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- Engine & Transmission (https://blazerforum.com/forum/engine-transmission-35/)

- - P0300 p0404 (https://blazerforum.com/forum/engine-transmission-35/p0300-p0404-98177/)

Bought blazer with p0305 misfire in cylinder 5. Well now its saying p0300 and p0404 which is multiple cylinder misfire and EGR valve. The previous owner replaced all the spark plugs, plug wire, distributor cap and rotor. Wondering what it could possibly be and where to start

Need more info... What year at least?

I’m sorry yeah it’s a 2000 it’s got about 96,000 miles on engine

I would start by checking fuel pressure. Assuming your 2000 has the original (or at least original style IF it's been replaced before) fuel injector "spider" assembly, it has what are called a "poppet" style injectors for each cylinder. They require a specific amount of fuel pressure before they will "fire" off and inject fuel into the intake runner they're pointed at. If the injector nozzle either gets partially internally clogged (from bad or dirty gas) or the fuel pump is beginning to go, OR the fuel pressure regulator that is mounted to the assembly inside the intake starts to leak, fuel pressure at the poppet injectors can drop and cause them to not operate correctly and can easily cause multiple cylinder misfires.

Just my $0.02

Also take off the EGR valve and make sure there's not a piece of carbon stuck in it and holding it open.