Invisions1

Just sprayed starting fluid on all injectors and around intake. No change in rpms.

rideredcr

A random misfire (P0300) with out any other codes can be a tough one to resolve, especially without a code reader. Break your diagnostics down into bite size pieces instead of bouncing around and chasing your tail i.e. ensuring your fuel delivery is within spec and functioning properly prior to moving on to the ignition system and then air leaks and MAF sensor (or whatever order you want to work through). I've been struggling to find the cause of my own P0300 code for 6 months now. Still no resolution on my end. Unfortunately for me mine is intermittent and all systems are functioning within manufactures spec. One thing I can tell you is eliminate as many factors as possible by proving the component or system is function properly and within spec.
Your starter fluid trick will not work because the computer will adjust for the added fuel faster than you can tell the rpms increased. If you have a scan tool you can watch your fuel trims go negative (computer removing fuel) if you are spraying starter fluid or propane near a vacuum leak.


Hopefully you have already done a tune up- New plugs and filters
Check your MAF to ensure its clean- a dirty MAF will lie to the computer and your fuel ratio (14.7/1 - 14.7grams of air for 1 gram of fuel) will be off
You verified fuel pressure was within spec but after the fuel pump turned off did your fuel pressure maintain for at least 30 min? If not, your fuel pressure regulator may be leaking.


I might be telling you something you already know but a misfire is related to 3 things:
Fuel- too much or not enough
Air- a lying sensor or vacuum leak
Ignition- something in the system is weak

Good luck!

Invisions1

I pulled and cleaned the the maf today with crc maf cleaner. Hooked back to scanner and still getting p300 code. I have done a tune up. Plugs.wires. A sensor that had a code near the rear axle. Do recall what is was called. Engine starts with ease and runs great with a slight vibration. Fuel mileage has increased since tune up. One note is that this vehicle sits for most of the year. When I did the fuel pressure test I noticed the fuel was a darker almost orange color. I have ran fuel injector cleaner and water remover thru it. When I bought it it had almost thirty thousand miles on it but after looking only had fifty engine hours on it and found out it had been pulled behind a motothome most of its life. So actual miles are probably less than eighty thousand. It has so much power on acceleration and passing I can't imagine it being a major issue. There's something simple I am missing. Thanks for the reply

Invisions1

One note I forgot to mention is during fuel pressure test once pump stopped pressure did drop a couple of pounds. Did not run during the test.

rideredcr

Oh and if you do end up purchasing a scan tool let me tell you there is a loooooooooooot of bad information out there on fuel trims. The bad information sent me down a bunch of wrong roads. Your long term fuel trim or LTFT is what you are most interested in when trying to diagnose issues. Anything from -10 to 10 is acceptable -5 to 5 is prefered. 0 is factory optimal. -10..... the computer is taking away 10% fuel from factory optimal because over time the O2 sensors see the engine running rich. 10....means the computer is adding 10% more fuel because over time the O2 sensors see the engine running lean.
Here is the part that screwed me. Your short term fuel trims or STFT are the deviation from your LTFT. So if your LTFT reads 10 and your STFT reads -8 then at that moment you are only +2 from optimal
STFT are the immediate response from O2 sensor
LTFT are stored/learned fuel maps that take a long time for your computer to relearn. The best way to reset LTFT...especially after changing a component or fixing a vacuum leak is to disconnect the battery for 30 min. The PCM will forget all LTFT data and be forced to relearn the next time you start your vehicle.

Now that I have confused you, Good luck!

Invisions1

Yes sir. I do believe you have succeeded in confusing me. I think I may take the rest of the night off and go back under dr Miller lites care.

rideredcr

Dropping a few pounds after pump stops is normal. A steady fall to zero or something close indicates a leak.
As for your mention of the amount this vehicle is driven, bad fuel and or contaminated fuel is definitely just one more reason an engine can misfire. The gas industry formulates our gas to last on average 30 days. After that is begins to degrade. Additives begin to dissipate and eventually your left with something that smells like paint thinner. If your gas is old, this would be my #1 suspect.

Invisions1

Another thing I have done is pulled one wire at a time off of the coils and noticed with each one a sudden struggle in the engine. After seeing the fuel after the pressure test I will drop the tank this weekend and drain and clean it. Hopefully will have a bit of good news on results. Thinking back it has sat this years from January until June with no starting

in2pro

+1 for the fuel pressure and I would agree too that fuel should never be ruled out, do what you can to get gas from a different station and/or evaluate where you got the last tank full if it was different from the usual.

Invisions1

Ran the tank down to three or so gallons. Dumped fifteen gallons of new fuel in. Reset the pc and headed home. No codes until I stopped at the house and let it idle. Finally got a p305 code. Did another reset and let her idle. Another p305 code. Was a pd code so never sent but only tested a few minutes.