Crank fuse keeps blowing

[DHinckley]

1996 GMC Jimmy Auto 4x4. Wife stranded, towed, system checked, the mechanic thought it was the starter but $91 later turned out to be the 10 amp crank fuse. Problem- it keeps blowing. It seems to help sometimes to turn ignition to accy, put in netraul and then start it. The mechanic insists the electrical system test is ok. Something's not ok. Any suggestions where I might start?

[rlith]

Could be a shorted crank sensor (about 7 o'clock on the timing chain cover) I've seen these go bad and cause similar symptoms. You can try changing that out or at least pulling it and run a continuity test on it with a multimeter...

[94 Jimmy]

What is a Crank Fuse? I've never heard of one, now granted I have a 94 Jimmy with a distributor and a reluctor sensor inside, but I have owned GM cars with crank sensors. These sensors are Hall Effect devices which are essentially solid state magnetic switches. The computer (ECM) sends a current limited 5 volt signal to the sensor which switches it to ground when ever a piston is approaching top dead center. The computer takes this timing pulse and other data and determines when to fire the spark plug.
Your right, the crank sensor is the only sensor that does not provide a "limp home" back up in the computer. When it goes, your (your engine that is) dead.
I don't believe the starter solenoid has a fuse, it has a fusible link instead, the ECM has a fuse perhaps that's what the mechanic is talking about.
I suggest you buy the Haynes Service Manual for you truck; it costs about $20 and is worth every cent. It will explain every sensor and gives a simplified wiring diagram.
Good Luck, see ya
94