ScottyBean

So i started my 96 4runner up this afternoon.. i hadnt driven it for a while.. maybe 4 hours.. it was a warm day, so it wasnt warm and it wasnt cold.. started shaking as if it was struggling for gas or something.. after 10seconds it was fine... any suggestions?!

DudeBud

missing. was it smoking

MTL_4runner

When was the last time you did a tune up?
I would inspect all the basics (plugs, air filter, fuel filter, clean throttle body and check the IAC).

Did it throw a CEL at all?

Unhappy99

Just mild vapor lock. The fuel in the rails had boiled, and it takes a few seconds to pump liquid in and push the vapors back to the tank. Next time, try turning on the ignition to where your dash lights all come on, then count to 3, then start it.

ScottyBean

I think unhappy got it the best there.. runs fine now..

bob200587

happens to me alot, im chanign my fuel filter, which has never been changed....im hoping that will fix it.

MTL_4runner

You might want to have someone hook up a pressure guage on the fuel rail to see if you are losing pressure....unless the truck sat there for quite while (and the return got stuck somehow), you should not be getting vapor lock. I live in AZ for 5 years with my 4runner and surely if you were going to get vapor lock, that would be the place....but nope, never happened. If it was vapor lock, there is a reason for it happening.

Although I am not entirely sure this is the case....

"Vapor lock is highly unlikely with today's fuel systems. Vapor lock occurs when the vapor pressure of the fuel is higher than the surrounding environment. In older engines with "sucking" fuel pumps at the engine the pressure in the fuel line to the tank was reduced by the sucking action of the fuel pump drawing fuel form a fuel tank nearly twenty feet away, and when heated, the gasoline actually boiled creating a vapor of gasoline which the fuel pump could not handle, thus the name "vapor lock".

Today's fuel pumps are in the fuel tank where they push the fuel under pressure to the engine systems. Excessive fuel which is not used is sent back to the fuel tank. This causes a constant flow of pressurized, cool fuel in the lines to the engine system, be it fuel injection or carburetor. As a result you would have to heat the fuel line with a propane torch to get the fuel to boil and even then it would be cooled by the flowing fuel circulating from the tank to the engine and back again to the tank. Vapor lock as we once knew it is a thing of the past."

Unhappy99

"Vapor lock as we once knew it is a thing of the past"

Its still rather common that after getting the engine hot, then shutting off, the fuel in the rails gets heat soaked and boils, creating the vapor problem. Perhaps this should be called a 'hot start' problem instead of vapor lock.

It can be difficult to start and/or run rough for the first few seconds while the pump pressurizes the lines and replaces vapor with liquid. People in hot climates (including Phoenixians) and those making a 5 minute Quickie Mart stop experience this.

Since it usually takes just a few seconds to clear the vapor, nobody really notices it. If it occurs often or if it runs rough for more than 10 seconds or so, then the fuel lines should be checked for static and dynamic pressure and flow to see if the the pump and its one way valve, fuel filter and regulator are all working properly.

MTL_4runner

I certainly agree that at rest the fuel could boil if the rail pressures dropped too quickly over time (ie leaky injector, bad return valve in regulator, etc) or if the vehicle remains heated in the engine compartment to over 200 degrees for a very long time (key is fuel pressure must drop for the gas to boil). Now most people don't experience any "hot start" problem at all because in the time it takes to turn the key and fire up the engine, all vapor that existed has either been injected into the cylinders or returned to the tank. Usually the there something amiss with the system or everyone would be experiencing it not just a few.

2ToyGuy

Then it's something other than the fuel, because I know a LOT of people here that experience that effect this time of year...

Mr.mud

Its happened to my 2000 tundra maby 2 or 3 times but not enough for me to do anything about it. I live in San Jose CA not really known for hot weather.

2ToyGuy

Lucky bugger. I'm from Woodside. Oh, how I miss the Bay Area!!!