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A knock sensor has nothing to do with crankshaft position, those are two different sensors. I've yet to see a Volvo that would not start due to a bad knock sensor. I don't think that any "decent enough" car would decide not to start because of a bad knock sensor. In fact, I don't think most ECUs make any use of knock sensor input during cranking and startup. It wouldn't make too much sense.
Now, with a bad crank sensor you can't start the engine as there will be no spark. I doubt how one could get a spark w/o an operational crank sensor. Maybe the computer has some "educated guess" limp home mode that would not be enough to start it... I doubt it. It needs to have some sort of crank position information just to time the spark properly. If there's no crank position input, the computer cannot know when to fire the spark and when to fire injectors (in most cases). And you don't really want firing sparks at random points in time. It can have some nasty consequences. Your intake definitely wouldn't agree more, it being mostly plastic and the burning mixture ejected via the open intake valve being quite hot.
If one has a decent spark I doubt that the crank sensor would be dead. Maybe dying but not dead.
If you have fuel *and* spark I'd suspect (roughly in that order): fouled/flooded plugs, disconnected plugs somewhere in the wiring harness, plugged exhaust (usually the CAT converter or a "funny" kid stuck a potato up your exhaust pipe), a bad manifold air pressure (MAP) or air mass (AMM) sensor, maybe also bad TPS. That's all assuming that the engine is mechanically sound, i.e. that the hydraulic valve lifters didn't overfill and that the valve is right.
If the fuel is sprayed out of injectors and there's spark the car should start. It may run crappily due to bad fuel pressure (worn pump, bad FPR), dead/slow O2 sensor, exhaust misperformance (plugged cat or resonance due to a hole) or a host of other things, but it should start.
I've never had a problem with e.g. my 93 '940 starting up, even at -30F. That's fifferent than an 850, sure, don't know if they have such problems. I've had "slow starts" due to a leaking check valve in the fuel pump, but that's not really a no-start. You turn the key to position II a couple of times, waiting every time till the fuel pump stops, and then it starts right up.
Cheers, Kuba Ober
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