(I'm not sure if this is the correct place to post this... Monitor, feel free to move.) Hi everyone, I'm new to this forum, and relatively new to the auto world. However, I do have some experience with doing semi basic repairs. I purchased a '93 Chevy K 1500, V6, 4.3L about a month ago and have steadily been working on common repairs (since the vehicle has been neglected for what appears to be years). The first problem that I had to get fixed was an exhaust leak. It had two leaks, one at the donuts and another on the manifold exhaust gasket. The former I repaired quickly, but I am still waiting to get it into the shop for repairing the latter. (I don't want to deal with taking apart the manifold exhaust myself). Anyway, when the mechanic looked at the truck and repaired the donuts (and did some welding) he told me that the engine also had a misfire on the right side of the engine. He was of the mindset that the chamber most likely had a leaking seal and that oil was fowling up the spark plugs. After I did some research and talked to a few people I replaced the plugs, wires, and cap. It desperately needed it too. Although my mileage increased with the new plugs and the first exhaust issue repaired, the misfire seems to stick around. I looked up how to get into the "check engine light" and got a code 33 and a code 45. That is, MAP signal voltage high and rich exhaust, respectively. After some research, I found that these issues can sometimes be related to an engine misfire, so I checked the MAP sensor and it came out okay. So I reset the ECM and that particular code went away. However, code 45 and the misfire are all still present. In trying to address code 45, I ended up replacing the EGR valve. It seems to run slightly better, but not significantly. My questions are these: Do you think that code 45 and the misfire might be related? If so, could it be a fuel pressure/EVAP/injector issue? Is there some possibility that the manifold exhaust leak scrambles the sensors and messes everything up? How can I verify a misfire and be sure that I'm not just hearing an exhaust "pop"? (although I think the mechanic was honest, I want to be sure myself, too). What does it tell me that the misfire is on one side of the engine and not random? Is it possible that it is a vacuum leak? If it is a seal within the engine and oil is getting into the chamber, how big of a repair is that? Can/should I do that myself? Finally, what should I look at first? I apologize for the length of this post, but I greatly appreciate any guidance at all. Whether it be what to look for, what to ask the mechanic, or how to address the repair. Thanks!