Hello! I'm new to this forum and have read thread after thread trying to find an answer to my issue and have had absolutely no luck. I'm at my witts end and going crazy. I have a 2000 Chevy Blazer 4.3 2WD. About a month ago it started to have a very intermittent misfire when going up a hill or reaching highway speeds. My check engine light would flash while misfiring, and then stay on. It has a P0300 & P0305 code. I started with replacing all of my plugs, wires, cap & rotor button. The issue persisted and had become less intermittent and something to expect every time I would go uphill. It actually died going up a large hill and I had to have it towed. I then tested fuel pressure and everything was fine with it. I went ahead and replaced the spider injection, no difference. I then removed the cap and rotor button again. The post on the cap had scrub marks where the rotor button was hitting them at an angle. My distributor had more than normal play in it so I went ahead and replaced it and got a new cap & rotor button. This did not take care of the issue. I then swapped the #5 plug to #1 to see if the misfire would follow the plug and it did not. It stayed on #5. I went ahead and replaced the coil as well. My gas mileage has plummeted, and my vehicle has become virtually undrivable because I live in the country with tons of hills. I drove it today, went up a hill and once again it started misfiring like crazy, chugging, losing power and would not accelerate. I pulled over and it immediately shut off. I tried restarting it and it started right back up but was still chugging/misfiring. The misfire is only on cylinder #5. I have not done a compression test yet because it's not a dead misfire, it idles perfectly. This vehicle was meticulously maintained by the previous owner, but it did sit for a year before I got it. I have been driving it for about 14 months with no issues. If you have any advice or what I should do next please help me.

 

Start by checking Cam Sensor (CMP) Retard with a capable scanner. This should be zero +/- 2 degrees. If you don't have a capable scanner that will read live data and CMP Retard, come back for a couple of $35-$40 solutions.