I have an '88 XJ 4.0L limited. I was driving in Texas on the highway at about 85 mph. I felt the engine surging slightly and then it suddenly started backfiring and I had to stop. The engine idled fine but would not accelerate past 1300 rpms. When I press the gas it will shake, backfire, and sputter. So far I disconnected the exhaust at the headers to check for plugged muffler etc. I have replaced the coil, plugs, and wires. I have dropped the fuel tank and cleaned it out. I've replaced the fuel sending unit, lines, filter, and injectors. I've replaced the CPS & TPS. I've made the necessary adjustments to these and verified with a meter. I've replaced the timing chain and sprockets. I removed the distributor and found the roll pin that holds the distributor gear in place to be missing. I reinstalled the gear and a new roll pin. I set the engine to compression TDC, set the oil pump to the 11 o'clock position. Installed the distributor and verified it was located at cylinder one post on the cap. Started engine still the same results. Tried moving the distributor one tooth forward and back. No luck. Any ideas? I'm currently in Fort Davis Texas. I need to get this fixed to get back to SC.