Vapor lock question

[Bootybandit]

After I replaced my holley with the Carter, I pulled the fuel sending unit to replace the float.  I noticed a second cap on the gas tank that had a small hose connected to it running to nothing I assumed it was a vent for the tank (edit) Its running to a metal line that runs to nothing.  I'm now experiencing what I think is vapor lock.  Heat index is at 105 here in louisiana.  After I get close to op temp I notice the clear fuel filter I bought has little no fuel in it and she go's kaput.  
2 questions here.

1 does this sound like vapor lock?
2 is that little hose a vent or a return for vapor system with 3 nopple fuel filter?

[Gary Lewis]

No, that doesn't sound like vapor lock.  That would usually happen after you've driven far enough to get everything really hot.  That sounds like you are pulling a vacuum on the tank.

The little hose used to go to a vapor recovery cannister below the battery.  But it sounds like it has been removed or disconnected.  So the hose may be plugged. or pinched, which causes the pressure in the tank to drop down when the pump pulls some fuel out and eventually there's a vacuum that prevents fuel from flowing.

You can check that by removing the fuel filler cap and driving the truck, although you might want to stick a rag in so no dirt gets in.

[mat in tn]

just turn the cap to the unlatched point and leave it sitting in place. the seal will be relaxed enough. the small steel line that runs from the front may even be rusted closed.

[Bootybandit]

Thanx guys I'll blow in the vent and see if its blocked.  

[Bootybandit]

Pulled the little booger and this is it.  Internet says its a vent.  After idling until it hits operating Temp I start to loose fuel in the filter it gargles until the filter is empty and off she go's.  These are my guesses??

1. Vapor lock
2. Fuel pump going out once it gets hot
3. Filter being aftermarket
4. Tank too close to empty (idk just guessing)

[mat in tn]

I think it's time to test the fuel pump.

[dirtymac]

We're from Louisiana as well.  Last Summer I thought we were experiencing vapor lock in our truck.  We had just gotten it and the heat was about like it is now.  I was certain it was vapor lock.  We ended up having a bad fuel filter  Obviously, you have a clear filter so that's not it.

I will add that any kind of opening on a vehicle is fair game to mud dauber and wasps this time of year.  I've pulled two off the truck in the last week.

[ArdWrknTrk]

I was going to say mud dauber.
It's also not uncommon to find them in the axle vent, and people think they have bad hub seals...

It could well be crap in the tank has the pickup 'sock' all jammed up.
You could try putting another 5 gallons in and blowing back through the fuel line to dislodge any rust or varnish deposits.

The rollover valve needs to equalize pressure so the tank doesn't see vacuum.
I've run a piece of tygon fuel line from the check valve up the filler tube, terminating in a Toyota/Lexus transmission vent that is up above the filler pocket of the bed.
This setup seems to work fine for me, but I live north of NYC, and certainly don't experience gulf coast heat.

ETA: Is your Bronco the 2 barrel electronic or the 351H.O. 4V?

[dirtymac]

We had the door to our washroom open yesterday for about 6 hours while we were working on the truck.  That was long enough for a dauber to build an entire nest.  I had no idea they could work that fast.  He got evicted :)

[ArdWrknTrk]

Bees and their kind are very industrious, hence "busy as a bee"

You should see wasps and hornets build paper nests!

[Bootybandit]

Ever open up a dobber nest?  Full of catatonic spiders, what a way to go.  I also noticed I dont have a pick up screen on the sending unit. Im gonna fill it up and add a screen to it.

[ArdWrknTrk]

Yes!  🕷️

[Bootybandit]

Well, Added more gas cleaned the lines put a new screen on the pick up tube cleaned the fuel filter and AS SOON as i start to hit operating temp The filter begins to be less and less full until its struggling for fuel again.  Got to be the Fuel pump?

[mat in tn]

have you tested it? you are probably correct, yet you will be more confident if you test. it's strange that it works on a cold start though. I can only guess as to why.  
this is NOT a diagnosis! just a theory. after sitting in this heat overnight, the carb may have dried out enough to lower the fuel level and lessen the resistance of the needle and seat. allowing less head pressure to the pump, allowing it to move fuel even at a lower pressure... as it gets full and shuts off the seal then the head pressure could be keeping the pump from drawing from the tank if there is a breach in the pump diaphragm.  unfortunately, the pump is awkward to get to on this vehicle. try to do it from underneath even if you have to remove the oil filter to have somewhere to swing a wrench. if not then it is easiest if the power steering pump is out of the way first. this can include removal of ac, power steering pump assembly including brackets. they do not need to move far, just a few inches forward. and there is the power steering support bracket that arches over the fuel pump and shares the mounting bolts. I'm sure all of these are spotless clean, and color coded for easy access like mine. haha

[ArdWrknTrk]

I can't find the 351 in the 85 or 86 EVTM's Gary has posted.
If it were a 460 I'd say it is getting full voltage in prime (while cranking) and the pump is too sluggish to provide fuel in run (with the resistor)
But I only know HFH, and not whatever a 351 Bronco is wired like.
I still don't know if it is EEC IV (2V) or H.O. (4V)

[mat in tn]

well, I was assuming 4v as that's all I have dealt with in f series. I hadn't considered the early tbi like some cars got.

[ArdWrknTrk]

Not injection.
150 trucks (and Bronco's) got the feedback carb, or could be optioned with the H.O.

I'm trying to make sense of this, but I don't know what we're dealing with.

[Bootybandit]

Its a mechanical pump, and I cant literally watch the fuel drop out of the filter at exactly the same point in time.  How would I test the pump?  I do notice that when it starts to drop its almost like air is in the line, as it bubbles up into the clear filter with each stroke of the motor.  Im going to check the tightness of the pump.

[ArdWrknTrk]

Ok, so it's definitely an HO that came with the 4180.

How is your oil level?
Does it smell like fuel?

[Bootybandit]

Oil level is a low and I FEEL like it smell like gas, but now that I've smelled it about 10 times idk, I may be high now.