I have a 91 XJ 4.0L fuel injected 6Cyl. manual trans. I replaced my fuel pump and some one here told me that the pressure at the bleeder valve on the fuel rail should be about 49psi. is that true, when I have the key on I hear the fuel pump pump up. it stops and when I open the bleeder valve and poke something into it to open the valve the fuel sort of just runs out. I would think that with 49psi, it would squirt out there like no tomorrow....what would cause it to flow out and not have the power 49psi would have ?

 

First off, you have been misinformed. 49 psi is what later model 4.0 engines have for a fuel pressure spec. The fuel pressure for a 91 is 31 psi.

The only really accurate way of determining fuel pressure is with a fuel pressure gauge installed on that valve. But with good fuel pressure, it should not just dribble out of the schrader valve.

Primary suspects are a prematurely failing fuel pump (especially if it's an Airtex) and a clogged fuel filter. When was the last time the fuel filter was replaced? If it's been a while or you have no idea, get a new one in there. It's a 15 minute job for a 91; located right alongside the frame rail on the driver's side.

 

Just to back up a little.....does the Jeep run with the new fuel pump or just crank over?

You can "rent" a fuel pressure gauge from most of the big name parts stores with tool loaner programs. I borrowed one from O Reilly's recently.

If the pressure is low with the new pump then I agree with TJ about the fuel filter..... or a defective pump.

 

thanks guys for the insite, and you were correct. even though the fuel filter was new, I couldn't even blow through it, so I got another and all is well. the motor starts right up and runs good. it just goes to show ya, that even if you replace something with a new one, that new item can still be bad. I should have tried to blow through it before I installed it. all is good now and thanks again.

 

Glad it was a simple fix.

Odd to get a bad "new" fuel filter though. If this next one clogs up quickly, I'd be concerned that you have some material that is responsible for this in your gas tank.