Is Vapor Lock Extinct?

nissan
xterra

#1

After I fill my 2004 Xterra up with gas or even if I just get a half of a tank, the day after it will not start. I have full electrical power on the dash board. There is no clicking or stuttering, I turn the key and nothing happens. Sometimes when I take the gas cap off and put it back on it will then start but sometimes this will not help either. I never know when it will happen but I know it will happen at least once sometime shortly after I have put gas in. Oh, my Xterra has 160,000 miles and I have never had any problems until now. I have been diligente on scheduled upkeep and maintenance.


#2

If you turn the key and nothing happens, you don’t have vapor lock. Vapor lock is a bubble in the fuel line due to the fuel boiling. The starter will crank the engine, but the fuel won’t reach the cylinders and the car won’t start. The last car I had that vapor locked was a carbureted 1983 Mercury not so grand Marquis.


#3

What you describe does not sound like vapor lock, it sounds more like a failed starter solenoid, ( I know, usually it is the high amp circuit in a solenoid that fails, but sometimes the pull in coil will fail) It could also be a faulty ignition sw. so you need to see if power is going to the starter solenoid when you turn the sw. and if it is, then replace the starter.
The last time I had vapor lock was on a 1961 rambler with a one barrel holly carb on it. But you know what, I still miss that fold down front seat.


#4

It’s possible that your associating the problem with filling the gas tank may be misleading. People fill with gas a few times a week, and when something happens it sometimes seems associated but it often is not.

This sounds to me like an erratic starter solenoid as already mentioned or even perhaps a starter relay. It might even be a corroded battery cable connection.

Youo can check the connections without waiting for the symptoms to reappear. You can also have the battery and charging systems checked for free at many local parts stores. Call around. If all of this checking bears no fruit, you might want to be prepared to check for 12VDC at the starter the next time it happens. If you have voltage, it’s the starter assembly, if not, check the starter relay.


#5

You are not describing a vapor lock condition, does “being dilligente on scheduled upkeep and maintiance” include any battery service? just what does that statement include, it must mean more than regular oil changes.


#6

Yes, vapor lock is extinct. And even in the past it could never happen from a cold start.

Your problem description is ambiguous. When you say “nothing happens,” do you mean the engine won’t even crank? If so, suspect an electrical problem, not a fuel problem. There are several switches that must be open/closed in order to excite the starting circuitry. You need someone who can check out the electrical system.


#7

If the dashboard warning lights are illuminated with the key on (alternator, oil, etc.) and there is nothing but stone silence when the key is turned to START you should consider the possibility of a failing neutral safety switch if this vehicle has an automatic transmission.

Next time it acts up shift into NEUTRAL and see what happens. The gasoline filling and gas cap thing is coincidental. Poor contacts in the neutral switch can be affected by movement of the car. (movement of the steering wheel, slamming the door, sitting on the seats, etc.)
Neutral safety switch failures are not a rare thing.


#8

Vapor lock was a problem back when cars had mechanical fuel pumps on the side of the engine block that sucked fuel from the gas tank and pumped it to the carburettor. If the fuel before the fuel pump boiled from the heat under the hood, the pump was unable to pump the vapor and the carburettor would run out of gas.

Today’s cars all have the fuel pump inside the cool gas tank and they deliver the fuel to the injectors at a high pressure, around 40 psi. Under 40-50 psi of pressure, gas is not going to boil and even if it does, it won’t prevent the fuel pump from delivering fuel to the injectors.
Some of the newer designs inject gasoline directly into the cylinders instead of the intake ports, these run pressures of over 1000 psi. You could most likely fill up with liquid propane, provided it was minus 25? F or colder outside, and not have the fuel boil in the fuel line on this system.


#9

Thank you all for your replies. I kind of already knew about vapor lock, “Is Vapor Lock Extinct?” was my poor attempt at car humor :slight_smile: I am planning on taking it in but I like to already have an idea what is wrong with it so I will know what to expect. I will check battery connections in the mean time and keep the solenoid/starter issues in mind. Again thank you all for sharing your infinite wisdom!


#10

I think you may be on the right track. I got in this morning, turned the key, full power on the dash but silence on the start. I put it in Neutral and it fired right up. You may be a genius! It is going in to be looked at this Friday.


#11

Believe it we know that many posts are fishing expeditions and the OP’s already have their minds made up or are looking to turn the discussion a certain way, this is why many answers at first seem off topic.


#12

Vapor lock does occur on fuel injected engines.

The fuel injection system is a closed loop system. This means whatever fuel that isn’t used by the engine is returned to the fuel tank. As the fuel is heated from the hot fuel rails and is returned to the fuel tank, it starts heating up the fuel in the gas tank. As the fuel level drops in the fuel tank, and this cycle continues, the fuel in the tank heats up. Once the fuel in the tank reaches a certain temperature and is pumped back up to the hot fuel rails it can start to boil, causing vapor lock. This is more prone to happening if the fuel contains ethanol as it makes the fuel more volatile or it boils easier.

Vapor lock can also occur when the engine is shut off. When the engine is shut off the fuel pump stops running. The fuel sitting in the fuel rails above the hot engine starts to boil and this can cause the engine not to hot start.

I’ve seen both situations occur on fuel injected engines.

Tester


#13

It would be a diservice to place vapor lock at the same point on the trouble shooting chart that it previously occupied in the mid 70’s and earlier. I know I have not had to deal with it in several decades.