This is on a 1998 Cummins 3C engine, 325 HP turbo charged, 8. 1L (I think). I have cun'n' pasted this so it sounds a bit generic. Long read, any (I mean ANY) advise/suggestions welcomed. I ma at wit's end!
Fuel shutoff solenoid suffered a broken mounting bold and dislodged from it's mount last December. This solenoid has dual coils, one which is energized when the key is in the start position is called the opening coil (high current draw). The other is energized anytime the key is in the on position and is called the holding coil (low curent draw) . The plunger is on an adjustable length linkage and is spring loaded to push the fuel valve closed when both coils are deenergized. The sequence of events (as best I understand it) is as follows:
-key to on position, holding coil energizes (but does not have the strength to fully open the fuel valve.
-key to start position, opening coil yanks the fuel valve open and engine starts (key returns to on)
-the solenoid travel must be adjusted so that the opening coil drops out or the solenoid will overheat (it'll be drawing current through both coils). I do not know why this is so designed. Looks like it'd be pretty damned simple to just interrupt the current when the key comes off the start position.
-key off, both coils deenergized and spring pushes fuel valve closed.
My problem has been that when I turn the key off and the engine does not stop I know the frigin solenoid is still energized and it's getting hot. I watched one blow the top off before I could unplug it. Saw two boil the epoxy out and this one today was merely hot enough to blister my arm when I reached to unplug it. Somewhere a contact is remaining closed. I cannot figure out if it's the key contacts or if there is another relay sticking.
Here's the kicker, today after I disconnected the solenoid, I started disconnecting the feed from different relays/contactors. I physically removed from the chassis and electrical system the starter solenoid and the fuel solenoid but the shutoff solenoid I was trying to isolate was still energized. I putzed around scratching my head and cussing electrons for four or five hours and finally just put all the stuff back as-is. Then just for the hell of it, I checked my shutoff solenoid and the sonofabitch was deenergized as it should be! WTF is this!
So, as you can see, this ain't no simple problem. The RV has been to the Cummins service center three times so far and each time they say it's fixed. I have to take it back to Cummins because the warranty requires that they do the work. The solenoid retails for just under $400 and the labor is another $200-$300. The warranty is a very desirable thing!
Anyone with advise about how to isolate this problem, feel free to dump it on me. BTW: the life expectancy of the solenoid in question is 10-15 years and 200,000 miles. My original one lasted 7-years and only failed because the bracket broke. The subsequent units have been cooking off in 2-months and 500-800 miles of use.
I apologize for the length of this but I hope to cut & paste to a RV forum too.
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