Chrysler Repair: van will not shut off, combustion chamber, dieseling

Question
Hi, I have a 95 caravan that will not shut off.  Tried replacing the ignition lock and that was not the problem as the van will start but will not turn off.  I do not have any sort of remote starting system.  Please help. Thank You.

Answer
Hi Jeannette.
How have you been shutting it off? I suspect by removing one of the cables from the battery, correct? Or does the engine sort of keep running but not very well and then finally die?
If it runs absolutely normally and you can drive it with the key in the off positon then: It has to be two things that have gotten messed up. First I suspect the autoshutdown relay may be stuck in the closed position, and if you have a voltmeter or glow light you could check that out or simply pull the relay (it is in the power distribution box under the hood in the front right corner of the box). There is also a wire from the ignition switch that should not have voltage when the switch is off: the dark blue wire that provides voltage to fuses 13,14,15,16 when in the RUN position only may be "hot" all the time due to a short circuit or a problem with the ignition switch, though you said you changed that. It provides power to the engine computer out of fuse 16 under the dash so try pulling that fuse to see if that stops the engine when it won't shut off.
If it runs on after shut off, but not really well enough to drive it, then you are dieseling (running withoug a spark) due to some Hot Spots in the combustion chamber and perhaps too rich a mixture, and the autoshutdown relay would also have to be stuck "on" for this to happen. Dieseling can be helped by driving the engine on the highway at a legal limiting speed for maybe 10-20 miles. Or you may have to put some additive in the gas to clean the combustion chamber of the hot spots. If all else fails in might require cleaning the combution chambers manually but the is expensive and a signigicant mechanical take apart.
So let me know some more based upon my observations and questions.
Roland