What’s an average fuel Pressure you guys see on a 400? Purchased a little fuel pressure gauge I’m going to throw on car here sometime, just wondering about what it “should” be?
Car has developed a miss at higher RPM under load and will even backfire a bit and is just more hesitant then it used to be when getting on it. Trying to check everything I can. Need to get the timing/advance checked sometime here, but sure seems to run fine when just reving it up in neutral. Any simple ways to check a Cam, guessing pulling the valve cover and have someone turn engine over while measuring is about the best? Stethoscope sure sounds the same from cylinder to cylinder.

A stock type mechanical fuel pump should be about 5 to 6-1/2 psi. It will fluctuate every time the pump arm moves on the eccentric.

In order to see what it's doing while driving, place a T in the fuel line near the carb and run a fuel line up through the cowl then zap strap it to the windshield wiper arm. Connect the gauge to the strapped fuel line and position it so you can see it while driving. Do not run the gauge inside the cabin. Had the same problem myself a few years back and one of the members here at FGF gave me the suggestion. I did as instructed and found my fuel pressure dropping on hard pulls, thus my misfires at high rpm. New fuel pump solved the problem.

There are fuel pressure gauges for use inside the cabin out there, mechanical and electric, but they do not have fuel in the lines inside the passenger section of the car.

You could remove the rocker cover and set up a dial indicator on the top of the valve spring then turn the crank by hand and measure the amount of lift at the spring of each valve. If one was way off in regards to the rest it may indicate a flat lobe. If you have hydraulic lifters it wouldn't be accurate enough to tell the camshaft specs. Some lifters may have more oil in them than others with the engine not running. If you have solid lifters you could set the lash then use the dial indicator and a degree wheel to see what lift you have and when.

Uhhhh...check your fuel filter, had the same symptoms years ago and found the filter was the culprit (the one mounted at the inlet of the carburetor) and any other aftermarket ones you have installed.

Changed the inline fuel filter on my car this weekend and was surprised that line and filter were empty except a few drops in the filter, is that normal for the fuel to bleed out of there after sitting a couple days?

Put a fuel pressure gauge in right up near the carb and looks to be around that 6-7 psi idling and reving it up, arm in gauge really moves around like mentioned above, but sure looks to average around that 6.5. Should it hold any pressure after shutting car off, it quite rapidly moves to 0 once shutting down? Going to try running hose and gauge up to windshield if I don’t find anything else wrong with car and see what it’s doing under load.
Running through the gears, you hit 4th and get above 4400-4500 rpm, really starts missing and will even backfire.

That could be your distributor causing the miss-fire at 4500 rpm.

Fuel pump may loose the pressure but shouldn't let the fuel drain back.

My fuel pressure stays around 5 psi and then slowly drops off to zero after shut down, takes about a couple hours. Last year or maybe two years ago it started to drop off like you described. I took the pump apart and found debris under one of the valves. I had filled the tank with a Jerry can and thought that may have put some crap into the fuel pump. Try as I may I could not get it clean enough to hold pressure and I started to have running issues. Dropped the tank this last winter and found the 'sock' over the intake of the fuel pick-up was disintegrating and plugging things in the pump. I installed a 1/2" open end pick-up/sender.

I always chucked the filter in the carb inlet of Quadrajets and installed an inline filter. The plastic ones aren't pretty but you can see if there's dirt in them.

Mine goes to zero psi within seconds of shutting off, I’ll have to take mine apart and check it out.
I’m scared my cam got chewed up with that plate I found between filter housing and block not allowing enough oil back in, but trying to check everything else first. Ordered a new distributor cap and rotor for the heck of it.

Plate between the filter housing and block????

Was it an adapter plate to rotate the housing for more clearance between the filter and exhaust?
Plate for a remote filter?

Plate for the adapter, but no adapter!😡 Someone took out the adapter but left the plate and two gaskets in for some unknown reason. It is a WQ motor so it came factory with adapter, but when we purchased car it had brand new ceramic Hooker Headers on what was supposedly a fresh rebuild. I can see the Headers are designed to work with the filter housing in normal spot and would not fit with adapter and rotated filter housing, so guessing he yanked the adapter to bolt on Headers, but did not pay much attention to the adapter plate and must not have noticed holes not lining up.

What would you guys check next? Car runs like a top just normal cruising around, and will rev to the moon and back if you want it to while in neutral or holding clutch in and sounds great. Run it through the gears though and 1st is good all the way to Red line, 2nd starts to develop a very slight miss right before you’d want to shift, 3rd the miss gets worse up around 4700 RPM or so and 4th it really starts missing around 4300-4400 and will start backfiring. Definitely gets worse the more load it is under. Changed Distributor Cap, Rotor, Fuel Filter, plugs all look good, and last night through a new fuel pump on, same result? Wondering where a guy should look next?

How old are your plug wires
Check them for cracks and splits look for white spots where they might be rubbing on something this would be spark jumping out of the wire
Sometimes wires will cause a miss under load

X2
Good way to check is open your hood when it's dark out and no lights are on and look for jumping sparks.

No kidding: My parent's house had a pole mounted street light directly across from their driveway. One unusual night the light was out while I was looking under the hood of my '70 Mustang. OMG, the light show that danced across those plug wires! I changed the wires the next day.