v6 P0304 missfire, 50PSI fuel pressure.

[Mechanicboy]

If I let my v6 LS warm up for a few minutes after completely cooling off it will set this code. I can hear/feel the miss at idle but it's intermittent and not predictable other then it will happen. I also feel it sometimes when I give it more then say 30% throttle while cold(cold being not at full operating temperature).
This issue mostly goes away once at full operating temp only occasionally happening.
I've changed the spark plugs and the coils. This seemed to fix it each time but then it would come back presumably after the computer had relearned the engine as I reset the computer after both services.
I have replaced the fuel filter, about ~7 months ago.
My idle fuel pressure is just a hair under 50 psi with a fully warmed engine, haven't been able to check the cold pressure yet because I just bought the gauge. Is 50PSI too much at idle? I can't check the pressure under load because the hose is to short to reach where I could see it and drive without taking the hood off. I did notice that the pressure seemed to respond slowly, but I'm not sure if it's the gauge or not.

I'm scratching my head here and trying to fully diagnose the problem instead of just throwing parts at it.

If I have to get under the intake again I think I might change the injectors and fuel regulator at the same time.

I also noticed that according to a scanner I have it says the my throttle position is 17/18% when at idle, is this normal?

Open to ideas.

 

[Lincoln Jealous]

sounds like your dedicated, so im sure youll get your answer

 

[Mechanicboy]

Update.

I've rulled out the egr valve as a vacuum leak.
I pressure test the fuel system again today and had 48PSI with the key off engine off. Started the engine and it droped to about 42 PSI. When I stab the throttle the pressure will quickly climb to ~50 PSI then drop to ~42 PSI. When I let off the throttle it will drop to ~38 PSI. After dong this I did notice that the fuel gauge needle will sometimes vibrate very fast ~r 2 psi up and down, maybe fuel pressure damper but don't think that would cause problem I'm having.

I had my uncle ride with me after testing the fuel pressure and I could barely get the car t act up and when it did it felt more like a ping then a miss. I use 91 gas so he was baffled after told him all i'd done to the car.

Any ideas?

 

[Mechanicboy]

Oh and I also tested for leak down of fuel pressure and it lost about 2psi after 10 mnutes or so.

 

[Mechanicboy]

Nobody?

I read on the 500 forums that this engine is known to ping sometimes and some have ran 1 tank chevron with techron and it cleared it up then went back to their old fuel of choice and everything stayed good.

I put some fuel injector cleaner and fuel system cleaner of different brands and no change.

I'm using Shell 91 gasoline, any have problems with it?

I'm also thinking of seafoaming my engine to clean it out, but I don't think carbon deposits are my problem because it does it when cold and at idle.

I also swapped the coil and spark plug from cylinder 4 with cylinder 5 to see if I can get a code to come back. So far I can't get a code to pop but the engine still has the same problem.