EFI vapor lock?

[Steve83]

Vapor lock means the fuel stops moving through the line; that happens when the pump's inlet is so hot that the fuel vaporizes, and acts like a spring that doesn't allow the reciprocating pump's movement to reduce the pressure in the line enough for the liquid fuel farther back to push forward through the pump's spring-loaded valves. Hence: the fuel line is locked by vapor - vapor lock.

That doesn't happen to centrifugal or positive-displacement (EFI-type) fuel pumps because, even when there's vapor at their intakes, they still move the vapor through & then the liquid fuel. So vapor lock does not apply to EFIs.

If you modify a carb vehicle cheaply, and use an electric reciprocating pump to move fuel toward a high-pressure EFI pump, then you theoretically could get vapor lock, if the fuel lines between the tank & recip. pump are routed very badly.

The foam wrap is for NVH - not heat. And it was used on '84-89 EFI F-series & Broncos.

 

[Wyflyer]

http://classicbroncos.com/forums/showthread.php?t=229521&highlight=reid+vapor+pressure&page=2

 

[sigepkat]

Here's a shot of the fuel pump - https://goo.gl/photos/LFioq5rB1qwZqCyp9
The exhaust is about 3 inches away...

I've complied the reasons that everyone has offered w/my thoughts on them (cause my thoughts are worth a hill of beans...)

- Fuel pump overheating (jw0747, sigepkat)
- leaning this way due to proximity to exhaust and it only happening in warmer months

- Bad diode in ECU (ScanmanSteven)
- could be, I assume that heat could affect the ECU

- Wire gauge too high (Jambi)
- doesn't seem likely, since I'm running the RJM harness

- Pin hole in fuel line (Broncobowsher)
- wouldn't there be an obvious leak if that were the case?

- Non-vented gas cap/vented gas cap (Wyflyer)
- I THINK my gas cap is non-vented (as in, designed for a non-vented tank) because there's no rush of air when I open the tank

 

[ntsqd]

Has it done it again, yet? Have a test light with you when it does and check for power and ground at the pump if the pump isn't obviously running. Carefully, i.e. don't stand in front of it, crack the fuel cap then too.

 

[sigepkat]

No, I haven't driven it enough to get it to do anything, but the test light and voltmeter are both in the truck so that when I do and it does I'll be able to test it.

I did email Airtex, the maker of the E2000 pump and they said there is no thermal protection in the pump, so it wouldn't overheat and shut down, but too much heat could boil the fuel and cause cavitation which would cause these symptoms.

 

[ntsqd]

Not that we wish ill, but some of us want it to happen again so it can be solved.

... but too much heat could boil the fuel and cause cavitation which would cause these symptoms.

Which contrary to one poster's insistence otherwise is also known as vapor lock.

 

[sigepkat]

Me too, it'll just suck being stuck somewhere while things "reset", but if that's not half the fun of daily driving a 40 year old truck, I don't know what is.

 

[ransil]

check for junk blocking the feed line, either in the tank or in the line/filter.
but if your pump is 3" away from the exhaust I would do something with that first.

 

[ntsqd]

A simple sheet of thin aluminum between the exhaust and the pump will do wonders IF that is the problem.

 

[jw0747]

Exactly like mine but my exhaust was farther away. Also where it is now is where air doesn't circulate too well. Here's an easier way to test. Carry a bottle of water and when it shuts down again crawl under and douse it all over with water. Then try to start it immediately. If it fires right up it is overheating.

I really like Timmy's set up in post #14. A foam anti-vibration type wrap first then what looks like a piece of aluminum wrapped around the whole deal and held in place with clamps. If that type setup didn't correct your problem you could go a step further and wrap the exhaust and add an additional aluminum shield below the pump.

 

[sigepkat]

Here's my plan for the immediate future...I've got some scrap aluminum that I can build a box/shield out of, then I'll center the pump on the rail that it's mounted on, that'll give it a few more inches of space from the exhaust. Hopefully those two moves will do the trick. Both of those seem like good things to do either way, since it should improve the life of the pump, even if it doesn't fix the problem. I'll post up some pics and updates once I've got things built out.

CM

 

[ntsqd]

Just a deflector plate between the exhaust and the pump is enough. Boxing it in runs the risk of creating an oven. You want air movement on both sides of the plate. Theoretically ideal spacing is 50/50 in the gap, reality spacing is a little more than no contact with either the pump or the exhaust will work.

 

[jw0747]

Just a deflector plate between the exhaust and the pump is enough.

This didn't work on mine. You can box in both sides and the bottom but don't install a top on the box. I would still recommend moving the pump to a frame rail as close to the tank as possible and box it in there. Looking at the photo where it's located now is a powerful oven.

 

[ntsqd]

It is enough to shield the pump from direct exhaust heat as I've done that sort of thing many times. Other sources I hadn't considered in my response.

 

[pcf_mark]

You can get EFI vapor lock in the intake manifold when the pressure drops in the fuel rail. So if your pump gets lazy (low pressure or low voltage) causing your fuel pressure to go down you can get a vapor lock like condition - it will run rough, snort and spit like it is running out of gas.

As pointed out EFI fuel pressure alone is usually enough to avoid vapor lock in the HIGH pressure side after the pump. Plus the return line acts like a natural vent for any air or hot fuel. But the low pressure line is susceptible to vapor lock from the tank to the pump. Just make sure that stays cool to the touch.

 

[sigepkat]

Ok, finally had a chance to drive it and reproduce the problem. The fuel pump is shutting off, despite getting power. When I supplied power (from the trailer plug) and turned on the headlights ( ), it would run and the truck would run, but would eventually shut down again, despite still getting juice. So where does that leave me? Fuel pump on it's way out? The pump shouldn't overheat (BTW, it showed 120-130 degrees on my temp gun) and shut down, according to Airtex. But the boiling point of fuel is between 100-400 degrees, so maybe I'm boiling the fuel. But that doesn't explain the pump shutting off...Maybe it's an issue w/the capacitors on the ECU? I'm at a loss.

 

[pcf_mark]

I would "hot wire" it for a test. #12 wire from the battery to a switch in the cab. Just wire tie it enough for a test - run it in / out the pass side window. Power it up go for a drive and see if it dies. If it still dies the pump is over heating and may have an internal shunt to protect it from burning out. If the pump is still running and it dies you boiled the fuel somewhere.

My money is the pump is toast. My experience with Airtex block mounted pumps was very negative. Buy a Bosch for $90 use a filter and you will never kill it.

 

[sigepkat]

What Bosch pump would you recommend? The straight alternative of the E2000 isn't an option, apparently (at least no one can order it...)

CM

 

[toddz69]

What Bosch pump would you recommend? The straight alternative of the E2000 isn't an option, apparently (at least no one can order it...)

CM

The OEM Bosch pump used on Ford EFI trucks with the external pump was the 69100. Very common to find these days from a multitude of sources. That's probably the closest thing to an E2000 pump. I've been using one since 1997 and it works just fine (knocks on wood).

A very similar pump is the OEM one used on late model Super Duties - the Bosch 69136.

And a real workhorse of a Bosch pump is the infamous Bosch 044 EFI pump (beware of fakes on ebay/Amazon, etc).

Todd Z.

 

[Steve83]

But that doesn't explain the pump shutting off.

Right - this issue has never been about the fuel or its temperature, despite all the background noise arguing that moot point. It's about a bad fuel pump motor.

Maybe it's an issue w/the capacitors on the ECU?

They weren't involved when you jumped power from the trailer circuit, and the motor still shut down.