I just bought a 98 Blazer with low miles 63 thousand super clean and appears to be well maintained. I just changed the plugs to AC Delco and Napa Beldon Wires. It looks like previous owner had receipt of replaced distributor cap recently at dealership. Vehicle seems to intermittent have extra exhaust noise, sounds like vacuum leak from lower left side of engine on occasion. Some times has really good responsive power and shoots up hills and some times really sluggish when exhaust is noticeably louder. Both manifold gaskets were replaced at 58k at dealership. I am wondering if manifold gasket issue, catalytic converter, fuel pump, fuel filter or vacuum leak that I don't know about? I am not sure what to narrow it down to and feel stumped and I don't want to start throwing money at it. I thought about taking it to the dealership and get it diagnosed and then fix it myself. Blazer liked new plugs and wires but I still got the same issue before plug and wire change. Starts great and idles good and runs good for the most part. Any help greatly appreciated.

 

maybe the catalytic converter? dad had one get stopped up on him with his '05. also had a code afterwards for a o2 sensor. dont know if one could have caused the other. he said he couldnt hardly get up to 50 mph and had to baby it to get it up to speed at all, flooring it just made things worse. oddly enough his '05 has less than 100K on it, while my wife's '97 has nearly 190k with the original converter. id check fuel pressure as well. not sure how you would check the converter, maybe drive it 5-10 miles and see if its excessivly hot. theres a way to diagnose a clogged converter using a vaccum guage, but i forget just what to look for when doing so.

 

The way i saw the exhaust shop test the converter was let it heat up then use a heat gun to measure the temp in the front half of the cat then measure temp in the back half of the cat. when mine was bad i think there was a 30 degree difference. i think the hottest temp was a little over 260, so if its over that then its probably bad. a vacuum leak would also cause a loss of power, i would open the hood with the engine running and try to listen for a leak. if you have some sort of short pipe you can use it to poke around in the back of the engine bay to pinpoint the leak. i heard using the pipe works pretty well for pinpointing where the sound is coming from.