Having some fuel issues....

So I've been having a fuel delivery issue ever since I started driving my Cherokee. It's a 96 4.0 5spd. It runs fine untill about half throttle, then it just flattens out and doesn't have more power. Sometimes it bogs. I put on a pressure gauge and it was right where it should be at 50psi. Thinking fuel wasn't the issue I changed the rear o2, no change, checked the TPS and MAP and they were fine. I pulled the hood off and hooked the guage up again and drove it around and at more than half throttle the pressure would drop, sometimes down to zero at WOT. So I changed out the pump and regulator and nothing really changed. I bought a second pump and just installed it today and still nothing has changed. Pressure still drops. I checked for kinked fuel lines and they were fine. I also swapped in another set of injectors just to rule those out. I also unplugged the pump and ran it straight to a battery and still same issue. I'm stumped and done know what else to do. Any ideas?

After trying three pumps, you should assume there is something restricting the fuel flow enough to drop the pressure under heavy demand.
Have you tried disconnecting the pump and the fuel rail and blowing compressed air through the line, between the fuel tank and the fuel rail?
The line could have an internal blockage, open just enough for adequate fuel to sustain low RPM operation but starve under heavy demand.

It's the front 02 sensor that controls fuel trim not the rear 02

If when you ran the pump direct off a battery you did a road test and got the same pressure drop?

Does the '96 have a return line back to the tank from the rail, or is it returnless? Wondering if something is causing the fuel to get sent back to the tank instead of to the injectors, but I'll admit I don't know off-hand how that might happen?

Rob Mayercik said:

If when you ran the pump direct off a battery you did a road test and got the same pressure drop?

Does the '96 have a return line back to the tank from the rail, or is it returnless? Wondering if something is causing the fuel to get sent back to the tank instead of to the injectors, but I'll admit I don't know off-hand how that might happen?

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Returnless.

Check your fuel filter too. It should be just ahead of the fuel tank on the driver's side. Remove it (just two rubber lines and a clamp bolt, super easy.) and as stupid as it sounds, try blowing through it. If you can't feel air hitting your hand on the other side, it's probably seen better days and needs replacing.

JeepNoob said:

Returnless.

Check your fuel filter too. It should be just ahead of the fuel tank on the driver's side. Remove it (just two rubber lines and a clamp bolt, super easy.) and as stupid as it sounds, try blowing through it. If you can't feel air hitting your hand on the other side, it's probably seen better days and needs replacing.

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And should have been replaced with the fuel pump

You could also try unplugging the front O2. Likely not it but hey it’s free to try.