What things could cause a 92 xj to not start with good spark and fuel?
 

92 xj laredo with the 4.0 i6

Died while my wife was coming to a stop last week and hasn't started since.

I've replaced the throttle position sensor, crankshaft position sensor, and the cap & rotor.

*A fuel pressure gauge shows a steady 41ish while cranking.
*Holding one of the spark plug wires next to the valve cover while cranking showed blue spark.
*Error codes showing are 12 (Battery or computer recently disconnected) and 24 (Throttle position sensor over 4.96V), but both of those have been showing since I replaced the valve cover gasket and apparently jiggled the wire harness a bit too much, and it was running then.
*Tried cranking it while jiggling the shifter in park and neutral, no change.

I even tried cranking it while some starter fluid and not a single change. It cranks hard and strong but will NOT turn over. I have to jump it now because trying to start it some much has killed the battery, but still, it's strong but just wont turn.

I'd drive it off a cliff if I could get it started. Anyone have any ideas? I am at my wits end here.

Bad Crank Position Sensor and/or cam position sensor.

Just changed the crank sensor, didn't know there was a cam sensor as well. Guess I'll give that a look. I sure wish the damn computer would just say when a sensor goes bad.

Actually, scratch that, I just wish there was a carburetor that was a direct fit for these engines.

The more I think about it, it just doesn't make sense. If I got spark and spray starter fluid in the intake, how can it not start?

It also needs compression, timing, and air.

Open up the oil filler cap and look in the rocker area while it is being cranked to make sure the rockers are moving.

check your firing order. mine was doing a similar thing but would still start, just ran terribly. i know it's kind of stupid but it's worth checking i think

x2also if you replaced cap and rotor and put some wires back wrong that would be bad

The yellow wire connector denotes #1 on the cap. 1-5-3-6-2-4 is the firing order in a clockwise direction.

Just got it started. The cap, rotor, and spark plugs were all just covered in buildup. After replacing them all, it still wouldn't start at all, but we tried cranking the crap out of it for a while and it eventually started up. I think it got super flooded while trying to get it started.

Anyway, it starts fine now, but I notice it is super sensitive to low vacuum. At first it tried to die when we reattached the air tube to the throttle body but just revved the crap out of it and it eventually accepted it. I had to unplug the rear vacuum line on the valve cover to keep it from idling really low. Basically an intentional vacuum leak. It just seems like it's really sensitive to low air\vacuum.

Tomorrow I'm gonna throw my vacuum gauge at it and see if I can figure anything out.

You may have a broken/loose vacuum line somewhere else.