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Topic: Fuel line Question- Relating to Earlier Prime Problem (Read 443 times) previous topic - next topic

Fuel line Question- Relating to Earlier Prime Problem

Hello again everyone.

In an effort to get fuel into the line after changing my primary fuel filter, I did all of the recommended cycling of the transfer pump etc. without success. 

I was given advice to put some compressed air into the fuel tank with the filter loose.  When the fuel begins to spill out at the filter screw it on and then back to cycling transfer pump. All should be good.

I could not get it to start and decided to check the filter and no fuel was present.

I tried to use the air into the tank method again and now I cannot get fuel to reach the filter.  Tried a number of times.

I decided to remove the filter, take off the fuel cap and blow back to the tank to see what would happen.  I got a piece of 3/8 tubing, sleeved my air nozzle and put it into the inlet of the filter housing.  I wrapped the tubing with a rag to get a seal.  We were able to hear bubbles being made in the tank.

We then went back to putting air into the tank to prove the line is good.  No fuel reaches the filter housing.  When I remove the hose from the tank air pushes out which makes me feel there should be no leak in the fuel line.  No sign of a leak anywhere and no diesel smell.

I thought we had pushed an obstruction back into the tank but without getting the fuel to make it to the filter, I feel as though there must be something I do not understand about the unavailable "flow diagram".

I am under the assumption that it should not take much air pressure to move the fuel from the tank to the filter.  I am apprehensive about over pressurizing the tank as the aqua hot and generator lines would also be subjected to pressure.  Our first and only time getting fuel to move into the filter was when I was really using as little pressure as possible.

Any thoughts?  As of now, we can't start the coach.

-FT
2001 U270- 34'
with Aqua-hot
Travel Safely
Have Fun!!

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #1 –
Your tank has a vent tube that you will find near the center of the front bulkhead.  They are noted for getting stopped up with dirt daubers if not stopped up that is where your air pressure is going.  Your vent tube boss on the top of the tank has a check valve in it to keep the vent from leaking fuel out the vent line in case the coach ends up on it's lid. It will let air pass but stop fuel. One other thought is if you have just a minimum amount of fuel you will need more pressure to get the fuel over the hill.  You may have to plug the vent tube to get enough air pressure just remember LITTLE PRESSURE as there is a lot of square inches in that tank.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #2 –
Thank you Mike.

For clarification, do you think more air pressure is needed to push the fuel to the filter?
2001 U270- 34'
with Aqua-hot
Travel Safely
Have Fun!!

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #3 –
Personally I wouldn't pressurize the tank, rather than that I pull a vacuum on the fuel line. I have a vacuum tank that the vacuum pump is tied to. A hose goes from this tank to the fuel line. When fuel come to this tank then lines should be full. To make this work you need to install a valve to be able to shut off till you get all the lines hooked up or the fuel will leak back.  If this happens then you are back to square one.

Mike

If you are going to use pressure then according to what you describe then you most likely need more pressure to get the fuel to get up to the hose level.

Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #4 –
And, of course, raising the front end will make the whole process easier-- it is level of fuel in the tank VS filter housing that determines whether fuel will flow toward the filter or tank. And, in the future, more fuel in the tank will also help with direction of flow.

Gravity WORKS.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #5 –
FT to take mike's comment a little further down the road-- these tanks are not pressure tanks --you can cause one to split at the seams(welds) if it is over pressures-- I have pressured a tank before and at less than 10psi it started making noise so be super careful with the pressure
Just my thought
Chris
1999 U 320 DGFE
Build Number 5523
Chris & Elka Lang
In the field, Lonoke AR

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #6 –
UPDATE:  First of all thanks for everyone's support.

The newbie RVer finally had enough.  I gave the tank more pressure and finally had a solid stream coming out.  Enough to fill my catch container before turning the filter a couple of turns to seal it.

I am going through the cycling of the transfer pump now.

Chris, I did not discount your feelings on the pressure.  This was a risk I decided to take based on all circumstances here.  I am going to look into your solution down the road.

I will let you guys know if I get a start.

-FT
2001 U270- 34'
with Aqua-hot
Travel Safely
Have Fun!!

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #7 –
Quote from: Chris m lang –
FT to take mike's comment a little further down the road-- these tanks are not pressure tanks --you can cause one to split at the seams(welds) if it is over pressures-- I have pressured a tank before and at less than 10psi it started making noise so be super careful with the pressure
Just my thought
Chris

Good caution, but if you are using your hand as a "seal" and the air nozzle, there is NO WAY you can over-pressurize the tank.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #8 –
Ft,

It may stumble for a little bit but I bet it will fire right up and clear up after a short time.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #9 –
UPDATE #2-

No start yet.  Maybe secondary filter? 

Transfer pump sounds like it is doing its thing,  Tried for 30-45 minutes and decided to regroup in the morning.

No panic yet.  I don't have to move out for a couple of days.

-FT
2001 U270- 34'
with Aqua-hot
Travel Safely
Have Fun!!

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #10 –
Quote from: Chris m lang –
FT to take mike's comment a little further down the road-- these tanks are not pressure tanks --you can cause one to split at the seams(welds) if it is over pressures-- I have pressured a tank before and at less than 10psi it started making noise so be super careful with the pressure
Just my thought
Chris
10 psi is a lot. 24 inches tall by 96 inches wide equals, 23040 pounds of pressure. Yikes. Just on the one  side. Seems like I recall the coast guard requiring much less to certify boat tanks. 3 1/2? Don't quote me on that.
Scott

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #11 –
Based on the size of the fuel tank......... I wouldn't advise putting 10 psi on the tank. No way. Hopefully your fuel cap or vent will protect it from over pressurization.
Justin & Cathy Byrd
1995 U280 "Old Faithful"
36' Build #4673
C8.3 Cummins
Allison MD3060R 6 speed - retarder
Powertech 10KW  4cyl Kubota

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #12 –
FT,

 With you running the system dry you still have quite a bit of air between that primary filter and the lift pump on your engine. If you just got the fuel to the primary filter. That lift pump don't like to pump air so you may have to get fuel primed through the secondary filter and up to the pump by breaking the fuel hose fitting right where it goes into the pump.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #13 –
Thanks Mike.  So a little more compressed air into the tank, with the line into the CAPS pump cracked open until fuel is present.  Correct?
2001 U270- 34'
with Aqua-hot
Travel Safely
Have Fun!!
 

Re: Fuel line Question- Relating to Earlier Prime Problem

Reply #14 –
UPDATE #3-

FT RoadTrip is back in business baby!!!

All advice was awesome.  Thank you.

I changed out the secondary filter and repeated pushing fuel up from the tank until it streamed down the side of the filter.  Tightened it.  Pumped the rubber prime pump on the top of the housing until firm.

The Cummins manual for my engine showed a method to bleed the line at the CAPS.  I verified this with the authorities and followed the book.  ( The authorities were not admitting to being aware of the air in the tank method)

Cycled the transfer pump probably 10 times.  Gave it a go and it started on the 2nd attempt.  I was watching in the side view mirror and did not really see any dark cloud of soot or anything.  It was not even a rough start.

I let it run to get air into the suspension again. 

I am not sure why this situation occurred, but all is well that ends well. 

I thought that when I replaced the transfer pump a year or so ago that I would run into problems.  That went really smoothly.  I guess you never know.

Thanks again.

-FT
2001 U270- 34'
with Aqua-hot
Travel Safely
Have Fun!!