'92 3.0l lebaron: 20 amp fuse 40-41 blows

QuestionEdit

my daughter has a 1992 chrysler lebabaron 3.0 v6 it quite running found fuse for fuel system was biown it is located in the fuse box under the hood i replaced it ran ok she started to leave in it it blew again tried replacing it an blowed as soon as i turned the key on?i unpluged fuel pump an o2 sensor because i was told it was on same fuse tried a new fuse same thing i thinking maybe dead short somewhere not sure where to start.thanks tom

AnswerEdit

Hi Tom, If you mean the 20 amp fuse directly in front of the the a/c clutch relay that has contacts number 40 and 41, then that is the fuse that passes current to both the automatic shut down relay points and the fuel pump relay points on a red/white wire. When those relays close, the fuel pump relay sends the current to the oxygen sensor and the fuel pump on dark green/black wires, and the automatic shutdown relay sends current to spark coil, fuel injectors, and alternator field coils on dark green/orange wires. So you can see there are many possible parts that could be shorting the current to ground from that 40-41 fuse. The fuse blowing as soon as you turn the key to the 'run' position is that the engine controller is programem to activate the asd and fuel pump relays for about 1 second and then shut them off until you move to the 'starter' position of the ignition switch so for that moment all the items I listed are powered up. It will take some detective work because the asd and fuel pump relays will only close when the engine is running (or being cranked by the starter) which of course it won't do when the fuse is blown. So I would be inclined to start at the powered items listed above, themselves, and see if any show a dead short to ground. A resistance of more than 1 ohm will not by itself blow the fuse (0.6 ohms or less will blow it), Check the fine/fragile wires at the oxygen sensor would be my first choice. Then the field coil dark green/orange wire of the alternator. The injectors/fuel pump/spark coil would be the least likely to be shorted to ground but check them nonetheless. There are also a red/white to pin 3 of the engine controller and a dark green/orange to pin 57 of that controller but those are unlikely to be the source of the short unless the wire proper had damaged insulation as was grouning out against nearby metal. Please 'rate' my answer (see below). Thanks, Roland