Blazer Forum - Chevy Blazer Forums

Hello,
I have an 89 Blazer (full size) 350/5.7L & it has all of a sudden started to ruin really rough. I had been in the process of getting it to pass emissions & I had it running really good but then something happened. I had done the full tune-up prior to this issue including changing the entire distributor. It was running great after that but it wouldn’t pass emissions so I ran some 44K through it & drove it for the day. The next day right after I got off of the highway it started running rough. I pulled code & got a code 42. I then had the coil tested (good), replaced ignition module, spark control module, replaced spark relay, checked wires & connectors & they seem to be ok…please help!