Im working on a 4.6 for my 64 f100. I stripped all the in cab wiring and test started up the engine. Then worked through the wiring under the hood. Everything seems fine and no concerning codes....except now the computer isnt seeing a signal from the spark control.

I checked my crank position sensor once with an ohm meter and it was good. But during all this I checked it again and it was blown. Ive replaced the edis and the cranks sensor with a new one. I checked the new one before install and it had resistance. Not after hook up.

Im starting my research on what could cause it to blow that sensor and wondered if anyone had ideas. Ive got it setting in the original car frame and am wondering if how I have it grounded could cause this. One of the originally grounded to the car body grounds I now have grounded to the car battery.

Anyway, if you want to see the build thread or have any ideas I sure would appreciate it.

https://www.ford-trucks.com/forums/1...o-64-f100.html

 

I'm going out on a limb and suggest checking most any sensor with an Ohm meter doesn't produce all that reliable or accurate results. Further extending myself I wonder if running DC current through the wrong connections couldn't be an issue all by itself?

OTOH I have to think IF the crank sensor is repeatedly blowing there is a wiring issue, possibly battery voltage/current being fed to the wrong terminals.

Double and triple check your wiring according to the donor engine's year EVTM to make sure everything is electrically routed as originally intended.

HTH

 

Thanks for the reply.

Well, i figured out i missed a "power ground" that goes to the ignition control module. It ran all the way through the engine and came out in the set of wires i removed along the front of the car.

It's attributes were:
- when connected to ground it made the test light come on with the test light in series (in line) with the ground wire.
- when not grounded it apparently causes the ignition control module to put out a current detectable with a test light on both terminals of the crankshaft sensor. Most likely this blew my sensor.
- when grounded there is no longer a detectable current (test light doesnt light up) at the crank sensor in ignition on mode. I assume this is as it should be as the sensor creates its own signal and sends it to the ignition control module, there shouldnt be a signal or current going to the sensor (i would think).

I grounded the wire (not to battery ground) and it stopped the code for "no signal from ignition module. It also stopped the wires going to the crank sensor from showing a voltage. Im not sure if this is a self protection design or what causes it. Ill have to do more research.

Im not completely sure about all this right now but it seems to be a move in the right direction. Ive verified it is the power ground to the ign cont mod by checking with an ohm meter, color, and the wiring book and it was not grounded while i was messing up crank sensors. At this point im not getting it to start but i think i need to replace the crank sensor now that its not getting power sent to it, as it shouldnt be. I did have someone try to start the engine while i checked for voltage (should be fluctuating) from the crank sensor (after resolving the other problems) and it was not giving any voltage. It should be making its own and sending it to the ignition control module while the crank is turning. Im sure the sensor got fried while the ground to the ignition control module was not grounded. Ill do some more research, replace the sensor, and try again.

 

this is a two wire cranks sensor, by the way....i believe 3 wire ones do get power sent to them.