I have a 1992 RV based on a ford E350 chassis with an EFI 460. Whenever I have a long upgrade(which is pretty darn unavoidable here in Colorado :^) the RV appears to vapor lock. It progressively looses power and sputters until it dies completely. This often happens immediately after the uphill when coasting down the other side. If I let it cool off completely it then starts up and runs like nothing has happened! The temp gauge never goes near the "red" on the uphill. This problem seems to be getting progressively more frequent although that might be just the summer temps.

The RV's engine and chassis is bone stock and only has about 45K mi. on it.

My best guess is the in-tank fuel pump but I'd just as soon not try shotgunning the problem. I know I have heard of others with similar problems but I've never heard the solution! Any experience or suggestions would be GREATLY appreciated.

 

I had a VERY similar situation with a 1989 Full size Bronco. Mine was totally temperature related. Let it cool w/ the hood open and it'd start right up. It was under warrantee, and was towed to the dealer. They replaced the fuel filter (!) and that fixed it!!! (I felt a little bit stupid as I could have taken care of it). Try that.. it's an easy job.

Another thing you may want to do is get a fuel pressure test gauge that connects to the EFI rail's Schrader valve. Soon as it dies, hook it up and turn the key on... see if you've got the correct fuel pressure. Your fuel pres. regulator or pump relay may be trying to die. Also, I wonder if the 'in tank' pump's pick up screen could be getting fouled with some junk in the tank, or possibly the pump's pick-up is loose.

One other thing... check the NHTSB's Technical Service Bulletin list... there may be a TSB out on your chassis. (www.nhtsa.dot.gov)

 

Go to rvamerica.com. This problem has been discussed many time. The fuel pump may very well be the problem but the current thought on the mentioned bb is that heat build up is the problem. One of the long time members of that bb has insulated his tank, lines, and installed a cooler in the return line. Has not had a real test of his modifications yet. As someone mentioned, change the filter first. Good luck,
ray

 

I am having the same issue in my 1990 EFI 460 in my RV.

I have already replaced the ICM and PIP (with the Distributor), spark plugs, plug wires, radiator, and catalytic converter.

In-tank pump was replaced about 5 years ago. But I have not replaced the high-pressure pump.

I'm going to install a fuel pressure gauge and get a baseline reading, but then I'm going to replace the Fuel Pressure Regulator, Fuel Filter, and the High Pressure Pump.

I'm also considering an inline cooler on the return line.

Steve

 

An EFI engine cannot vapor lock as long as the fuel pump(s) are operating properly. You could be pulling a vacuum on the system, tho, if your tank vent(s) are not open.

 

I used to believe this until very recently, but now I do not think it is impossible.

This guy caught his in the act with a pressure gauge:

460 FI problem

I believe that the problem is with today's ethanol fuel blends they have vapor temperatures lower than the pure gasoline they were designed for.

When ambient temperatures reach a certain point (90F+), combined with the AC running, under-hood temperatures get high enough to boil the fuel in the fuel rail.

Evidently when this happens the fuel pressure regulator thinks there is low pressure in the rail, and so shuts off fuel flow back to the tank, in an attempt to bring the rail pressure back up again.

I'm guessing this further stagnates the flow of fuel in the rail, allowing it to heat up even more, until you have a fuel rail full of vapor rather than liquid fuel. Then the engine dies until it cools down enough for the fuel to condense back to liquid.

This fellow claimed similar symptoms and claims his problem was fixed by replacing the fuel pressure regulator:


I will shortly be installing a GlowShift fuel pressure gauge in the cab so I can monitor the pressure while driving.

I want to get a baseline reading, and then I will replace the fuel pressure regulator, the fuel filter, and the high pressure pump, and get a new baseline.

Unfortunately it looks like we have turned the corner into fall temperatures this weekend so I may not be able to reproduce the problem until next spring.

Steve

 

So it happened again today. Temps in the 90's, as usual, when summer hits, I get hit with this problem.

Had been running down the interstate for an hour. Got onto surface streets, it died literally in the same neighborhood it did this before.

This time, though, I had digital fuel pressure gauge installed. Engine temp was 194F, went to 204F after it stalled and died. Fuel pressure is normally ~40 PSI, was only reading 9-12PSI. Waited 20 minutes, engine temp dropped to 183F, and bam! Fuel pressure went right back to 40 PSI and engine fired right up and I drove home another 10 minutes.

The high pressure pump is brand new - replaced it about a month ago. In-tank pump is about 5 years old.

When I got home, I used an infrared thermometer to measure the gas tank - it was about 109F.

I think I'm going to try fuel line insulation to start with.

 

they make fuel line insulation, in sticky back now, with stands 1000* so you dont have to remove fuel line to get it on, it wraps like the header wrap, brother-inlaws 67 390 in it would vapor lock, put the fuel wrap on, it stopped.

 

Did it work?

 

yeap, stop vapor locking, looks better than the old wooden clothes pins use to put on fuel lines.

 

I thought I had gone and found all my threads and posted the solution, but I guess I missed this one.

The problem is that on these early 1990s era Fords when they switched from carburetors to fuel injection rather than redesign the entire fuel system they kept the low-pressure in-tank fuel pump and just added a high-pressure boost pump on the frame rail under the driver's seat. This boosts your pressure up to about 40 PSI for the fuel rail. Excess fuel is routed back to the tank (whatever the engine does not drink).

I installed a thermocouple on the return fuel rail leaving the engine compartment and discovered the fuel temp was about 125F going back to the tank. An infrared thermometer on the tank hull read about 110F or so after a long time of running.

The problem was the Airtex in-tank replacement pump had died. When it was pulled out to replace it, the brushes were complete gone. One was missing, the other just a nub. This pump was probably less than 5 years old and probably only had 20K miles on it or so.

The problem is this: When the in-pump tank fails, the high pressure pump on the fuel rail is strong enough that it can suck fuel all the way up from the tank, even through the dead in-tank pump. But, because it is pushing 40 PSI upstream, it is sucking about negative 40 PSI downstream. As you may know, the boiling temperature of liquids lowers when pressure drops. This is why it is harder to cook with boiling water on top of Mt. Everest as it boils at only 154F instead of the usual 212F - a delta of 58 degrees!

What I am pretty sure was happening is after a hard run and the engine and gasoline gets heated, especially during summer, the temp of the fuel is probably approaching 125F. The boiling temperature of ethanol gasoline starts to boil around 175 - a delta of 50 degrees. With the high-pressure pump pulling a vaccum in the line going back to the tank, this causes the hot fuel to flash into vapor (boil). The high pressure pump cannot pump vapor, and so you read very low pressure on the fuel rail and the engine will not run.

If you wait 20 minutes or so, the fuel will condense back to liquid and the engine will fire right up and run just fine until it heats up again and dies again.

I purchased but never installed insulation on the fuel rails. For one thing, it's hard to get at the entire run around the intake. But anyway, eventually you reach a stead-state temperature under the hood and while insulation would slow down the rate at which the fuel heats up it would not stop it. When you are going down the interstate for an hour everything is going to get hot with that 460 engine crammed in that tiny engine compartment.

The problem is that because there are 2 pumps, if the in-tank pump fails the high pressure pump will mask the failure. The engine will run just fine most of the time (though I was getting some intermittent stumbling at low speed and lugging the engine (going up a hill about 45 MPH)). It's not until the gasoline gets hot after extended running that this problem rears its head. This is why it is so hard to diagnose - it is intermittent and if you took it to any repair shop by the time they looked at it it would be dead cold and nothing would appear wrong. They would have to run it hard for an hour to see the problem.

I suspect fewer and fewer people will be owning these ancient vehicles with the 2-pump setup, so this problem is probably going to affect few people anymore.

But the short of it is, you absolutely can get vapor lock in a fuel injected fuel line.

 

But only if your fuel pump(s) are not operating properly, as I originally stated. I am NOT saying that fuel will not vaporize in the line, of course it will, but the fuel pump is strong enough to push the vapor thru the line and get liquid to where it needs to go. Fuel vaporizing in the line is not the same as vapor lock.

The HP pump can pull liquid, but it cannot pull vapor. That's why the LP pump in the tank is needed in this scenario - it can push both vapor and liquid.