Fault Code P0300

[Pachanga02]

Thank you I'd appreciate it.

 

[Gmc lovin75]

Those just look like 80K mile spark plugs to me. Did you replace the plugs and the wires already??

Was their oil on the plugs or in the plug sockets? Are you loosing/consuming any oil between changes?

The plugs on the left looked nothing like the other ones, they were covered in oil a gunk and the other ones looked normal to me

 

[Gmc lovin75]

I'm not really sure which one was changed and I can't seem to find my receipt right now. If it shows up I'll let you know

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How did they figure out that it was the o2 sensor?

 

[SLCHOE]

Whatever bank that had the soot covered plugs had that bank's upstream O2 sensor data skewed. Fuel trims are bank specific and can be adjusted individually. The right side plugs looked ok. The left side plugs were obviously overly rich and fuel fouled. My guess is that it had a bad O2 reading very lean (low mV) and the PCM was compensating via fuel trim on that bank to try to get it within specs. PRoblem was in actuality the air/fuel mix was correct but the O2 was reporting incorrectly lean so the PCM was adding more fuel where it wasn't needed thus the misfires/plug condition.

 

[Pachanga02]

I wonder if this is what's happening with mine??? Is there a way to check if the 02 sensors are bad?

 

[SLCHOE]

I wonder if this is what's happening with mine??? Is there a way to check if the 02 sensors are bad?

If you have a scan tool that can real live data from all of the O2's then yes. Graphing data capability is even better.

Very lean mixtures will read close to 0 millivolts. Very rich mixtures will read near 1 millivolt.

Watching the live data of the upstream and downstream O2's you can disconnect a vacuum line such as the vacuum hose going to the brake booster and expect the mV to go very low. With the same hose disconnected, you can supply fuel (carb or brake cleaner/ propane) into the same hose and expect the O2 to go very rich (near 1 mv), If all O2's respond appropriately, you can 95% use them as a sure data point to do further diagnostics.

 

[Pachanga02]

I have a bb efilive scanner. I'll try to record and post it or try to understand the readings. Thanks