My 88 2.6l trooper had been idle for a few days. I went to start it and everything is OK for 2-3 sec and it does out all of the sudden, if you try to restart it it does the same thing. I tested the fuel system and it is pumping 40-45psi as specified. Ignition system is in order, I get a spark to all cylinders. There are no fault codes on the ECU.
Any ideas???

It's not out of gas, right? If it were a fuel filter you would have had problems before with it running, but I would check the filter anyway. Mostly I suspect some electrical problem. It would be nice to know if you can keep it running with the throttle.

Hello Keith, It does have gas and I cannot keep it running if I step on the throttle. I just returned from checking it again and two electrical problems appeared. The 12v output from the alternator is dirty (connector near the alternator), so I cleaned it. Now if I start it again, the starter doesn't shut-off, i had to disconnect the negative off the battery. I least now, I suspect that it is a electrical problem. It still has original problem.
Funny thing is this car ran like a champ before it sat idle for 3 days.

i would suggest the fuel pump, i have an 88 LX as well. the previous owner who owned it for 4 yrs told me it was a big issue

Check the ignition switch (where you put the key in). Burned wires? Loose wires down there?

My 88 2.6l trooper had been idle for a few days. I went to start it and everything is OK for 2-3 sec and it does out all of the sudden, if you try to restart it it does the same thing. I tested the fuel system and it is pumping 40-45psi as specified. Ignition system is in order, I get a spark to all cylinders. There are no fault codes on the ECU.
Any ideas???
On my 88 I had a similar problem. turns out there are two fuel relays. One that powers the fuel pump while starting the engine, another that powers the fuel pump after the key is released. Sounds like yours will start fine, but then runs out of fuel as the second relay is not pulling in. The relays are in the fuse box above the drivers side fender, at least on my 88.