I've never heard of it happening on a setup with an in-tank fuel pump, carburetor or FI. Because the fuel is constantly circulating, it never gets that hot, and the high pressure in the system (esp. with multi-port FI) keeps the fuel from boiling.
I know vapor lock was more of a problem on the older non fuel injected cars with low pressure fuel pumps mounted on the block. With the newer cars with high pressure fuel pumps in the tank with the excess fuel return to the tank, is vapor lock possible on contemporary fuel injected vehicles? What negative effects can high heat have on the modern fuel system?
BOB
I don't know if it was vapor lock, but some cars made in the 1970s with Bosch CIS fuel injection (continuous, mechanical, about 70 PSI) had hot start problems that were solved with a larger fuel accumulator. This accumulator was a bladder that kept the fuel system pressurized even when the engine wasn't running.
One thing some of the other posters haven't recognized is that with any type of fuel pump that is mounted outside the fuel tank, there is a suction line. Inside any suction line, pressure is lower than atmospheric (that's how the fuel moves--atmospheric pressure pushes it toward the point of lower pressure). Any time a liquid's pressure is reduced, so is the temperature at which it boils. (Ever boiled water at high elevations and noticed it wasn't very hot?)
Anyhow, with any fuel pump mounted near the engine, the fuel line from the tank to the pump is at a low pressure, and can be subject to heat from the environment, or from exhaust components. This is where vapor lock problems occur. Do away with any suction lines, and the vapor lock problem goes away fairly quickly.
Gerard TS 14
It is a laws of physics at work, gasses compress. and liquids do not. If one were to try pulling against atmosphere one can only draw a vacuum of 30 inches of mercury ASL, no mater how big the pump. When the pump is above the liquid, as in older cars trying to 'pull' gasoline to the pump, and there is vapor present in the line, it is not possible to extract the fluid. In the case of the pump being below the liquid, as are today's pumps there in no 'lift' on the intake side at all. The discharge side of the pump will push liquid up to the 'head' pressure of the pump. In other words, vapors are pushed on the discharge side of the pump, but can stop it from pumping on the intake side of the pump.
mike hunt
Robert Hancock wrote:
Very few vehicles built in the past 15 years or so only use a single external fuel pump. Of those that do, the 'suction' line is intentionally as short a possible. I don't know of any that have the fuel pump any where near the engine.
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