Fuel return line

[JAG1]

Some kind of Check ball valve...... I don't know.... has to have something when you think how much pressure being generated by the VP.... enough to blow your finger and hands apart and have to be amputated.

 

Dripley is the chicken good enough to go there often for lunch? They got one here in town of Clackamas, Oregon. Have to give it a try.

Edited December 9, 2016 by JAG1

[dripley]

I kept trying to find a diagram of the head to see how the excess fuel from the injection event gets to the return but never could. But if the fuel could leak out of the return in the tank all it would have to do is drain all the way to the tee and bye bye prime. Cant imagine how long it would take though.

 

The food and the service is top notch. But dont get me wrong there are very few places I will go out of my way or wait in a long line for a sandwich. I eat out so much it does not mean much to me for the most part. Almost a necessary evil.

[Haggar]

Guys,

There is no pressure if there is no resistance to flow....  Think on that for a second.

 

If you took all your injector lines loose and ran the vp, how would the diesel look coming out?  would it shoot across the room and cut a hole in a wall like a pressure washer?  or would it dribble out or maybe just go across the valve cover and land on the passenger fender?  (when we bleed the injector lines, they dribble and might spray a little bit, but only when you are close to tight.  They do this because there is no resistance, and resistance builds as we close the connection to the injector)  (I am attaching a picture of GM 6.5 type injectors (also on ford tractors and other things.  See the small rubber hoses?  That is the "high pressure fuel return".   The pressure drops so quickly, that hose is fine even though its POTENTIAL pressure is in the 1,000s of psi.)

 

The VP only makes pressure when it sees the resistance of the injector.  The vp puts a volume of fluid out.  When that volume of fluid is greater than the springs in the injector, the injector opens forcing fuel into the cylinder. As the VP is ending that cycle for that injector, the volume of fuel reduces so the springs in the injector close the injector.  The slight bit of high pressure fuel that is left over from the event, but not enough to make the injector open, spills into the rail in the head and goes back to the tank.

 

The reason that this fuel flow does NOT seem to have pressure is:  The return line has little to no restriction, so there is no pressure, just volume. 

 

 

This circles us back to since the return rail and fitting at the back of the head are the highest points, any air that comes in  immediately helps draining the whole system...   The check valve that is on the outlet of the VP is not perfect and it has a little bleed in it, so there is nothing to stop it from completely draining.  Air at the back of the head,will basically drain everything. 

 

You can model this at home.  Take a pail of water(diesel would be better, because viscosity matters, but is messy) and some clear tubing (cheap PVC stuff at the hardware store is perfect).  Put all of the tubing in the water and slowly maneuver it until there are no air bubbles.  Now leaving the ends of the tube under the water, lift the center of tubing as high as you want.  Do air bubbles ever develop?   Now take one end of the tubing out of the water.  Does it allow air to come in?  Do air bubbles develop?   now poke a hole in the tubing.  What happens to the water?     Now take some measurements and lay the hose like it rides in your truck,  pretend the bucket is your tank.  Hold the return end 6" above the level of water in the bucket.   have the mid part of the hose about 12"  above the pail.  (not the water level in the pail, the pail itself)  (12" is what i estimate the head collector fitting is in height relative to the top of the tank)    what happens to the water?  Where does air go to?  you can put a tee and such to model it completely.   now factor in JAG returns to the neck.... well above the tank height.  Put a droop in the line for his situation and make a leak at the same point.....   Its a great idea!   even with a small leak up high, he traps a bunch of fuel down low minimizing the trapped air!

 

My $0.02   

 

MERRY CHRISTMAS!!!!

 

Hag 

 

 

[JAG1]

Nice write up Hag. You put some time in that, Thank you and Merry Christmas. 'tis that time of year.

[dripley]

That was my thinking also. I was trying to find a diagram that showed what happens in the head. I knew the excess flows into the return just how it was interconnected.

 

When I bleed my system I open the lines very loose so as not to spray fuel everywhere and it just squirts out loosely and runs of the back of the engine. Barely cracked them open one time and they spray fuel all over. Did not like that very much.

 

Thanks for helping to explain all that.

 

Merry Christmas back at all of you. 

[notlimah]

Alright guys, I just spent way more time in paint then I'd like to admit, but I think it shows what I'm thinking COULD be the issue here.

 

 ***images not drawn to scale ***

 

 

This image shows what the fuel system would look like with the tank pretty full, on level ground. The fuel module is completely submersed and in this state I don't have any issues starting.

 

 

In this image (and this is where things get to be a bit more crude drawing wise) you can get an idea of what the fuel would look like in the tank if the tank were full, but parked uphill. Again, every hose on the fuel module is submerged in fuel even though fuel is sloshed more towards the rear of the tank. No problems with starting in this situation.

 

 

This image shows what things look like once fuel levels start getting lower. I'm saying this is 1/2 a tank and you can see that even though it's only at 1/2 tank, all of the fuel module hoses are still submerged. I don't have issues with starting in this position either. I can let my truck sit at work for 8 hours on level-ish ground (more level then my driveway at home) and it'll fire right up, no problem.

 

Finally in this pic, it illustrates what I think is causing my problem. With fuel levels staying at 1/2 a tank BUT changing the slope of the truck to being parked up hill (in this case my driveway) you can see that now when the fuel sloshes to the back of the tank, it now exposes my much shorter OEM fuel return line to open air. What I'm thinking will solve this issue is simply extending my OEM fuel return line to a similar length as my FASS supply and return lines so that way it should never be exposed to open air in the fuel tank unless I was at an extreme angle with really low fuel in the tank.

 

Thoughts?

[Haggar]

Yep!!!!

 

nice work with paint!!!!!   I wanted to do that but didn't have the time.  (so I wrote a book.... in my mind that worked easier...) Yes that is exactly what happens with your short return line.  "one end" of the hose comes out of the water,  so air can go in and drains the whole thing.   Longer tube that keeps it submerged will solve a whole lot of that. 

 

Hag

[notlimah]

Thanks Hag, that's what I was thinking, glad someone else thinks the same so I know I'm not crazy! hahah

 

For now, I'm just going to deal with it since it's been getting pretty chilly around these parts, I don't feel like dropping the tank so I'll wait until things get warmed up. Plus, I want to see about finding an OEM style return tube so I can avoid running regular rubber fuel line.

[Haggar]

lol,  using me as a standard of crazy or not....  this may not be a good plan...  Leave it as we agree!  That way when those nice young men in their clean white coats come to take me away, they won't grab you too!

 

You could extend it with some stainless tubing if you needed, but I totally agree (and you guys are colder than us) the energy available to mess with this stuff is an inverse exponential of the temperature! 

 

Have a great one!

 

Hag

[dripley]

Thats what I would think is happening.  

[notlimah]

Just wanted to make note of this...

 

Tank was down to about a 1/4 and that's about as low as I like to run it so I figured I'd fill up on my way to work this morning. I noticed that my fuel pump didn't prime like it will usually do when the tank is more full. Also, my fuel pressure was moving more then normal, sometimes randomly independent of throttle input.

 

It's either one of two things.

 

1. Fuels sloshing around out of my fuel basket and causing pressures to vary slightly more then normal. They never dropped below 16-17 so it doesn't seem like it's sucking air, otherwise I feel I'd see a much bigger drop in pressure.

 

2. Fuels sloshing around enough to cover up the OEM fuel return line causing a pressure difference in the system which in turn is causing my fuel pressure to vary more then normal.

 

Either way, staying above a 1/4 tank isn't a problem for me as I'd prefer that anyways to avoid sucking up any bad stuff. The truck still starts fine on level ground and other then the pressure fluctuation, it's still within safe numbers. My fuel gauge is definitely off as I filled up at 1/4 tank today and was able to put a little over 27 gallons in the tank. At a 1/4 tank I should technically have 10 gallons remaining, when in fact I only had 7ish.

[IBMobile]

3 hours ago, notlimah said:

staying above a 1/4 tank isn't a problem for me as I'd prefer that anyways to avoid sucking up any bad stuff. 

Whether you have a full tank, ½ , ¼  or an empty tank sucking up bad stuff is unavoidable because the fuel pickup is on the bottom of the tank. 

My fuel gauge doesn't start to move from full until the truck has used about 10 gal.  When I have ¼ of a tank showing there is about 7-8 gal. left.   

[TFaoro]

4 hours ago, notlimah said:

Either way, staying above a 1/4 tank isn't a problem for me as I'd prefer that anyways to avoid sucking up any bad stuff. The truck still starts fine on level ground and other then the pressure fluctuation, it's still within safe numbers. My fuel gauge is definitely off as I filled up at 1/4 tank today and was able to put a little over 27 gallons in the tank. At a 1/4 tank I should technically have 10 gallons remaining, when in fact I only had 7ish.

I think long bed tanks are 34 gallons and short beds are 32 gallons. 

At a quarter you SHOULD have 8.5 for a long bed and 8 for a short bed. It's off by a bit, but not too bad. 

Mine doesn't move until about 6 gallons have been used, but after half a tank it seems to drop off pretty quickly. 

[Me78569]

same as mine, Typically I say 1 /2 tank is actually 1/3 tank, 3/4 is 2/3.  

 

 

 

[CSM]

A new sending unit is an easy install 

[notlimah]

20 minutes ago, TFaoro said:

I think long bed tanks are 34 gallons and short beds are 32 gallons. 

At a quarter you SHOULD have 8.5 for a long bed and 8 for a short bed. It's off by a bit, but not too bad. 

Mine doesn't move until about 6 gallons have been used, but after half a tank it seems to drop off pretty quickly. 

 

Oopps I got my numbers mixed up, but yes, long bed 34g tank. Meant that showing a 1/4 tank I would've expected to add about 25.5g and instead added 27.2g so instead of a 1/4 tank meaning I'm at 8.5g I was approximately 5.5g remaining with 1/4 indicated.

 

36 minutes ago, IBMobile said:

Whether you have a full tank, ½ , ¼  or an empty tank sucking up bad stuff is unavoidable because the fuel pickup is on the bottom of the tank. 

My fuel gauge doesn't start to move from full until the truck has used about 10 gal.  When I have ¼ of a tank showing there is about 7-8 gal. left.   

 

I agree, certain debris is unavoidable. I'm still running my fuel module with the screen installed in the bottom. Hopefully my FASS is doing it's job! Typically my gauge is pegged over full until right around 100 miles on the trip meter, then it starts to fall. Either way, my MPGs and bad!  lol

[dripley]

long beds have the 35 gallon tank and short beds have a 34 i believe. my long is definitely 35. My gauge is similar to the above 3/4 tank is a bout 2/3rds, half is about a 1/3rd left. Takes for ever to move off of full. When it was new it was the opposite. Used to be when it hit the low fuel light I could drive 100+ miles before filling. That all changed with the in tank pump install. Just went the other way. But it is always the same. It being accurate on gallons never bothered me. I still know how much fuel I have. Now when the light comes on I have maybe 50 miles to go, about 3 gallons. I really thought I was getting some good mileage after the pump change.