Nissan Repair: 97 Nissan Altima, nissan altima, oil lines

Question
All gas lines, oil lines, etc... are good. No dents in the oil pan. It was a relatively light bump. Anyway, "knocking" noise is coming from the starter. The slight jolt must have done something to it. Everytime I turn the car over it grinds something horrible. After not being able to start it I went out the following morning, turned it over, (grinding noise was still there) but it started up and ran like a champ. I drove it for about 5 miles, parked it, came back 2 hrs later and it would turn over(grinding noise still there)but wouldn't start again. We tried push starting it and still nothing. I pulled the gas line off the fuel filter and turned the car to accessory. The gas seems to pumping out pretty hard so the fuel pump seems to work. I pulled a spark plug off and put a screwdriver up inside to check the spark and found that it would spark every 4th revolution or so. This seems a little odd to me. Shouldn't it spark every revolution. The spark seemed a little weak also. How can the car run perfectly one time and then not even start the next? This has me baffled. If my relay or pickup were bad would I even get a spark? If so, how can it spark good enough to have the car running fine and then just quit after turning the car off for a few hours?
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Followup To
Question -
Car has been running great for 5 years. Has about 130000 miles. Never have replaced anything but spark plugs (2 years ago)and Fuel filter (2 years ago). I Hit a small pothole and car shut down. Wouldn't start for 5 hrs. Tried again and started but idled erraticly. I stepped on the gas pedal and it idled fine at high rpm but when off the pedal seems to miss and idles erradically.(I never put it in drive) 2 hrs after doing this I tried starting it again and it wouldn't start so I pushed down on the pedal to give it some gas and turned it over again. Still wouldn't start and was then making a knocking noise as it turned over. Any ideas? Big fan by the way, you really know your stuff.
Answer -
OK,lets check the basics. The engine has oil in it and the oil pan was not dented when it went through the pothole?

Due to the year of the car I would look at the intake hose and see if it was damaged, cracked, and allowing unmetered air to enter the intake. Since we are talking front wheel drive and year the motor mounts could be loose enough to allow the hose to stretch and crack ad that would cause the condition.

The knocking is probably the engine having too much fuel due to the cranking at wide open throttle. Fuel injected engines freak out when you attempt to start them off idle. However, I would have done the same thing you did.

Now, if you find nothing with the first two checks you will need to check to see if it is getting gas and spark. Check to see if there is not a crushed fuel line and check to see that the fuel pump is working and you are getting fuel pressure to the rails. Check the spark by getting a paper clip and taking one of the spark plug leads off and inserting the paper clip intothe boot so it is connected to the clip in the spark plug wire. Now, have someone crank then engine while you hold the clip about a quarter of an inch from a metal part on the engine. You should see a nice blue spark. If you do not the coil is not getting current to the plug and you will have a bad coil or pickup. There is the off chance that you could have a fuse or relay loose from the pothole. Nissan does not have an impact kill switch like Ford cars do that I know of. On a Ford Taurus I worked on there was a kid that was driving so hard he set off the impact sensor and the reset button had to be depressed in the trunk. They worked on the car for a couple of days before I found the problem. Well, write me back if you need more help.

Answer
I want to know if you removed the starter to see if there was damage to the flywheel/flexplate?  If you have a solid state ignition without a distributor the pickup could be at the back of the block with magnets on the flywheel/flexplate.  Since you were discussing a knocking noise and noise when you start the truck one or more could be broken off.  If you have a distributor I would check inside the cap to see if there is damage.