4.0 on 33's struggles to go past 60 mph

Sensei said:
I did find a second o2 sensor, immediately after the cat. So my common sense tells me that the computer is essentially measuring the “effectiveness” of my cat? I don’t really understand why I’d need an o2 sensor right before and then right after otherwise, but I’m no car engineer.
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When the OBD2 law past one of the requirements was that if any system produced 150% of allowable emissions the CEL must turn on. At that point the manufacturers started running active tests on systems vs looking at individual components. While driving at a steady speed the ECM May look at the cat efficiency by duty cycling the injectors and comparing the upstream vs downstream sensors to check how well the cat is working. These are “system monitors “ if you have emissions testing one of the things they will do is test to see if the monitors have cleared before running on a Dyno. When my truck was newer they would just plug in the scanner and see if all the monitors are cleared, if they are my vehicle would pass. No dyno testing required. Still cost the same though.
 
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Alright so I tried testing fuel pressure at the rail today. Can't seem to pull a reading from the rail when connecting my tool with key turn or vehicle running. No fuel leaks out when attaching the tool aswell. This leads me to believe the connector im using isn't right for the "Schrader" fitting on the fuel rail. This is what my setup looks like.

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I only tried hand tightening the connection, maybe I should grab some pliers and try to screw it on harder so I can engage the pin?
 
Trevlaw said:
Buy an O2 sensor plug from an exhaust shop. Drill and tap the center of it for 1/8"npt threads. Attach an air pressure gauge, 0-30 psi or similar, to the plug via a hose and some npt barb fittings. Unscrew upstream O2 sensor and replace it with the gauge. Start the engine and see what kind of psi you have at idle and at around 3k rpm. Try to be quick with the testing, otherwise you might melt the hose.

I have the exact same drivetrain, tire size and gearing as you. Mine was topped out at 70mph with the foot on the floor. I had about 30psi of back pressure at 3000 rpm. After gutting the cats it went down to 2-5 psi and driving it after it ran like a raped ape, 100mph is no issue now.
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On the way to autozone to buy a different guage to test my fuel pressure, I think I experienced this "raped ape" feeling in my jeep for the first time ever. My jeep was absolutely hauling ass, easily pulling past the 60s into the 70s with very minimal effort put into the accelerator. Never have I experienced power in my jeep like this before. But then all of a sudden it died, while my foot was on the accelerator. Had to crank it about 5-6 times waiting a couple minutes in between before it started again. I then arrived to autozone, bought a new gauge, and tested my pressure right there in the lot. Check this out. Can't hold residual pressure, and pressure seems too low in general. Thoughts?


 
Another interesting thing I found while digging under the jeep. Looks like the fuel pump wiring has chaffed a little bit on the plastic protective loom. I wonder if when I hit a bump, its possible for these wire to short on eachother, and cut my fuel supply, thus shutting the jeep off. Is such a thing possible?

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Sensei said:
On my second video, does the running pressure seem low?
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I believe the spec is 49 +/-5 psi. So you're at the low end of spec. It may be a good idea to get a longer hose for the fuel pressure tester, so you can hold the gauge with the window rolled down and see what kind of pressure you have while actually driving. It should remain the same at idle and driving, so if you see a dip when you really get on it you might consider replacing the pump.

I would probably start by just repairing that worn section of wire and see if that changes anything since it's the easiest/cheapest option and since it seemed to work better for that one drive before it died.
 
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The fact that it won't hold pressure after priming is enough to condemn the pump by itself, unless you have reason to believe the system is bleeding down due to a stuck-open injector.
 
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Yeah, I'd replace that with a pigtail for sure.

It's possible that neither of these are what is specifically causing the OP's lack of power, but they're both obvious problems that need to be corrected either way.
 
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I've helped isolate the frayed wires with additional electrical tape. Jeep was driving pretty good again today. I've also ordered the Delphi pump, and a Mopar crank position sensor to replace.

Anyone ever have an issue in the morning when shifting from R to D sometimes, the jeep just lurches forward, groans, and dies. Other times it will lurch and remain on, but if I tap the gas the trans wont engage until I rev it a couple more times. I think this is an unrelated problem, but it does cause the jeep to lock up and die sometimes. The behavior is not exactly 1:1 with the dying behavior I experience while driving, but it is still troublesome.
 
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