96 XJ Fuel Pressure Regulator

Hey all,
So I'm traveling from Tennessee back down to Savannah. On the interstate, my 96 Cherokee starts losing power and stumbling every once in a while. A couple of times I thought it was going to completely shut down. I replaced the fuel pump before starting this trip a week ago due to the same issue.
I have my handy fuel pressure gauge with me and when I stopped at a fast station just now I hooked it up. My fuel pressure was dropping off to Zero almost immediately after turning the key off. I did that maybe 2 or 3 tomes with the same result. I drove down the street to another store about 100 yards away and checked it again. This time it bled down to about 20 psi within a minute. I didn't let it sit any longer but I'd be willing to bet it would've went to zero within another minute.

Having said that, I now have two questions:
1. Is this my fuel pressure regulator?
2. Is this the cause of my Jeep cutting out or is there more than likely another issue?

Thanks in advance for any help you can give!

The pressure bleeding off after stopping should only affect your starting. What you want to test is the working pressure while the engine is running both at an idle and at high RPM's. I've taped my fuel pressure gauge to a windshield wiper (careful with the hose) and gone for a drive trying to recreate the problem.

Have you tried to use the key method to see if you have any MIL codes? The last time mine did something similar I had a code 11. Or to be exact a code 12, code 11, code 55. Code 12 and 55 don't mean much.

Something else you should try to keep track of, does it happen at or near a specific RPM? Does it tend to happen on a hot motor (above 180-200 F), a cool motor (around 140-160 F) or on a cold motor. This is sometimes relevant.

I got codes 12, 21, and 55.
This only happens after I've been on the road awhile and its warm. It acts up between 2 and 3k. When I push the throttle a little more it will kick down into passing gear and straighten out. Sometimes it acts like it doesn't want to stay in overdrive or something. I just tested my throttle position sensor and it checked out fine.

I've seen Renix do that when the O2 sensor is on it's last legs. It will chunk, chunk chunk and buck at or near max torque (2400 RPM +/-) on a warm/hot motor, it feels almost like a transmission issue. Max torque is where the best mileage is and the computer wants to run it as lean as possible, with faulty info from the O2 sensor detonation can happen. Could be your issue, I haven't seen it on an OBD 2, though it sure sounds familiar.

May also be your fuel pressure is falling off and running the motor lean.

Code 21 is the O2 sensor on my list.

If I unplug the o2 sensor will it change anything? Will it even run or will it run worse?

The fast loss of pressure is the one-way check valve on the pump. Its there to maintain pressure in the line (prevent the fuel line from draining). In some cases it can cause bogging under acceleration, since the pump has to fight gravity and there can be some pressure fall-off in the line (not enough fuel being fed to the injectors). They are integral with the pump and not serviceable. Looks like the new pump you put in has a defective valve. Bogging could be from this, or could be something else, I'd look to fix the check valve first anyway, hard starts are bad for the starter motor and engine.

After I installed the new pump, it started taking longer to start. So I can see that. Even with the old pump it started right up. But it was having this issue before the new pump.

ehall I definitely agree with you and will get that taken care of asap

Update: my check engine light just illuminated for the first time. It gave the exact same list of codes I posted earlier: 12, 21, and 55

Im new here how do i post pictures through tapatalk app?

nlayne said:

Update: my check engine light just illuminated for the first time. It gave the exact same list of codes I posted earlier: 12, 21, and 55

Click to expand...

http://www.allpar.com/fix/80s-codes.html

12 and 55 are "normal" -- 12 means battery power was lost at some point, 55 means end-of-data

21 indicates that you probably have a defective O2, that could also explain the chugging

The 96 model is unique in that is stores both
OBD I and II codes. If you plug in an OBD II
code reader or scanner, it might give you more
specific codes. The OBD II port is under the dash
to the left of the steering column.

If you have a CEL, there's another problem in addition
to the fuel pump...good possibility it's indeed an
O2 sensor.

Hey guys just thought I'd update y'all. I put in a new O2 sensor and I haven't had anymore issues. I really appreciate the help. Next time any of you are down towards Savannah the beer is on me.

Thank you for posting the resolution.