High Pressure Vapor Lock

In an earlier column you answered a question about vapor lock with the suggestion of adding a second electronic fuel pump among other remedies. Last year I bought an older (1993) Ford 350 Frontier Flyer. The main difference is that it is fuel-injected but I believe it, too, is vapor locking. Some people I have spoken to were surprised it is fuel-injected and said that they had never heard of a fuel-injected motorhome vapor locking. Can vapor lock occur in a fuel-injected engine and if so, do the remedies you suggested in the earlier article apply? If not any ideas on what it may be? It is definitely a temperature related issue because after it cools down it will run fine.

Dallas, (Salt Lake City, UT)

Yes Dallas, vapor lock can occur when using an in-tank high pressure pump to deliver fuel to the engine. It is my belief there are at least three possibilities that may cause the problem you are experiencing.

First, Ford had a recall on in-tank fuel pumps and pressure regulators for 1990-93 model year vehicles. It is possible that your in-tank fuel pump or pressure regulator may be a faulty component. Others agree with me that you should focus on the pressure regulator first, because if it fails it would not allow fuel to return properly to the fuel tank. This could cause the vapor lock problem because it would literally boil any stagnate or stationary fuel before it gets to the injector. Have an engine mechanic confirm that the pressure regulator is within factory specifications.

Second, as mentioned above, the in-tank fuel pump itself may be the problem. That in-tank pump is of a type that is highly susceptible to damage from contamination. As the pump begins to wear, its output becomes weaker. If the pump is weak, the vehicle will lose power after the pump has warmed up. Again, have a technician confirm that the output pressure of the pump is within factory specs, especially after the engine has warmed up.

And thirdly, the final possibility is that the fuel lines may be heated beyond design parameters. This typically happens when the fuel lines and exhaust manifold follow each other too closely along the frame rail. This could be the result of a faulty catalytic converter or it could be the result of ill-placed or missing heat shields in that area. For more specific information regarding the specs for your chassis, I recommend you contact Transfer Flow Inc., in my opinion the premier authority on all things relating to RV fuel containers. Feel free to contact Bill Gaines at: bgaines@transferflow.com or give them a call at 800-442-0056.