So I recently purchased a 96 XJ with the 4.0 and after putting in a new Crank Positioning Sensor, plugs, wires, it still wont fire. The previous owner put a new head on the preexisting block after the old head cracked because it over heated and he also did a full cooling system overhaul. The fuel system has pressure, I have compression, and I have spark.

What else could It be? If it is timing, what would I do?

 

When you checked for spark, did you check all 6 plugs? When you checked fuel pressure, did you hook a gauge to it or just press in the shrader valve? When you checked compression, what were the numbers?

 

Yes, checked all six plugs
Just pressed the valve
The previous owner said that they were all the same between the cylinders.

 

The PO of my XJ told me the belt squeal "just needed to belt tightened up".
In reality, it needed the adjuster bolt replaced (because the old one was snapped clean off), a new alternator mounting bolt (the old one was missing and the alternator was out of position) and a new idler pulley and of course, a new belt.
My point - don't trust what the PO says - check it yourself to be sure.


I'd definitely hit Autozone and grab a fuel pressure test gauge and a compression test gauge and check that the fuel pressure and compression are truly in spec.

Also what brand CPS was used? Anything but a Mopar is a crap shoot and can and frequently are bad out of the box. These XJ's are super picky about the CPS.

 

It is a mopar piece. and I will give the gauges a shot.

 

Have you ever seen the engine running?

If not, you might want to consider checking out cruiser54.com for info on checking the distributor is indexed correctly.

 

Did old owner have it running after work was done. Id make sure dist is clocked correctly. You can have spark, fuel and compression all you want but it all has to be timed correctly to run.