I have search this place but haven't figured out my problem. I changed the distributor cap, wire and spark plug. It is still misfiring and giving me code P0303. I'm getting so frustrated w/ this Blazer.

 

Been there,
First thing that comes to mind... Did you use ACDelco parts? Cap, rotor, spark plugs? Have you physically checked for a strong spark from the number 3 plug wire to the number 3 spark plug? By using an Ignition Tester (Calibrated For HEI Ignitions)?


If you're confident that it's not ignition related then move onto researching threads on symptoms regarding leaking fuel pressure regulators and also the spider injector.


I was also getting a code P0303 - "Cylinder 3 Misfire Detected" and after checking and eliminating one part after the next, I eventually pulled the upper manifold and replaced the entire spider injector assembly with regulator and since haven't had any further issues with misfire or with any codes whatsoever.
My Blazer is a 2003, so it came from the factory with the upgraded MFI, but it doesn't matter, everything fails eventually.
After replacing the MFI, I now get twice the fuel mileage, smooth idle and an increase in power. It's worth every penny of the $300 cost of the new MFI, and was fairly easy to do in my garage without any help. There's several very well made YouTube videos that explain step by step details covering the project.

 

I did not use AC Delco parts but mainly b/c I was in a pinch and was desperate to get my car running. I did use an ignition tester similar to the one you post and everything looked fine. Would it be wise to try and clean my injectors using some kind of cleaner? Maybe I just have 1 clogged injector so it's not getting enough fuel. I really don't want to buy a $300 part and not have it be my problem. Is there anyway to test those?

 

I did a compression test tonight and everything looked ok. I put everything back together drove it around the block just to hope it magically fixed itself. It didn't but I did have a weird smell coming from the car when i got back. It smelt like fireworks I guess would be the best way I can describe it. My only guess is my spider is bad and now time to replace it. Any suggestions on which one to get?