I picked up a 96 S-10 Blazer for cheap and was told that the plugs were original to it. It did not have a misfire. I got new plugs for it and after changing them, it has a misfire. I pulled them all back out and made sure that they were gapped correctly (and they were), so I changed the wires thinking that maybe one of them got pulled on instead of the boot (16 year old son was helping/learning). It is still misfiring... any ideas?

 

distributer cap and rotor ????
firing order correct ? you didn't accidently mix up 2 wires
If you still have an old spark plug swap it out cylinder by cylinder


A "misfire" and also be a compression issue
I chased my tail trying to find a misfire on a buick roundevous
It had pulled a rocker stud but showed up as a misfire

 

I explained what i know of the vortec ignition system in detail earlier today and it may help you too.
Heres the thread
https://blazerforum.com/forum/2nd-ge...estions-85485/
Hope that works.
Basically what you need to know is that you need to replace all ignition system components with high quality name brand parts like AC Delco and Delphi, (I use NGK plugs though because ac delcos have failed me a few times) over the counter store brand parts are about 25% quality of factory parts in my opinion, if you replace one part with the stuff thats garbage right out of the box then the rest of the system cant function properly.
Distributor caps are a real problem with these engines so thats a good place to look.
On the plugs, i had a set of delcos once that all had the same number printed on them but had different numbers of stripes, ribs and lenghts of the ceramic insulator and threads and steel bodies were also different depths and lenghts, discovered this after installing them and it ran like crap, parts store warrantied them, never used delco plugs again, never had another problem with plugs either, totally my opinion, sure some agree and some dont and thats totally cool, just sharing my experience to help out the next guy.
Anyway check out that thread, it may help you understand more about the beast you are dealing with
Also double check for mixed up wires, the numbers are embossed on the distributor cap and are not in order front to back.

 

I changed everything one by one to be sure that I didn't mix up any of the wires. I took it and had it scanned and they said it was a cylinder 3 misfire. Would changing the plugs cause a problem with the cap or rotor?

 

I didn't purchase the spark plugs, I was unsure exactly what to get, so I sent a guy to get them. Apparently he bought Autolite XP Iridium plugs, so then they might be the culprit? I am going to get some AC Delco when I get paid and see if that corrects the problem. If not, I'll go from there, thanks so much!
Also, one more question, when I go to get the AC Delco or NGK plugs, do I need platinum or iridium or are they just trying to make more money off of me for no reason?

 

iridium

 

I suggest delco plugs and nothing else in a GM
anyone selling them can give you the exact same part number that it left the factory with

 

One time I changed plugs in my SIL minivan. Had a bad misfire under load after. Since I'm so smart, I said it's the fuel filter. Then I broke the fuel pump fitting getting the filter off. After I replaced the filter, and pump, I still had the misfire. Replaced all the wires.

Finally, after a couple days and $300 later, I discover I had cracked the porcelain on one of the plugs I had just installed, and it was grounding out on the exhaust manifold.

So, double check what you just did when problems show up right after you changed something.