Have a 97 jeep grand Cherokee with 5.2. Bought it with blown head which led to deeper mechanical issues. Put it all back together and it ran great but was using a little coolant. Tore it back down, found issue in gasket, and put it back together. It fired right up again and ran for a bit. I shut it down to tighten up some exhaust leaks at manifold and started it up again. Everything was good. I shut it down and now I have no spark. I replaced camshaft position sensor, coil, and crankshaft position sensor. Nothing. Tested power going to coil as well as Auto Shutoff relay. The instant the key was turned on the power to coil would jump to 12v and almost instantly drop to 0v. The Relay tested good. The PCM is all I know to do at this point, but would be curious to know if there were other options. Thanks

 

This has nothing to do with your spark issue, but did you use thread sealer on head bolt #7? That's the one in front on the driver's side. It's threaded directly into the water jacket and will allow coolant to seep up the threads and into the manifold stud threads. The exhaust is hot enough for it to boil off and it only leaves a flaky residue on the manifold nut.

Check for power on the injectors. If the same thing happens (coming on at 12 volts then dropping to 0 volts), I suspect the ASD relay is dropping out.

 

Thanks for the input. I will check the injectors in the morning. I'm also going to replace the auto shutoff relay even though it tests okay.

 

Forget what I said about the head bolt! I was talking about the 4.0! My bad.

 

Sounds like a very bad connection, possibly. basics to start with. Check battery cables and ground, connections at the starter solenoid, ..do you hear the fuel pump run for 2 or 3 seconds? Do the headlights come on? Does the engine crank?