This one has stumped me for years. I recently started listening to Car Talk via podcast, and I figured I’d give it a shot here in the forums while the brothers are on summer break. I’ve tried googling for this as well as asking mechanics and dealers to no avail. Here goes, wish me luck!
I have driven 3 different Nissan Sentras over the years. My most recent one is a 2003 2.5L LE. Prior to that was a 1998 GXE. Prior to that was a 1991 basic sedan (no frills). In all three of these cars, the engine would periodically not start. The battery would be fine; you could get accessory functionality. The engine would simply not start. No turn over, no crank, nothing.
On the 1998 and 2003, I did some experimenting over time, and I eventually narrowed it down to the following conditions that seem to correlate with the failure to start:
* gas tank is at or near 1/4 tank
* last run of the car was for a short period of time (e.g., to move the car from the garage to driveway)
I also have found two methods of getting the car going (via trial & error as well as various advice):
* floor the gas (flood the engine) while starting the car
* bang on the gas tank with a rubber mallot while turning the ignition
(that last one was the advice of a mechanic who claimed to see this problem all the time)
With this info and this long period of experimentation, I pretty much have the issue in a reproducible state. That is, I can make my 2003 sentra fail to start by running it less than a few minutes when the gas is at 1/4 tank or less. I can also avoid this problem altogether by simply never running the engine for less than about 5 minutes.
Anyways, since I can avoid the problem, it’s not really causing issues for me anymore, but I’m incredibly curious as to the root cause. Given that I’ve experienced it on 3 different Sentras but cannot reproduce it on any non-Nissan car, I’m inclined to think it’s a Nissan specific issue. When I’ve taken the issue to the dealers, they’ve entertained me with a number of different stories. They’ve blamed the gas (ethanol content, octane), the weather, the battery, the oil, vapor lock…but basically, they’ve never owned up to anything that requires fixing. The general dealer consensus seems to be that it’s just the way cars (read: Nissan cars) work, that you can’t run the engine for a short period of time. My shock and disbelief at this statement never seems to sway them. 
The non-dealer mechanics I’ve taken it to have agreed with my experience, in that they generally seem to have heard of it happening on other Nissans, but to date, none of them have had any explanation for it.
Any thoughts?
I don’t have a clue what the gas tank level would have to do with the starter not cranking, unless there is some kind of interlock between the fuel pump (or the fuel pressure) and the starter. I realy don’t have any idea.
I don’t see any correlation between a starter motor not cranking the engine and the gasoline level in the tank.
I could see vibrations in the car caused by getting in and out of the car, opening the hood, pounding on the gas tank, etc. having an affect on a shaky neutral safety switch.
Surely someone through all of this could spend 5 minutes tracing this out when it will not start.
Darn. Well, it was worth a try at least. Thanks for thinking about it.
One of the dealers’ shops blamed vapor lock. He said that the fuel pump gets vapor and never gets fuel when the engine is run on low fuel for a short period, and because of that, the onboard computer locks up the car, thinking that you’re out of gas. That’s why flooding the engine works to start it up. The dealer-mechanic seemed to think that was resetting the onboard computer, letting it know there was actually fuel or something.
You cannot flood a fuel injected engine by holding the gas pedal down. The fuel management computer does the opposite. If you hold the pedal fully down while cranking, this sends a message to the computer to shut down the injectors completely. It’s used to counteract a flooded engine.
The other effect of doing this is that more air can enter the engine since the throttle plate is fully open. This helps even more for flooding problems.
A failing fuel pump may not develop full fuel pressure causing a poor spray pattern out of the injectors. Kinda like your garden hose nozzle when partly opened. This can cause a flooding condition.
A failing fuel pump can lock up. Banging the underside of the tank can help it to get unstuck.
None of these conditions will inhibit the starter motor. Perhaps you have more than one problem. The starter relay may be failing too.
I’m a bit confused here, when you say “no turn over, no crank, nothing” do yo mean the starter is not engaging, there is no sound at all? Not even a click?
You say this happens after you use it only briefly, but does the failure to restart occur within a short time frame after shutdown or would it fail to start even the next day?
Nothing in the gas pedal position or banging on the fuel tank or fuel level has anything to do with the starter motor operation. If the starter is working but the engine refuses to start up and run, then that is a different situation and there are explanations.