Fuel Pressure Drop with Engine Rev

Hi can someone tell me what would be approx. normal fuel pressure psi points roughly.

Like let's say you have 39 psi no vacuum. Then wish vacuum hooked up it should drop, to about what??? So when I rev the engine up to let's say 2500rpm what should my fuel pressure change to? Cause mine drop's to about 25 psi.

Have been getting code 96 engine off, but can start the car up fine, drive around the block, seems more sluggish than it should be especially at low rpm, can get it going at about 2500 with a slight bit of poping/firing in the exhaust, kinda feels like it bogs a bit, get's kinda like jumpy, not sure the right word, but say when accelerating kinda does the thing where its trying but isn't really smooth kinda struggles but does seem to manage when up there a bit. Was getting to lean then to rich codes, especially when I played with the regulator. Codes I have seen are engine off 96, first engine on 41 and 91, switched both o2's and got just 41. Have 4 o2's in total so can switch through them to find 2 good ones. Anyways after swapping through a bunch of o2's and still getting 91, thought I would up the fuel pressure a bit. Got code 92. But with very slight psi adjustments like 2psi here or there.

So tommorrow I am going to swap my stock fuel pump out for a 190 lph fuel pump, swap the fuel filter. Then will jumper the fuel test circuit key on engine off to get 39 psi with no vacuum. Then I will check with the engine running vacuum off that I am maintaining 39 psi. Will shut it off and reconnect vacuum. Dump engine running codes, take it for a spin, then check error codes. Then if I get 41 or 91, I will swap whatever code side 41right 91left o2 sensor out, dump codes again and take it for another spin. If I come back and still have error codes I am completely lost. Other last thing I will try, and if I am getting engine lean or rich, after all the above is to re-adjust the fuel pressure regulator by approx. 2psi in the opposite direction of the error code from my starting point. Eg. if I get 92, to rich I will lean it out by dropping my fuel pressure to 37psi., and if I get another to lean, I will bump my fuel pressure up to 41 psi. Other than this I am absolutely lost in every way!

If you think I am on the right path with swapping out the fuel pump and fuel filter than I hope your right! But if after all of the above, if there is anything you guys can do to help me that would be great! Because if this doesn't work I really don't know what else I can try! Thanks guys!!!!!

I know it does seem like a pain to have to drop the gas tank, but I do have this 190lph intank fuel pump that I bought thinking I may need it. But I agree it would be nice to just be able to change the fuel filter which I haven't ever changed. But thinking I am gonna bight the bullet tomorrow while on holidays and just get it done!

I does make sense to me that you would loose some psi as the pressure is probably relieved because the engine is using the fuel that's in the rail, so I assume why a slight drop is normal. But like a 15psi drop probably isn't normal. So thinking the fuel pump just needs to be able to keep up.

So here's an update:

I have the gas tank out, which wasn't too bad at all, the filter looks pretty rusty, wouldn't surprise me if it was the original one. So I got it out, used a scrapper to get away as must loose rust under there and gave it a good paint while I was at it. So got the tank off and capped everything off, gave it a power wash. There is a hole in the top of the tank, really rusty.

So luckily I have two spare tanks in the shed, one from a 83 gt vert, and the other from a 6 banger vert also 83 that we used to have. Only problem is it doesn't have the fuel gauge sender unit for the fuel gauge. But the tank is mint. So I think for now I am going to get it up there and just put fuel in often. Will kinda suck for a long trip.

Not sure what else to do. Any suggestions?

So once I actually got the units out, now understand why my gauge wasn't 100 percent! The float was there but broken and kinda dangling.

So with my 88 tank on the upper part there is the fuel pump and lower down in the middle is the fuel level sender.

On the 83 tank there is no hole in the middle where my 88 tank sender is. It uses the hole where the fuel pump goes on my 88 as the sender and must have some sort of mechanical or external fuel pump.

So what I did is gave the tank from the 83 that is in really great shape a good paint with a black rust paint, and am letting it dry over night, then I am gonna figure out a way to use the float if possible on the bracket that holds my new fuel pump. I'm sure this could work some how.

I would throw on some pics, but for some reason my account on here can't seem to handle pic attachments. Like my allowable storage is full. Guess I could delete some.

I will take a few later and try to get them on.

So it was a real pain in the a**! But I managed to get the current bracket modified so I can use the same hole for the old fuel level sensor. Cut my fingers up pretty good, but got it done! So its not a stock fuel pump its the 190lph unit which I think should be just fine for 30lb injectors running not at full duty.

So I have everything wired up and all lines hooked up including new fuel filter. Going out for dinner but when I get back am hoisting it back up and installing the vacuum line. Then I should be good to go.

So I will let you guys know tonight if I am still getting error codes.

Am going to cross my fingers!