I have a 1987 XJ with the 4.0. It was running fine until one day it wouldn't start. The CPS tested bad so I replaced it. I found an issue with the distributor cap and replaced the cap, rotor, plugs and wires. After that it would start, run rough for a few seconds and die. I have tested the new CPS and bypassed the CPS connector. I have cleaned the dipstick ground and replaced the chassis ground. I have tested the CTS and MAT. I have swapped out the TPS, IAC, MAP, and Coil/ICM. All the vacuum hoses appear good and I don't hear any leaks. The fuel pressure tested within specs. All this lead me to the ECU. I borrowed an ECU from a 1990 XJ with odd results. With the "new" ECU she fired up and idled nicely, but sputtered when I gave her gas. So I put the "old" ECU in the 1990 and it ran normal. Put the "old" ECU back in my Jeep and it went back to idling like shit. I thoroughly cleaned the C101 connector on the firewall and the ECU connectors under the dash with no change. I have no idea what to do with this thing :dunno: