There's fuel on it?
Check the injector area for fuel - you might want to clean the area, dry it thoroly, and check it at idle as well.
It would help (as usual,) if we knew what year - here's the reason: The RENIX 4.0 (1987-1990) is known for injector leaks at the body seam, and if you do a search here for "Engine Bay Fires" or something similar, you'll find several RENIX burnouts caused by leaking fuel injectors (they sit right over the exhaust.)
The good news is that you can get a set of pulled Ford 5.0 injectors to replace them - just put new orings on them before you put them in. It's about an hour to change all six of them, and you should DEFINITELY not let this go too long (I'd say get it done no later than week's end - sooner, if you can swing it.) The OEMR injectors are spendy (and even the aftermarket ones specified for the 4.0) but the 19#-20# fuel injectors will serve for the XJ - all years. I'd consider 21# injectors a maximum for a stock 4.0, anything larger than that would probably cause you to run rich - or cause the ECM to overcompensate for the oversize injectors.
Oh - the rating in pounds (19#, 20#, 21#) refers to the amount of fuel the injector will deliver at rated pressure (usually about 39#) Too much fuel injector is like overcarburating an engine, too little will restrict power by not allowing enough fuel to be delivered.
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