Hello from a newbie. I just bought a 2002 4.3L 4WD from a guy who was told by a mechanic that he had a blown head gasket as the vehicle kept overheating. My brother and I took it apart, believing it to be the intake gasket, which was clearly the case when we found the gaskets destroyed. At the same time, we replaced the distributor cap and rotor, as well as the thermostat, PCV valve, and some hoses. Everything seemed perfect, including the running temperature, but when I went to get the vehicle smogged, I failed with a 300 random misfire error. So back to checking the timing, and while at, replace the spark plug wires as it's got 90K miles on it. While we tried to use the two lines on the harmonic balancer for TDC and lined up the paint line with the two dots on the distributor, it turned out we couldn't use the harmonic balancer lines for TDC, evidenced by a compression test. We ran an OBD test again and the computer showed that we were now misfiring only on cylinder #1, which was great as it was no longer a 300 code, but still 301. So we replaced the one spark plug and put in some fuel injector cleaner, and I'll have to put some miles on it before I can test it again. Here's my question: someone mentioned "running the crap out of it and putting in Seafoam" after doing an intake job. Will this help? Does anyone else have any advice? Thanks!

 

Did you run a compression test on the motor?

 

Not yet. Will do that next.