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And, I learned-a-thing in the process. I didn't know that polarity mattered on a magnetic p/u. In fact, I was sure that it didn't matter.
The cam and crank sensors were butt-connector'd by the PO. Car's ran great for the past year like that, but then died suddenly. My FIRST thought was those butt connectors, and I had my son tug on the wires...crank sensor wire pulled right apart. "That's it!"
So we spliced them proper, heat shrink'd them...but still no start.
While splicing them proper, I asked if he'd noticed orientation before tugging...he told me how he thought they had been connected. I told him that it was a magnetic pickup and probably didn't matter, but we moved forward with the splicing based on his recollection of their orientation. Turns out we were both wrong; He was wrong about the orientation of the two wires....I was wrong that it didn't matter. I still don't know WHY it matters....but apparently, it matters.
So the original problem that caused the car to die was the bad/failed/hacked butt-connector joint of the crank sensor wires. Our own story-telling f'ed ourselves, and exacerbated a simple problem.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by Tom400CFI
Me too!
And, I learned-a-thing in the process. I didn't know that polarity mattered on a magnetic p/u. In fact, I was sure that it didn't matter.
While splicing them proper, I asked if he'd noticed orientation before tugging...he told me how he thought they had been connected. I told him that it was a magnetic pickup and probably didn't matter, but we moved forward with the splicing based on his recollection of their orientation. Turns out we were both wrong; He was wrong about the orientation of the two wires....I was wrong that it didn't matter. I still don't know WHY it matters....but apparently, it matters.
So the original problem that caused the car to die was the bad/failed/hacked butt-connector joint of the crank sensor wires. Our own story-telling f'ed ourselves, and exacerbated a simple problem.
Easy to visualize. Most magnetic pickup circuits use the positive to negative signal transition for switching/timing purposes. Just draw an AC signal on a piece of paper, and mark the positive to negative transitions of the signal as it (time) goes left to right. Now, if you swap the wires, the signal will look like you took the paper and looked at the signal from the back side (time t still goes left to right). The signal negative transitions are now a half wavelength (180*) delayed. Not a big deal if it's an input into a rectifier for power supply usage, but a big deal if you're using the signal for timing (crankshaft position) applications.
Another possibility why the wires being reversed caused a no run: it is possible that is a hall-effect sensor. I've got a few of them in the Holley system in the 85. Normally those sensors are three wire: power (5v or 12v), signal out, and ground. It is possible they are using the sensor body as the ground. If the power and signal out are reversed, there will be no signal output.