I have a 1990 XJ with 320K+ miles on it. I have owned it for 15 years and have taken good care of it. I am having a hard start issue that I have been chasing for six months. When the engine is ice cold it starts right up, but once the engine is hot and sits for more than 15 to 30 minutes it is very hard to start. The engine cranks right up when I leave for work in the morning. It also starts first try if it only sits several minutes when the engine is hot, like when I refuel. But once the hot/warm engine has sat for a while it is very hard to start, even when it has sat for like 10 hours while I am at work. I have replaced every sensor on the engine: MAP, MAT, O2, Coolant temp, knock, throttle position and crankshaft position. I have replaced the idle air control valve, EGR valve, fuel pump, fuel filter, fuel pressure regulator, fuel line to fuel rail O-rings, plugs, plug wires, distributor cap, rotor and ignition coil. I have removed and thoroughly cleaned the throttle body. I have checked all the fuel injectors and even replaced a few. I made sure all the exhaust manifold and intake manifold mounting screws are properly torqued. The cylinder compression and fuel pressure all check good. I do not see any telltale signs of a bad head gasket. I am at my wits end. I cannot figure out why the engine is so hard to start when it is hot/warm. Any suggestions????

 

Not much left other than the cam sensor/pickup or the ignition module.