and running horribly but only when the electronic spark control bypass is plugged in. If I leave it unplugged the truck runs fine it's just a little gutless. It acts like the ECM is bad because there is no codes being thrown. I've checked the throttle position sensor the map sensor the coolant temp sensor and I just recently installed a new knock sensor. also new plugs wires and distributor were installed by the previous owner and I checked, the distributor is in correctly. If anybody has heard of this problem before and knows what the answer was or if anybody has any thoughts I'd like to hear from you. Thank you