Ethan Schaag

I got my XJ about 2 months ago. First thing I did was replace the fuel pump and put new wheels on it. It ran okay for a bit then started turning off at random times. I found the crankshaft position sensor wiring to be the culprit there. Some of the wires were melted and the copper was exposed. Now it has developed a new issue that I'm having trouble diagnosing. It will turn on ok and run fine as long as you don't turn it off. If you turn it off after running for more than a minute it won't turn back over. I've been trying to time the cooldown on it, but so far it looks like it takes over an hour to cooldown from just a minute of driving. Any help diagnosing/fixing this issue would be greatly appreciated.

Thanks for the help

BlueRidgeMark

Let's try to clear something up. You are saying that, after running for a while, it will not turn over, right? That means the starter does not engage and make the engine go round and round? That's what "turn over" means.


OR are you trying to say that the starter engages normally and the engine goes round and round, but the engine won't run?


If it's the latter, test your CPS. Could be your ASD relay, too.

Ethan Schaag

Thanks for the advice. The starter engages normally, the engine just will not run. I tested the CPS as described in the video and no issues there. I checked the ASD and it also appears to be fine. I'm not sure where else to look to find the issue.

vroomvroom

In your description, it says you have a '92. I know I have a '96 and parts and designs changed between years. On my XJ, it would run rough when sitting at idle at operating temperature. If I cut it off, I couldn't get it started. I had to wait until it cooled down to start it again. I checked all the usual suspects like grounds, CPS(Crank), CPS(Cam), etc. For me, it ended up being my fuel pump assembly. 1995? and older use the fuel pump on the side of the tank with the fuel pressure regulator mounted to the fuel rail in the engine bay I believe. For '96, Jeep moved the fuel pressure regulator to the fuel pump assembly, but kept the fuel pump on the side of the tank. For '97 and newer, the fuel pump assembly has the pressure regulator on it but they moved the assembly to the top of the tank. Why am I saying all of this?

Well you explained you replaced the fuel pump on the side of the tank, but have you checked your fuel pressure regulator on the end of the fuel rail? The regulator can cause strange things to happen when it is on its way out.

Ethan Schaag

Thanks so much for all the help. It was the fuel pressure regulator. Hopefully it will last a while now before the next problem.

Rapidrob

In the video, his last check was the Hall-Effect sensor generating an AC voltage when the engine is turned over. His meter shows a .02 VAC at rest ( not unusual ) and when he turns the engine over the meter shows a .01 / .02 VAC generation. He then says you want to see a .05 to 1.0 VAC being generated ( his meter should have shown a .07 to 1.02 VAC gain)
He then says the sensor is good? He never says what the no spark problem is/was.
Is a .02 VAC gain normal for a good running sensor? Or is the computer just looking for pulses?
Unless there is an inverter in the sensor, he should be seeing a DC voltage as the magnet on the flywheel passes the Hall-Effect sensor as the flywheel spins?

lawsoncl

Depends on the year. The renix sensor put out an ac pulse as each tooth goes by, and the voltage increases with rpm. Later years have more electronic in the sensor and put out 0 or 5 volts as the teeth go by. That's why the wiring and connector are more critical on the Renix, and on the Renix a bad CPS usually causes a no-start first as the signal is weakest at crank and idle.

My money says bad crank sensor for the OP. Buy a cheap one and see if it fixes or changes the problem. Just beware the quality of the cheap chinese ones is questionable and its possible get a bad one out of the box.

Rapidrob

Thanks for the clarification.