'95 GC 4.0 mystery problem from hell!
 

Heres the story, 1st week of July my JGC just died w/o warning on the hiway.

The engine will rotate fine, but will not turn over at all.

Items replaced:
Crank Sensor
Cam Sensor
Cap, Rotor, Wires


Items known to be OK:
Plugs
Coil
Fuel Pressure
ASD Relay
Fuel Pump relay


The Problems:
The injectors are all getting 7.5v when they should have 12v (keyON)

If I unplug the coil, and then plug it right back in... and then check the injectors again, they only read .03v until I turn the key off. When I turn the key on again and check them, they show 7.5v again. I have 12v going to the coil btw.

At the PDC if I remove the ASD Relay and put the voltmeter in the sockets, I get 12v on three of the sockets, while I get 7.5 on another. As far as I know, there is supposed to be 12v on two sockets only. BTW, if I unplug/replug the coil, the socket that read 7.5v will then read .03 same as it does @ the injectors.

When I remove the FP relay, and the ASD relay... the two sockets that showed battery voltage as mentioned above that were not supposed to have voltage... do not show voltage anymore.

If I disconnect the harness from the Alternator, the Injectors will show 10.4v...


WTF is going on!

1995 Grand Cherokee Limited 4x4/4.0/AT 165k mi

I am also getting a code 12... there may have been other codes but they were likely erased when I disconnected the battery to inspect the terminals right after it died.

rotate/turn over, same thing.

I believe that code 12 just means that the battery has been disconnected in the last 50 key turns or something like that.

You know what I mean....


Well everywhere I have seen it listed, it says that battery power has been disconnected from the PCM in the last 50 cycles.

Is that saying that power was cut from the PCM itself, or that the battery has been disconnected.

I assumed it meant the battery, but in looking at the kind of issues Im having... it could be that the PCM suffered a power loss separate from simply taking the terminals off the battery.

That code 12 is from you disconnecting the battery cables. Computer codes

is your distributor firing?

Sorry. Spark from the coil wire or plug wires?

I am getting spark from the coil and at the plugs... the spark @ the plugs doesnt seem as hot as Id like to see, but its there.

also, the rotor is turning too

It was the ignition coil...

Yeah I know.


The crazy thing is that I had tested it, and it passed. Just to be sure I took it to Autozone and had them test it too, it passed again with the same readings as a new one they took from the shelf?????????????/

So I dont know how, or why... but its running again!

But, its got to go. I dont trust it, its betrayed me. Im putting it on Craigslist.