I have a 2000 Silverado with 5.3 nv3500. Been chasing this random miss fire code for months. Did the following. Smoke test for vaccuum leaks, all new plugs and wires, replaced mass air flow sensor, replaced fuel pressure regulator. I checked fuel pressure and it is reading low like 40-45psi . I’m thinking that is probably an issue. So would I need to replace the fuel pump? Don’t want to keep throwing parts at it if it’s not going to fix it. Would appreciate anyone’s feed back and help thank you !

 

That pressure does seem low for a non-flex-fuel engine. That's at idle? Can you stick your fuel pressure guage to your windshield with duct tape (may need a longer hose) and go for a drive. Do a few WOT accelerations and check fuel pressures. See if you can correlate the misfire with lower fuel pressure readings.

 

I got a new fuel pressure gauge and just checked it fuel pressure is sitting right at 50 psi at idle

 

Had the same issue. Replaced fuel injectors and no more P0300! Only had 2 bad ones but opted to just replace the set.

 

There's a guy that will clean, and flow test your injectors.
The OEM Delphi is good stuff. I'd rather spend money on GOOD parts than buy Xhinese sheeit that's swamped the market.
Derr Injection.

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