85 300SD: cranks, but won't start

Its a stock 5 cyl. 300SD. Has maybe 300K miles...hard to say as the odometer hasn't been working for a long while. It *was* starting up instantly when cranked, 5-10 seconds. Then a couple of days ago, it began to take longer, a few seconds. Then when I drove to work yesterday, I had to crank three long times, then it started. Wasn't sluggish or rough at all when it did finally start, it was as peppy as usual. But when I tried to start it to get home, it would not start at all, no matter how much I cranked it. THe battery is up, there is plenty of cranking speed. But you can crank all day, and it will not start. It does not even try to fire even a litle bit. I thought it had lost prime, so I tried the pump trick more than once. No go, however. The weather is hot now. When it had bad glo-plugs in the winter, it would emit clouds of smoke as I cranked, from the unburned fuel I guess....now there is no smoke at all. If the timing chain has broken, wouldn't the loss of compression show as the starter turning at a much faster speed because of greatly decreased load? THis was how my Volvo 740 was when the timing jumped. It is still turning exactly the same speed with the same sound. I believe there is a vacuum line that has to be switched to enable the car to start, through the key switch. Don't know how to check this, though. I took the hard line to the no 1 injector loose and cranked the engine, and only a very small intmt. spurt of gas came out, even when floored. But shouldn't gas have come gushing out? I have a fuel press gauge somewhere, I guess I could buy some sort of tee and install in the flex line somewhere...but the gauge has a schrader valve, that is the problem. There is a fuel filter on the line right near the pump, but I can't see what is happening with the fuel as it is an opaque one. How should I proceed? For lack of funds I need to repair myself. ANy help greatly appreciated.