The background- 1991 XJ 4.0 automatic. I started for work, ran for a minute or two and died, would not restart. The fuses and relays all look good. I no longer hear the fuel pump priming when turning the key, but fuel pump still will pressurize the fuel line when I jump the relay.
Tested for spark, no go. Replaced the CPS with a NTK EH0246. The ignition coil looks to be getting voltage, and I replaced the ignition coil just in case. If I momentarily ground the coil I get spark. It had been suggested to me that only a Mopar CPS will work, but the Jeep dealer says they don't make them anymore and the NTK one seems to have good reviews on here. I'm leaning towards replacing the ecu, but wanted to see what more experienced people think.

 

What do you mean by that?

Unplugging the lead from the coil of the distributor and grounding it?

 

I ran wires to the battery to the coil, if I connect and disconnect the ground the spark tester lights up.

 

Meaning the coil is good.

 

Roger that. My rough understanding makes it seem like the coil isn't triggering. When I check voltage to the coil, when trying to start, it shows right around 12v. Which leads me to suspect the ecu, along with the pump not priming like it usually does. Someone did suggest cranking it over to seem it the tach showed any movement, and it doesn't and they still think the cps could be the culprit. Right now I'm basically throwing parts at it, haha.

 

You could wire up and check for power at the pump, but it seems like a good theory that the cps is not sending a signal, or the signal is too weak for the ecu to read.

 

The ASD relay is a prime suspect. If the ASD relay ain't happy, ain't nobody happy.

 

I just tried replacing the ASD relay with a brand new one, no luck, but that was something I wasn't triple sure that I had checked.

 

You tried replacing it with no luck .As in: didn't manage to change it, or changed with a new one and didn't help?
Just clarifying here.

 

I changed it out with a brand new relay, RY116. I had originally grabbed one to check the fuel pump relay when I didn't hear the pump priming.

 

If you want to know more about diagnosing an issue with the ASD, here a comprehensive trouble shoot thread with CCKen going through it at length. Not saying it is the cause, but it has got some great info at understanding.


https://www.jeepforum.com/forum/f11/...topics/1533211