1996 K1500 P0300

I just bought a truck with a random cylinder misfire. Little back story on the truck, it was this guys brothers who passed away, he parked the truck and it sat for over a year. I went to look at it wouldn't start, i noticed a spark noise which i then saw coming off the distributer was chewed through by a rat. He grabbed one from another truck and it started right up. Truck was misfiring badly, which it threw the could p0300. Could the gas that is in it atm be bad we put a gallon of fresh gas in but still running rough. Thanks for reading and feel free to ask any questions.

Do you have a scanner that can read misfire counters? I’d try doing an injector balance test seeing if one is stuck shut from varnished gasoline. How long have you let it run after getting it started. Try adding more gas to it

i dont have a scanner for misfire counting unfortunately, i only got some cheap scanner. Do you know if any pc software i could use? would INPA work?

The gas itself could be the cause and as Cheryl suggested, could have fouled the injectors.

I would recommend you syphon the tank and put fresh gas before moving forward.

you can pull the injectors and pulse them on and off manually with a battery and looking at the spray pattern. If it looks like it’s atomizing the gas into a fine mist and not drizzling it out you can throw it back in.

Okay i put 5 gallons in still running rough cleared core came right back. Im going to check the plugs.

okay so the plugs were almost all fouled. Going to run down to the auto parts store and grab new plugs and wires.

I replaced all plugs and wires still missing and trowing the same code. Any idea of how i should go about testing components. The truck is definitely running rich as i can smell the gas out the exhaust pipe.

You'll need more data to see what's going on. If you don't have one already get one of the $34 (Amazon) obd2 scanners which will give you at least the live data and freeze frame data. Then post that info.

MAP 11''
Spark Advanced -22
02 Switching up and down voltages
STFT B1S1 10%
STFT B1S2 99.2%
STFT B2S2 50%
STFT B2S2 99.2%
LTFT B1 -3%
LTFT B2 -6%

Replace distributor cap and rotor? These were known for cross firing in the cap and causing issues.

derek.story wrote: MAP 11''
Spark Advanced -22
02 Switching up and down voltages
STFT B1S1 10%
STFT B1S2 99.2%
STFT B2S2 50%
STFT B2S2 99.2%
LTFT B1 -3%
LTFT B2 -6%

Was this taken at idle? The computer seems to think the engine is running lean, especially bank 2, so it's adding a lot of fuel to compensate. This could happen because of vacuum leaks, EGR stuck open, dirty MAF, clogged injectors or bad sensors (though all 4 o2 sensors are showing rich so I don't think it's them).

Yes it was taken at idle, I pulled the intake manifold. Lots of carbon buildup on top of the plenum. I also picked up a updaated spider injector from junk yard. Im going to swap the old one out and replace the gaskets.

Hi derek,

Like Stioc said, the ecm is seing a lean condition and adding fuel because of that.

I suggest you to stay focuse on it.

I would start with O2 sensor activity (just to verify ecm is seing the truth)

The (very limited) data suggests that the misfire probably is on bank 2 and that it might be due to a fuel supply problem of 1 or 2 cylinders.

You might want to kill cylinders one by one to make sure which one(s) won't contribute.

What is STFT b1s1? I think we have to see STFT b1 and STFT b2 without the s1 stuff. Long term indicates a rich condition with the negative numbers meaning it is pulling fuel.

Nissan Technician