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Old 09-09-2020, 04:03 AM   #1
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F53 fuel tank vented or under pressure?

On the F53 V10 should the fuel tank be pressurized when the engine is running?
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Old 09-09-2020, 05:36 AM   #2
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Quote:
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On the F53 V10 should the fuel tank be pressurized when the engine is running?
Itís not pressurized or vented - itís a closed system. But because itís not vented, a certain amount of vapor pressure will accumulate in the tank due to the physical properties of gasoline. So you will likely get a little vapor release when you open the cap, especially on hot days, but that is normal.
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Old 09-09-2020, 07:14 AM   #3
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R. Wold,

Excellent short, concise and correct response. Every vehicle made since 1980 has had a fuel EVAP sealed system. The PCV (Positive Crankcase Ventilation) system came in the mid 70's so maybe they were somewhat sealed before 1980.
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Old 09-09-2020, 03:00 PM   #4
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Thanks for the explanation gents.


If the system is closed, what replaces the vacuum created by burning (removing) 70 gallons of fuel from the 80 gallon tank? Does the PCV control this or the vaporization of the fuel in the tank? Maybe the the PCV is like a check valve that allows air in but not out?





In addition when the engine is running at high throttle, like 80-90% on a grade, the pressure in the tank should be near zero?



Not being argumentative, just ignorant and trying get educated.



I am trying to understand why I see a lot of posts that the engine fuel pump can "starve" the aux generator of fuel.



Thanks again for the help.
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Old 09-09-2020, 03:29 PM   #5
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Have been looking on the web for info and found this dated 2015 for cars, not the f53. Maybe this is what compensates for pressure changes, keeping it pressure neutral?





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Old 09-09-2020, 04:38 PM   #6
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Thanks for the explanation gents.


If the system is closed, what replaces the vacuum created by burning (removing) 70 gallons of fuel from the 80 gallon tank? Does the PCV control this or the vaporization of the fuel in the tank? Maybe the the PCV is like a check valve that allows air in but not out?

In addition when the engine is running at high throttle, like 80-90% on a grade, the pressure in the tank should be near zero?

Not being argumentative, just ignorant and trying get educated.

I am trying to understand why I see a lot of posts that the engine fuel pump can "starve" the aux generator of fuel.

Thanks again for the help.
Well you have at least three separate issues here.

The PCV vents the crankcase gases (positive crankcase ventilation) and sends them along to the intake to be burned by the engine. This both prevents pressure build-in the engine and sends said gasses through the emissions system. But it’s not part of the fuel system.

The fuel system is closed in that it doesn’t vent to the outside, but it does constantly equalize or your tank would collapse. It has an evaporation control system (EVAP) which allows filtered air in and purges excess pressure to the intake as necessary. So your fuel cap is sealed against both pressure and vacuum. A quick look at the lines running to and from the tank will explain this - there’s not just one line out.

I’ve never heard of the engine fuel pump starving the generator and it doesn’t make sense unless it’s installed wrong. The genny has its own fuel pump. But it draws fuel from about the 1/4 tank level so at that point the generator is out of gas but the rig isn’t and that might be what people are experiencing.

And I don’t see anything argumentative here - just an interest in how things work. Interesting conversation but I have to go. More later I’m sure.....
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Old 09-09-2020, 05:12 PM   #7
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Yep, you are correct, the evap system does the equalization work for the tank pressure. If the evap was not working I would guess the tank would eventually have negative pressure and the engine would stop due to fuel starvation.


Found this link to the Ford F53 in particular:


https://www.motor.com/magazine-summa...ation-testing/


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Old 09-09-2020, 10:13 PM   #8
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As fuel is used from the tank air enters through a vacuum valve in the gas cap. That keeps the pressure equal and no fumes escape from the tank.

If the vehicle is setting and the fuel heats up and expands those fumes are collected in the charcoal canister and purged by drawing fresh air in and through the canister and run into the intake mixed with the incoming fuel charge and burned. That charcoal purging is controlled by the PC.

The RV generator draws fuel from the tank but the opening is at 1/4 tank level so the genny won't burn all your fuel. Again as the genny burns fuel air is allowed to enter through the gas cap vacuum valve.

Remember back in the mid 80's when a CEL came on because folks didn't tighten the gas cap correctly??? That loose cap defeats the EVAP system.

The PCV system is only designed to positively remove crankcase gases which are fuel fumes, combustion gases, moisture etc, etc. There's always some compression gases that get into the crankcase past the rings and is called blowby. The PCV system is separate from the EVAP system. They both accomplish similar results but do it within each system.

Those crankcase gases are pollutants and if not purged are responsible for a nasty oil sludge build up. That was one very, very good benefit when the PCV system was first implemented in CA. The old draft tube just didn't do the job.
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Old 09-10-2020, 01:50 AM   #9
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So a closed system is vented through the Evap (via charcoal canister) on positive pressure and vented through the gas cap on negative pressure?



Sure sounds like the generator should not be affected by the engine running under load.


Thanks for explaining, I now know enough to be dangerous.
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Old 09-10-2020, 10:05 AM   #10
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"So a closed system is vented through the Evap (via charcoal canister) on positive pressure and vented through the gas cap on negative pressure?"

Consider this. The EVAP system is seldom ever worked on. It is controlled by solenoids, vacuum vents etc. When the charcoal canister needs to be purged a solenoid is opened allowing gas fumed air to vent or released into an air flow that goes into the intake manifold to be burned with a charge of 14.7:1 AFR.

What determines when the CC is purged is anybodies guess.

I started my teaching career in 1971. In 1979 and 1980 the world changed. I never stopped going to summer classes and seminars. In all that time very little was ever discussed concerning the EVAP system. Seldom if ever did we work on it either.

The gas cap has a vacuum valve so if air is needed to equalize pressure in the fuel tank air enters. Nothing escapes unless there's pressure in the tank when the gas cap is removed. Remember the gas fill up handles that had a rubber hose that went in and around the gas tank fill up pipe. They were supposed to take in the gas fumes exiting as the tank is filled. Can't say I've seen to many of those in recent years.

It was kind of like the very expensive and worthless machines we had to use when working on a brake job. A sealed container to surround the brake rotor or drum so we could could contain the work area and vacuum the asbestos dust into a container to be properly disposed into the trash container.

I saw them demonstrated but doubt you'll find one in use today. We simply used water to rinse the dust off and flush it down the drain. I think the asbestos was removed back in the mid 80's or 90's.
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Old 09-10-2020, 11:15 AM   #11
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Thank you R.Wold and TeJay.



This explains issues I have had on vehicles in the past.
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Old 09-10-2020, 11:50 AM   #12
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A genny uses a separate line from the fuel tank. It won't draw below 1/4 tank leaving you that amount to find fuel. Genny operation will not affect engine operation beyond the use of fuel.

I guess for those using standard fridges they might need to run a genny while driving. Unless they can run an inverter for the fridge while driving. We have the propane/electric so that's another thread.
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Old 09-11-2020, 03:49 AM   #13
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Quote:
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A genny uses a separate line from the fuel tank. It won't draw below 1/4 tank leaving you that amount to find fuel. Genny operation will not affect engine operation beyond the use of fuel.

I guess for those using standard fridges they might need to run a genny while driving. Unless they can run an inverter for the fridge while driving. We have the propane/electric so that's another thread.

I think the OP wants to run roof top AC's while driving in the thread I am following.


https://www.irv2.com/forums/f258/gen...ng-502662.html
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Old 09-20-2020, 10:32 PM   #14
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If it is the gas cap that vents, and it is faulty, it could easily make the generator not run, and yet have little impact on the RV engine.

The carbureted generator runs at about 6psi, the fuel injection pump runs at about 30 - 50 PSI. It can over come a vacuum that can leave the generator starved.
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