88 Xj dies when driving

I have a 88 XJ 4.0 that dies and some times back fires thru the exhaust when I am driving down the road. It will restart like normal but will idle at 2500 RPM for roughly 15 seconds and then will settle down and idle correctly. I have replaced the CPS, ballast resistor, Distributor assy. New wires and plugs, cleaned the C101 connector and used electric grease, I have removed and cleaned all ground wires, I have removed and reinstalled all fuses and relays that control ignition or fuel. I have wiggled wires while it's running and could not make it die. I have fuel pressure after it dies. I dont want to start throwing parts at it but I depend on my Jeep this time of year. Thanks for any help. Tracy

Tracy, you have done a good job at addressing the usual suspects.

Backfiring from the exhaust is usually indicative of a RICH fuel/air condition.

So testing of things that would affect the fuel air ratio would make sense.

*Test fuel pressure. Should be 31 psi at idle, then disconnect the vacuum line leading to the fuel pressure regulator (be sure that line is pulling good vacuum and is not WET with fuel!). The pressure should jump up to about 39 psi with that line disconnected.

*Test MAP sensor

*Test the coolant sensor that inputs to the computer (not the one that inputs to the gauge)

*Oxygen sensors have a finite lifespan of between 100k - 150k. Don't be afraid to replace it.

*You mention new wires and plugs. What about distributor cap and rotor and fuel filter.... Finish the tuneup!

Thanks for the help. I have replaced the entire distributor shaft,cap,wires and cam position sensor. The fuel filter is new also. I will be testing the items you mentioned. I have just been stumped it runs great and it's like someone turns the ignition switch off, no missing,bucking nothing just smooth 4.0 power. Also the back fire occurs after the engine has died and I am coasting to the side of the road.Thanks again for the info.

Link to testing some things on the 87-90.

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

backfire in the exhaust after stalling leads me to believe you are losing spark while still firing the injectors (dumping raw fuel into the exhaust where it ignites in the converter)

I'd look at a failing coil, ignition module, or wiring to them. This would kill the engine but allow the ECU to still see a crank sensor and cam sync sensor signal and pulse the injectors.

You could have some kind of intermittent connection in the engine harness/plugs.

Try this to eliminate that possibility:
Systematically go through the engine bay and unplug every electrical connector you see and spray out both halves with a good elictrical contact cleaner. Plug them back together securely.

While you're doing that, take a look at the back of the engine where the injector harness first connects, near #6 cylinder. IIRC, both 87 and 88 were prone to "rub-through" of the harness in that area.