When the engine is warm, its hot outside, and I stop at a light, the RV will frequenly suffer from vapor lock. It keeps idleing fine but will stutter and nearly die when I give it gas.
Turns out the intake manifold has an exhaust passage through it. This allows the exhaust to warm up the carb and keep it from freezing. That was the idea anyways. When its summer though, that exhaust passage simply serves to boil your gas and create vapor. The engineers surely had a good reason to add that exhaust passage on the intake manifold, but from my vantage point it was a dumb move that causes me nothing but trouble.
The right fix would be to block off that exhaust passsage, or just get a new intake manifold without the passage. Or just install fuel injection to increase the fuel pressure to prevent vaporization. Both of those are out of my cost and schedule for the moment.
I opted instead to install a low pressure electric fuel pump in the hopes that it kept the pressure ever so slightly higher to prevent vapor lock.
Good news, the fuel pump did indeed solve my vapor lock issue.
Now for the bad news. This install was annoying. Besides getting covered in gas, I had to keep coming back to fix things. Oh let me list my annoyances so that future generations know what they will run into.
1. No one makes low pressure in-line electric fuel pumps any more. I didn't realize just how rare these are these days. The RV calls for 5.5 to 6.5 PSI. The only inline pump in the right ball park is the Edelbrock 17301 at 4-7 PSI. I am glad it works, and I trust the brand, so I don't necessarily need more options. But this is it.
2. The RV uses 3/8" fuel hose. Said Edelbrock pump uses screw-in 5/16" barbs. No problem, just buy some screw-in 3/8" bars. NO. Idiot. Only one of the barbs on the Edelbrock is screw in and can thus be replaced. The other is permenantly fixed to the pump. So you will have one side with the correct 3/8" hose barb while the other side is the wrong size at 5/16". Get your adapters or hoe clamps ready.
3. When I first hooked up the pump, I had it pull from one tank and push into the fuel selector valve. That was the most sensible solution so the pump only ran when I had that tank selected. NO. Idiot. The fuel selector solenoid was shot and wasn't actually blocking off any tanks. The engine was seeing 2 PSI of fuel. The other 5 PSI was being used to fill the other fuel tank. The electric pump was effectively just a quick way to transfer gas from one tank to the other. That ain't gonna work.
4. So I replaced the fuel selector solenoid valve thingy. The new solenoid says very clearly not the pressurize either of the inputs. This means I need to put the fuel pump on the output of the solenoid. That isn't a problem per-se, but that means I need to run the electric fuel pump all the time. No matter what tank I am pulling from, the electric pump is in-line.
5. And the final insult, you can't pull fuel through the electric pump when it is off. Despite what I said during the video below, I later completed my test and confirmed, if you turn off the electric fuel pump, the mechanical fuel pump won't pull gas through it. The carb will eventually run dry and the engine will die.
6. Because I powered the Edelbrock pump off the same circuit as the fuel selector switch, it only pumps when on the aux tank. So now the switch on my dash allows me to select the aux tank and get fueld through the electric pump. Or select the main tank, and get no fuel from any tank thus ensuring my engine dies minutes later. Not much of a choice. I could rewire it, but I think I will just go to fuel injection instead.
So ultimately the Edelbrock pump does work great. But when combined with the fuel selector solenoid and using the same wiring, it doesn't provide any reliable fail over. If the electric pump fails, the RV won't run on the existing mechanical fuel pump.
That said, I successfully did my 3700 mile road trip without a single fuel hiccup.
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