i just replaced my heater core in my 92 pontiac transport 3.8 when i went to start her she started missing like crazy. the plugs,wires,coils and fuel injectors are working fine. and low or high speeds she misses and the trans is shifting hard on take off. could my e.c.m be wet?
Leave any vacuum hoses off? Did you reconnect all the electrical connectors you disconnected? My point is you should be going over stuff you did as you replaced heater core, assuming symptoms started right after this operation. I know how demoralizing this can be, but RELAX and go SLOW, and eyeball as much as possible before you decide to pull out dash again. Good luck; post back.