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Open Roads Forum  >  Tech Issues

 > Vapor lock 1990 E350 EFI 460 engine?

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maillemaker

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Posted: 10/06/19 10:47pm Link  |  Quote  |  Print  |  Notify Moderator

Check this out:

http://www.429-460.com/t18331-460-fi-problem

Quote:

Yes. In fact, after I replaced the tank pump (low-pressure), we had the problem again, and a shop replaced the high pressure pump on the frame rail below the driver's door because they said it was running a little low. They subsequently tested all the pressures, and they were fine.

I kept a FP gauge attached to the Schrader valve on the fuel rail during one trip after that. It ran at the correct pressure (I think it was 50 psi, but that was a couple of months ago, so that may not be exact); however, as soon as I climbed a long hill in heat over 85 degrees F, the pressure dropped to zero and stayed that way through multiple attempts to restart. When I pressed the release valve on the gauge, I got nothing more than a few spurts and drips of fuel; I was halfway expecting to get a high-pressure burst of boiled fuel, but got nothing like that.

After about 45 minutes, though, I was able to start it just fine, the pressure went immediately back up to 50, and we were on our way again. That happened three or four times in one trip, and it was always the same: a drop to zero FP in a hot climb, a 45-minute wait, and a no-problem start with FP at specs until the next big climb. It has never happened except when very hot, and then only when climbing long hills. No engine overheat, though.

I got as far as removing the fuel lines from the single-function reservoir (small canister that holds fuel between the low-pressure and high-pressure pumps, similar to the function of a carb bowl in non-EFI systems); however, by the time I got all that figured out, it was working again, so I could not isolate the point at which fuel is failing to flow. And now the weather is cold, so it will probably not happen until next summer. There seems to be no way to check for the problem except when it is failing.


Sounds like my problem exactly.


1990 Winnebago Warrior. "She may not look like much but she's got it where it counts!"



sayoung

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Posted: 10/07/19 05:50am Link  |  Quote  |  Print  |  Notify Moderator

When I was a kid in the 50's, probably half the cars on the road had clothspins clamped on the fuel line to radiate heat from the fuel easing vapor lock.

maillemaker

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Posted: 10/07/19 08:49am Link  |  Quote  |  Print  |  Notify Moderator

Quote:

When I was a kid in the 50's, probably half the cars on the road had clothspins clamped on the fuel line to radiate heat from the fuel easing vapor lock.


I have heard of this, and even seen it in a YouTube video, but I find it hard to believe this actually works by radiating heat.

First, wood is not a very good conductor of heat. And even if it was, given the high under-hood temperatures, the result would actually be to wick up heat and put it into the fuel line. This is because heat always moves from hotter-to-colder.

What I suspect is/was actually happening is that wood, being a relatively good insulator was actually insulating the fuel line from the ambient heat in the engine bay. If you clamp a dozen clothes pins onto the fuel line, then all that area is now encased in wood, effectively insulating it.

Carburetor engines often put a phenolic block of plastic between the carb and the intake manifold to try and insulate the carburetor from the heat of the engine.

Steve

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Posted: 10/07/19 09:20am Link  |  Quote  |  Print  |  Notify Moderator

Do you know for sure the pump is running? Might try changing out the relay for it. They are a known failure point at higher mileages.
Some shops always replace the relay when they replace the pump.


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ksg5000

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Posted: 10/07/19 11:56am Link  |  Quote  |  Print  |  Notify Moderator

maillemaker wrote:

Evidently the fuel filter is designed to last the life of the vehicle.

[image]


When they started to modify fuel that put lots of accumulated junk in the fuel filters. Changing fuel filters isn't expensive and something that the Ford dealer recommended on my 91. Changing fuel filters would be high on my list when it came to anything that appeared to be fuel starvation - not much downside.


Kevin

maillemaker

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Posted: 10/07/19 12:23pm Link  |  Quote  |  Print  |  Notify Moderator

Quote:

Do you know for sure the pump is running? Might try changing out the relay for it. They are a known failure point at higher mileages.
Some shops always replace the relay when they replace the pump.


When the in-tank fuel pump burned up 5 years ago, it took out the inertial switch and the relays with it. So the relays have been replaced within the last 5 years.

I don't have a way to know right now if both pumps are running or not. I will be installing a fuel pressure gauge shortly.

Quote:

When they started to modify fuel that put lots of accumulated junk in the fuel filters. Changing fuel filters isn't expensive and something that the Ford dealer recommended on my 91. Changing fuel filters would be high on my list when it came to anything that appeared to be fuel starvation - not much downside.


Agree. After I get a baseline reading with the stock setup, I'm going to replace the fuel pressure regulator, fuel filter, and high pressure pump.

Steve

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