Question for the group:

I have an 88 Cherokee 4.0 which I can't get to start. I put a gauge on the fuel rail and have the needed 38 or so PSI. I seem to be getting spark as my timing light is flashing.

The jeep has been in the garage all winter b/c the water pump came apart in the fall. Little by little, I got it put back together. A month or so ago, the job was done, the jeep fired right up, and I drove it around the block a few times, and i thought I had it all fixed. And then, it hasn't started again since. As mentioned above, it seems to be getting fuel and spark. Any thoughts?

Try spraying starting fluid into the carb and see if it will fire.

Yep. Tried that. Doesn't seem to have any effect. So you would think, oh, okay, it's a spark problem, then. But I seem to be getting spark according to the timing light. It occured to me that there could be some ground problem, such that high voltage is coming from the distributor/coil, but the circuit isn't closed b/c of no ground. But I have the usual ground strap from the head to the firewall and it looks okay. I'm stumped on this one.

Do you know this: these 4.0s have hydrolic lifters I think. If they are not getting oil, would they not open the valves at all or would they still do so? I ask b/c if there spark and fuel, I'm wondering now if the fuel isn't getting into the cyclinders and why that might be.

Given that I tried the starter fluid down the throttle body trick, and nothing happened, I don't necessarily suspect the injectors, but do you know how to test if the injectors are working?

I would try to start it then pull a plug.
Check again for spark on the plug and look for fuel on the plug end.
If there is spark, I would check the other 3 plugs for spark as well.
Could be a plug wire as well.
Just takin stabs at the easy stuff first.