I have an 89YJ 5spd that I installed a 4.0L from a 91XJ. I drove it all hunting season this year and it ran fine but after hunting season I let it sit for about a month and half without starting it. I went out and started it after it sat that long and it ran fine for a while but then it started cutting out a little when I would give it gas and it slowly started getting worse and worse.

Now when I start it, it runs rough for about three seconds and dies? I have no clue what is wrong with it, could it be the fuel sat to long and went bad? Could it be the CPS? Could it be the Distributor or oxygen sensor? I need help with this one.

P.S. BigJim that is a monster buck.........

Jose How does it die? Will it restart? How much fuel is really in it?
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

When you let it set, how much fuel was in the tank? Could be water consensation causing the problem.

Another thought, I had a truck that sat for about 6 months. I got it started, but when I tried to drive it, same problem. Stuttered and sputtered. Took the fuel filter out and it was clogged with varnish. Replaced the filter and all was fine.

It sounds like classic symptoms of a bad fuel pump to me. What kind do you have? As noted, could be a clogged filter or other restriction. A quick fuel pressure check (with gauge) would be a good first step to diagnosis. The gas didn't go bad in a couple of months just from sitting. Contamination is another story. It's also unlikely to be a condensation problem unless the tank's been open all that time <img src="/forums/images/graemlins/cheers.gif" alt="" />

Thanks,

The tank is 3/4 full and it will start and run really rough and die and it even back fire once. It does this every time I try to start it now. When I installed the 4.0L I also installed a used 20 Gallon tank with the used fuel pump. The fuel pump has always been really loud and runs continuously? Should it run continuously or should it pressurize and shut down?

Try this... turn the key to the run position and see if the pump runs and then cuts off..it should. Then after cutting it cuts off start it and see if it will now idle..
It could be a coil...or other electric device also.. does it start up right after it stops running?
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

[color:"red"] No, it should not run continuously! [/color] You have a fuel system problem. Probably a bad pump (my bet) but could be other especially since this is a custom setup. Custom or not you need to check for fuel pressure. Now would be a good time to add a gauge to your tool collection. I'll look up the pressure specs for you if you get a gauge.

Thanks,

I took the hose off that supplies gas to the fuel injection rail and turned the key over and it took about a minute for gas to start squirting out? When it did start getting some gas it wasn't a stream of fuel and all the time I was waiting for fuel I could here gurgling like the pump was trying to pickup fuel? Could this just be a clogged fuel filter?

I think the pressure needed for fuel is about 30psi?

Sure it easily be a filter.. And I think there is one in that model of Jeep...unless you have deleted it.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

Fuel pressure for a 91 XJ or YJ 4.0 should be 31 psi with the engine running vacuum hose connected to regulator. With the engine not running or the regulator disconnected the pressure should be 39 psi. that's measured at the test port with the hose connected to the rail. The pump itself should produce at a minimum, 75 psi and may go over 100 psi. The manual says if the flow is blocked the pump should reach 75psi within 2 seconds. Do not run it blocked for over 3 seconds. I doubt if it's just a clogged filter but I guess it's possible. It sure is easier to change a filter than a fuel pump. <img src="/forums/images/graemlins/cheers.gif" alt="" />