I have been chasing a misfire in my 1999 Blazer since last winter. I parked it over the summer as it is my winter vehicle and now that the snow is flying I have been driving it with the misfire and its quite irritating and I’m sure hazardous to the engine.
Initially when the SES light popped I had 3-4 codes O2, MAF, and P0301 misfire in cylinder 1. I replaced the faulty sensors in hopes they were also causing the misfire. No luck. Then I replaced the cap rotor plugs and wires as well as a compression test on all the cylinders, still no luck, replaced the Ignition coil and Ignition control module and nada. Next I went to a local garage for “expert “advice they told me what I had suspected, my Spider injector is the problem and for a small fee of $800 they could fix it. Being the weekend mechanic I am I opted to DIY and saved $500 but the code is still reading a misfire but now it’s a P0300 random/multiple misfire. On a positive note with the new MFI the truck runs 100% better but you can still hear the misfire.
I was reading up in the forums and there were some cases the upstream sensors or the cat could be causing a misfire but wouldn’t they have their own error codes and there is no odd smell from the exhaust. Also why would it go from a P0301 to P0300 any advice would be appreciated.

 

What brand of ignition components (plugs, wires, cap, & rotor) did you use? Aftermarket brands tend to have misfire problems out of the box. AC Delco caps & rotors have a high reputation for quality on these trucks and don't cost that much more than the aftermarket stuff that has a reputation for failure.

What were the codes that were present, specifically? What codes are currently stored and/or pending?

 

I’m sure I bought the cheapest ones they had; the only code now is the P0300. I could have it checked again at auto zone but that’s the only one it had Monday evening.
I was thinking of changing out the plugs and wires to AC Delco but wouldn’t there have been the P0300 the whole time instead of the P0301 prior to the spider swap? Are there any additional changes that need to be made for the new MFI to work properly or should it have been good as a straight swap?

 

I have been fighting this same issue with my new engine. I replaced everything with Ac delco ignition wise and no luck slight misfire around 55mph then highway speeds (65-70) and its a hesitation/jerk..

 

http://www.amazon.com/Delphi-FJ10565...5140777&sr=8-1

Did you use this brand? I ju.st order it for our 1998

 

Would a map or Mar sensor be an issue?