fuel pressure regulator?

mine is bad, would this cause intermitin fuel delivery to the motor? and cause it to cut out and die?

How do you know it is bad and what year xj? On my renix jeep it has an inline rising rate fuel pressure regulator that is vacuum operated and when the diaphram on the inside ruptures it will pour straight gas into the intake manifold. Pull the vacuum line off the regulator and if fuel come out your regulator is bad. However, it will not cause intermtent fuel delivery...you will still get a constant flow of fuel, but it will run roughly.

1989 xj 4.0 auto, new distribtor,plugs,wires,coil
ya its bad, but iam haveing alot of trouble with this thing i will be driveing it and it will back fire and die? i cant figure this one out PLEASE HELP!

Check the fuel pressure. Most auto parts stores sell the guages pretty cheap, alternatively you can rent one from them (you pay full price, when you return it you get your money back).

1. Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to test port pressure fitting on fuel rail.
2. Remove vacuum hose from pressure regulator.
3. Start the vehicle.
4. Note gauge reading. With vacuum line disconnected, fuel pressure should be approximately 269 kPa (39 psi)
5. Connect vacuum line to pressure regulator. Note gauge reading. Fuel pressure should be approximately 214 kPa (31 psi) .
6. If fuel pressure is not approximately 55-69 kPa (8-1O psi) higher with vacuum line removed from regulator, inspect pressure regulator vacuum line for leaks, kinks or blockage.