Well, I was all set to swap in a new crank sensor today, but I hesitated as I sat there in the driveway with the wheel off and the impact ready. It just didn't seem right.
So, I decided to try one more diagnostic idea that popped in my head. I pulled the plug for the crank sensor, turned on the key, and tested for the 10v sensor power. And, I got 3-4v from sensor power to sensor ground. Woah. That'* not good. The power to vehicle ground was good, about 10-11v. So it was a problem with the sensor ground.
Then I thought maybe it was the harness was bad, so I probed some wires up by the ICM, and got the same result.
Back to the Haynes wire diagrams I went, trying to figure out what the heck was wrong. The diagrams don't really say how the sensor ground is produced in the ICM (whether it'* just a re-labeled vehicle ground, or comes from the ECM, etc.) It does show a couple of black wires coming off of the ICM, one being to the ECM, the other going to ground. I probed the one that existed, and it was either a bad ground or the ECM.
Somewhere in here, I also unplugged the cam sensor, since that also draws power from the same leads as the crank sensor. There was no change though.
Back in the diagrams though, I see that there'* another ground, just a vehicle-contact ground, apparently where the ICM contacts the bracket. Whipping out the multimeter again, I probed for voltage between the positive battery terminal and the metal base plate of the ICM and got... nothing.
I can't imagine how two metal plates can sit next to each other, held together with 6 tight screws and not make electrical contact even despite some corrosion, but that'* exactly what was going on. I cleaned both surfaces with some emery cloth, sandwiched some steel wool between the two for good measure, put everything back together, cranked her, and she fired. A couple fires later, she was started!
Not for too long though, since I had plug wires against manifolds, and really wanted to get my fuel pressure gauge on there to see where that part of the situation was at.
Once I got everything re-routed and heat-shielded, and the gauge in place, I fired her up again. We have about 25 psi of fuel. Not so good. But that'* better than I thought. Key-on only, I get about 20. So, now we all know that a Vin C will run (albeit not great) on 25 psi of fuel.
I pulled the gauge off, closed the hood, and took her around the block (up to 55 mph). She drove okay... the fuel is definitely an issue yet. Still... she'* ALIVE!
And that'* a definite plus for the resale value.
So the big thing that I want to communicate here, is that if you ever have an ignition problem that you just can't find, clean the surfaces of the ICM and it'* bracket! Such a stupid little problem, but I had half the car apart trying to find it, and nearly installed a $30 part which would have done me no good.
Thanks to all who threw suggestions my way! It really could have been any of those things...