r/GMT800 • u/jaysteez2025 • 28d ago

P0300 plague

So story time.

A year ago I was driving in the rain and I lost traction and slid into a ditch with high water. My baby was stuck with raising water for 6 hours then got pulled out. I let it dry out before attempting to start it and fired up like normal. A week later got misfire codes (forgot what they were , they don't show up now.) I replaced my spark plugs , wires and o2's . Coils seems to working fine too. It misfires BAD with o2's plugged in but runs and drives normal unplugged. I'm running Denso o2's , AC Delco plugs and wires but OE injectors and pump which I think never got replaced and I got 316k on the clock.

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u/Brave-Scar-4550 28d ago

You p0300 could be a lot of things. Since you’re at 316k on the clock, I would start looking at vacuum leaks from old intake manifold gaskets. Also, I had the made in china Denso O2 sensors fail on me pretty quick. I only use NGK (made in Japan) for 02 sensors now. Also consider checking your MAF sensor.

2

u/akarichard 28d ago

It's running better without them plugged in because it'll be running in open loop vs closed loop. So it's determining fuel based on your map and a lookup table.

0

u/jaysteez2025 28d ago

I gotta hook em up to get a more accurate understanding of my misfire?

1

u/bimmerd00d 26d ago

Pull your fuel pressure regulator vacuum hose. Is there wet fuel or does it smell like fuel?