Does fuel pressure change when the engine is put in gear and rev'd up? If fuel pressure drops, that could be the problem, and should show up in the fuel trims. The 5V is probably full scale signal for the tank level gauge, regulated voltage from the ECM.

 

Fuel pressure and MAF will not cause one cylinder misfire. You can always disconnect MAF if you want to test it, ecu reverts to using only CPS, O2 sensor. If you replaced plug, wire, coil one at a time, then swap injectors with #3 next.

 

The fuel pumps on the D2 are definitely known to go bad, although not typically a full failure.

At 130k, my D2 would almost never start on the 1st crank. After testing fuel pressure, it was low. This was completely fixed after replacing the fuel pump. It's not a very fun replacement, but pulling the entire rear carpet does give you the ability to treat any body rust inside. Before fully reinstalling the components that hold the carpet down, you can cut a circular hole in the carpet for future pump access.

Before you order, know that there are 2 different types of pumps, and make sure to order the right one.

I'd recommend it as a preventative fix, even if the pump isn't the culrip.

 

The two pumps are for SAI or no SAI. Get the Bosch, I had to replace mine twice bc the fuel gauge was not working on it. As Extinct states, that may bot be the issue but it is cheap and easy enough that it is worth trying.

Logically, if you are getting low fuel pressure, that is before the injectors so all injectors are getting the same pressure. If one cylinder is low, then perhaps the injector is the issue. In my opinion they are enough of a pain to pull that I would just replace them. You can test them buy hooking up a battery and they will audibly click, that does indicated spray quality, but if they work at all. Mineral spirits is great for cleaning them if you want to clean what you have.

I did have one dead injector from an amazon kit, but once I connected it outside of the truck it fired up.

 

Quick update.

I did swap injectors, plugs, wires, and coils, all seperately. I was so optimistic I'd find the issue, but the misfire remained in cyl 1.

I've also done O2 sensors, and head gasket, and compression is good on all 8 cyl (within 5%). Fuel pressure seems to never quite get to 50 psi. I've seen 45 while cranking it, and I've seen 30 with the priming shot. So, I figured I'd throw a few new parts at it. I ordered a fuel pump assembly, a MAF sensor, and CPS.

I do wonder though.. Isn't the fuel pressure regulator vacuum driven from the throttle body? Looks like there's a sensor or something along the way, mounted on the left side if you're sitting in the trunk. Anyone got any info on that?

If none of that solves it I guess

 

Well since you have swapped injectors, coil, spark plug, spark plug wire, and check the compression on that cylinder all separately the only thing left that it could be is the ECU. Suggest you swap it with a different ECU to test

 

Not a bad idea. I don't have one laying around. But maybe a junk yard will.

 

FPR vacuum source is the intake manifold, requires less fuel pressure when the manifold pressure is low (high vacuum at idle), and more fuel pressure when the throttle is wide open. FPR tries to maintain a constant pressure difference between the fuel and the intake manifold so that fuel delivery is always linearly proportional to injector pulse time. The sensor on the fuel rail is to monitor fuel temperature, and is used to help start very hot engines (so hot that fuel could vaporize in the rail).

Let us know how the new fuel pump works out. Maybe check fuel trims before and after.

 

I am having a misfire on cyl 1 when I’m at temp and it only seems to happen in the summer. I get a pretty good stutter at idle. Nanocom picked up a single missfire on Cyl 4 after a few minutes but nothing else. It doesn’t do this when it’s cold and for a good while warming up. The thing runs immaculate.

I’ve not pulled plugs, but just ordered a set as a matter of course. I guess wires and coils will be next as I’m pretty positive mine is ignition related.

 

Regarding the original post, I just did fuel pump and MAF too. And you know what.. It runs good 80%of the time. Then.. Misfire, cyl 1, p0301. I have no idea at this point. But for you, I'd start on the ignition side.