Stu 55

1991 xj 4.0
hard start first thing in the morning, Tried key on key off,No sound from pump.
Starts after a couple of tries, Ideas rough for a minute, Then runs fine rest of the day???????

RocketMouse

I'd start by checking the psi you're getting at the fuel rail. There is a test port. Some autoparts stores that have a "loan-a-tool" program might have the kit you'd need to test it with.
Typically you would want to test both at idle and at speed.
Someone can chime in...but if memory serves... think it should be around 45psi I think, but don't quote me.

tjwalker

I agree with Rocket, do some fuel pressure testing. Must be done with a fuel pressure gauge, very easy to do.

Test it cold BEFORE you start it, then watch gauge as the vehicle runs rough as you mentioned, then look at the pressure after it's been running for a bit.

The fuel pressuree spec for your 91 is 31 psi, then pull the vacuum line leading to the fuel pressure regulator and the pressure should jump to around 39 psi. If that vacuum line has raw fuel in it, you need to replace the fuel pressure regulator. Also leave the gauge hooked up and see how fast and how much the fuel pressure bleeds down as vehicle sits not running.

Many parts stores will rent you this tool inexpensively, call around for availability. Good luck and keep us updated!