Vapor Lock

I have a 2015 Expedition that has suffered vapor lock a couple of times over the past year. Once was after sitting at a road construction stop for 20 minutes on a 100°+ day. Another time was on a day that was 85° and we had stopped for lunch while on a road trip.

The first time, I had the truck towed thinking the problem was either a throttle housing problem or fuel pump. The tow truck driver, after much quiet thought, suggested it was vapor lock. And, that after allowing the truck to cool down, filling up with gas, and adding a couple of ounces of engine oil to the gas tank might fix the problem. It did.

The second time we let the engine cool, filled with gas and then were able to drive on without problems.

Now, I've been lectured by several mechanics at Ford and independents that it is impossible to have vapor lock on this truck since it has fuel injection.

So, my question is whether anyone else has had vapor lock problems with fuel injected engines?

bmtndog said:

I have a 2015 Expedition that has suffered vapor lock a couple of times over the past year. Once was after sitting at a road construction stop for 20 minutes on a 100°+ day. Another time was on a day that was 85° and we had stopped for lunch while on a road trip.

The first time, I had the truck towed thinking the problem was either a throttle housing problem or fuel pump. The tow truck driver, after much quiet thought, suggested it was vapor lock. And, that after allowing the truck to cool down, filling up with gas, and adding a couple of ounces of engine oil to the gas tank might fix the problem. It did.

The second time we let the engine cool, filled with gas and then were able to drive on without problems.

Now, I've been lectured by several mechanics at Ford and independents that it is impossible to have vapor lock on this truck since it has fuel injection.

So, my question is whether anyone else has had vapor lock problems with fuel injected engines?

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Vapor lock went out with the hula hoops. Give it a fuel pressure check, many parts stores will loan that tool.

Well, we did fuel pressure tests both times, and it was normal. Could be intermittent, I guess. One of the codes thrown was low pressure, but this could not be duplicated in the shop.

bmtndog said:

Well, we did fuel pressure tests both times, and it was normal. Could be intermittent, I guess. One of the codes thrown was low pressure, but this could not be duplicated in the shop.

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I would put a new fuel pump and filter in it for starters.

Your multiple mechanics are completely wrong that modern fuel injection eliminated vapor lock. Greatly reduce, sure. But to declare it impossible is rather ignorant.

It is nowhere near as common but still completely possible under certain circumstances.

for starters, a ton of the Jeep 4.0 engines suffer from vapor lock when they are subject to extreme temperatures. The intake and exhaust manifold are basically interwoven and the rear most injectors generally get vapor locked in the right conditions. I have owned 3 and I'm very familiar with it. My Turbo Camaro also suffers from it on hot days because of the single turbo system I fabricated. I have since added heatshields to the exhaust pipe and fuel lines that fixed the issue.

Vapor lock happens when the fuel is super heated and starts to boil in the fuel rail/line. It generally only shows after you heat soak the system while sitting in traffic or idling then shut the vehicle off. because the fuel is no longer flowing and cooling the system, it can start to boil. Return-less fuel systems like the one on my 09 5.4 Exyp are extra susceptible to this because the fuel does not constantly recirculate and cool the entire system like the return systems. They generally rely on keeping the fuel under higher pressure with a check valve to raise the boiling point, on top of adding heat shielding in key areas.

On modern engines that is going to be generally caused by missing heatshields allowing an exhaust pipe, or maybe cat to super heat the fuel. Or a bad check valve allowing the system to depressurize lowering the boiling point allowing the fuel to transition to a gas. . .

With all of that I have no idea what engine or fuel system you have, I would look for missing heatshields, and as 07navi said, its probably the fuel pump. Everything is incorporated inside the fuel pump assembly on these newer vehicles, Pump, check valve, regulator, that jammed it all in the pump assembly.

I would rent a pressure gauge and make sure your system is making good pressure and holding pressure. If your system looses fuel pressure in less than X minutes you might have a bad check valve. X because I don't know what engine you have.

For added information, My 09 Expy 5.4 has seen a lot of 110+ degree days (a few 120 degree days) while idling, stops and restarts and never had a single issue restarting it. It gets really hot here and we have not had a single issue with any hard starting or vapor lock.

GOOGLE SEARCH:
https://axleaddict.com/auto-repair/What-is-Vapor-Lock-and-How-to-Fix-It

Thanks for all the inputs. The truck is a 20015 Limited 4x4 with the 3.5L Ecoboost V6 engine, 6 speed auto transmission. I am testing fuel pressure on Wednesday.

I've been able to "solve" this issue (meaning I could drive without any issues subsequently) by filling the gas tank and pouring about 2 ounces of 5W30 engine oil into the fuel tank. In both cases the truck had also cooled down quite a bit, allowing it to sit without running and in shade for about an hour.

Maybe filling the tank affects the pump performance...

May have a bad gas cap but that should throw a code.

No gas cap on this model

bmtndog said:

No gas cap on this model

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Still have gas cap, just built-in. But wait ... the "old style" gas cap did more than just close it off. The new one is just closes it off. Did they add the "old style" function somewhere else in the system? I'm confused. I'm not even sure the new one closes it off from a pressure standpoint, that might be done by the new filler tube thingy that makes you require a device to get it open to put fuel in. Now you need a college degree to understand how the gas cap works!

https://patents.google.com/patent/US6994130?oq=ford+gas+cap