ArcticMania

I have a 1990 XJ, 4.0 Renix engine. This last summer after going through deep mud up to the rear windows it started running rough and having trouble stalling once it warmed up. It would stay running at high speeds but not trail speeds. We replaced the TPS yesterday. It didn't change anything. They gave us the wrong Coolant Temperature Sensor yesterday and got the right one today(the old one was definately bad). After changing it, it ran fine for a while then suddenly ran extremely rich with black exhaust and died then would not restart until it cooled down. We changed the rotor, cap, wires, and plugs along with the fuel filter while it cooled down since these needed to be done anyways. It continued to run very rich and die. We traced down several melted wires to the Coolant Temperature Sensor, O2 Sensor, and Knock Sensor. This may be why it suddenly died (from movement & shorting out) but the wires had been melted for a while. After fixing the wiring it continued to run very rich with black exhaust and die and now it won't even start after the initial second or two of running. We think it is either the O2 sensor or the ECM. We'll try that later. There does not appear to be any vacuum issues and the MAP sensor seems to be working.

Anyone have any other ideas?

ArcticMania

any help?

bkdrocks

I have similar issues with an 1988 MJ??? Let me know what you find PLEASE!!!!!

ArcticMania

We tested the MAP and it definately is good. Now we need to test the fuel pressure.

bkdrocks

I didnt see where you had checked fuel pressure,That turned out to be my problem.The line from the pickup tube to pump had slipped off and was just sitting on the end of the tube,pushing fuel to the fuel rail but not building enough pressure.It had 9 pounds and needed 31-39.
Hope this helps

ArcticMania

We tested the fuel pressure. It was consistently 40psi. I found an ECM from a 1989 XJ. It was a little different with two ports rather than just one. We tried it and it would start but not continue to run. I need the correct ECM. Does anyone have an extra ECM?

ArcticMania

It was the ECM. The TCM is behind the dash on the passenger side and the ECM is on the driver side. Soon as we switched the ECM it ran great. The larger plug on the ECM is the same as the one on the TCM.

ECM on the left and TCM on the right.