Hi all! Some friends and I share a 91 Nissan pickup that we use mainly for hauling stuff short distances (loads of mulch, helping people move, etc.). Recently we got the fuel pump and tank replaced after it was having some fuel line issues (not starting at all). After we got the work done, the truck ran fine for 5 miles or so, and then broke down again with exactly the same issue – it would crank but not turn over, as if it was not getting any gas. Sometimes it would start and run for a few seconds but then die out. Our mechanic said that maybe the the junkyard tank they had originally installed was dirty and there was trash clogging the fuel line, and they found a new tank and replaced it for us at no charge.
Now our truck will run great for maybe 20 or 30 miles, and then die out again with exactly the same fuel line issues. The weird thing is after it rests for a while (or maybe after it is moved/towed), it starts right up again and will continue to run for a bit, and then die. Sometimes we can even get it to start again after waiting just 10 or 20 minutes, and then sometimes it continues to crank but not turn over for a few weeks until it starts running again. Last time we got it towed to the mechanic it perked right up as soon as they got it in and worked, and I felt kinda stupid for having them tow it in the first place.
Any ideas of what could be causing this intermittent problem???
The problem might be caused by a defective Crankshaft Position sensor.
http://www.rockauto.com/catalog/moreinfo.php?pk=40296&cc=1210981
The computer takes the signal from this sensor to determine if the engine is rotating. And as long as the computer see’s that the engine is rotating the computer runs the fuel pump, fuel injectors, and the ignition system. But if the computer loses the signal from this sensor and thinks the engine is no longer rotating, the computer see’s no reason to run the fuel pump, injectors, and the ignition system. So the engine stalls and won’t restart.
Even though it’s called the Crankshaft Position sensor, it’s actually located in the distributor.
Tester
Are you sure it’s fuel? Are you sure the pressure is dying? Ignition problems, like a heat-soaked coil or a bad sensor @Tester mentioned also needs to be checked.
The trouble might be with the power wiring for the fuel pump. Like a bad fuel pump relay or bad connection possibly. It is pretty easy to verify there is a problem with the fuel system by spraying a small amount of starter fluid into the air intake when the trouble happens. If the engine responds to that you have proven the fault. If the engine doesn’t fire up then there may be another issue like the previous posters mentioned. The crank sensor is a very likely culprit in that case.
A fuel pressure test is probably in order. It may be there is dirt in the tank clogging the fuel filter (or inlet sock to the pump), and over time it clears up enough to start. But when you run the truck a while, the dirt in the tank jiggles around enough to get sucked into the pump then it re-clogs the filter. The fuel pressure test would tell you for certain if the fuel filter is semi-clogged or not. What you do next depends on the results of the fuel pressure test. For it to be diagnostic, you have to perform the test when this no-start problem is occurring.
As mentioned above, it could be non-fuel related too. Testing for spark at a spark plug is another test to consider doing.
The next time it dies, immediatly crank it and check for spartk at a spark plug. If you don’t know haw to do that get a spark plug tester ( you can get one at Harbor Freight for about 5 bucks ). You take a wire off whichever plug is easiest to get to and plug into the tester, then plug the tester onto the plug.
I think you will find no spark when the truck won’t start.
Thanks everybody for the ideas! I went in this morning to check the spark & the crank angle sensor but just my luck the truck decided to run fine today. So I can’t diagnose the problem yet 
Maybe it knows you are on to it, and just to spite you, it will start fine forever more. Don’t let it know, but you win! 