suction leaks in fuel system

[GM Guy]

even if you sprayed ether around the fuel lines nothing would happen. this is not a gasser. if it is sucking air that bad, I doubt it would run.

the powerstroke issue that your buddy is talking about is the supply lines. either he is mis-informed, or is a fool, because from the factory, powerstrokes dont even HAVE return lines. the fuel dead-ends in the head, some feel this is why they are noisy and so to reduce noise, as well as hopefully increase power, mpg, smoothness in operation, etc, the aftermarket has developed a kit to install a return system. the powerstroke, for whatever reason, has multiple areas to disconnect the fuel line. at these disconnects, air can enter, but since air molecules are smaller that the molecules in diesel fuel, air gets in but fuel doesnt get out.

go ahead and post up what year of GM 6.5L diesel you have so we can help you, a few things are year specific.

all 6.5L diesels suck diesel out of the tank, down a line, to the lift pump (what is actually producing the suction to pull fuel from the tank) from here, the lift pump pushes fuel onward to the filter at 5-10 PSI (IIRC) fuel enters the filter housing, gets filtered, water seperated, heated if necessary, then into the line to the injection pump. the water drain is the t-fitting at the front of the motor. it receives the same PSI as anything else, so it is a great place to check PSI. drain it for a bit to ensure no crap will get into your guage, then test it. A Tee into the filter to IP line is great for telling you when the filter is clogged, but untill you get your leak fixed, PSI checking at the t-valve works fine.

the only thing return line related that can affect how a Stanadyne injecion pump operates is restriction. if you plug the return, the pump wont work right (I know this for certain on the mechanical units, electronic may not be affected) but as long as the return is free flowing, all is well. heck, the line could be off and you could piss diesel all over the ground and the IP wouldnt care.

 

[GM Guy]

even if you sprayed ether around the fuel lines nothing would happen. this is not a gasser. if it is sucking air that bad, I doubt it would run.

the powerstroke issue that your buddy is talking about is the supply lines. either he is mis-informed, or is a fool, because from the factory, powerstrokes dont even HAVE return lines. the fuel dead-ends in the head, some feel this is why they are noisy and so to reduce noise, as well as hopefully increase power, mpg, smoothness in operation, etc, the aftermarket has developed a kit to install a return system. the powerstroke, for whatever reason, has multiple areas to disconnect the fuel line. at these disconnects, air can enter, but since air molecules are smaller that the molecules in diesel fuel, air gets in but fuel doesnt get out.

go ahead and post up what year of GM 6.5L diesel you have so we can help you, a few things are year specific.

all 6.5L diesels suck diesel out of the tank, down a line, to the lift pump (what is actually producing the suction to pull fuel from the tank) from here, the lift pump pushes fuel onward to the filter at 5-10 PSI (IIRC) fuel enters the filter housing, gets filtered, water seperated, heated if necessary, then into the line to the injection pump. the water drain is the t-fitting at the front of the motor. it receives the same PSI as anything else, so it is a great place to check PSI. drain it for a bit to ensure no crap will get into your guage, then test it. A Tee into the filter to IP line is great for telling you when the filter is clogged, but untill you get your leak fixed, PSI checking at the t-valve works fine.

the only thing return line related that can affect how a Stanadyne injecion pump operates is restriction. if you plug the return, the pump wont work right (I know this for certain on the mechanical units, electronic may not be affected) but as long as the return is free flowing, all is well. heck, the line could be off and you could piss diesel all over the ground and the IP wouldnt care.

 

[nealpellecchia]

even if you sprayed ether around the fuel lines nothing would happen. this is not a gasser. if it is sucking air that bad, I doubt it would run.

the powerstroke issue that your buddy is talking about is the supply lines. either he is mis-informed, or is a fool, because from the factory, powerstrokes dont even HAVE return lines. the fuel dead-ends in the head, some feel this is why they are noisy and so to reduce noise, as well as hopefully increase power, mpg, smoothness in operation, etc, the aftermarket has developed a kit to install a return system. the powerstroke, for whatever reason, has multiple areas to disconnect the fuel line. at these disconnects, air can enter, but since air molecules are smaller that the molecules in diesel fuel, air gets in but fuel doesnt get out.

go ahead and post up what year of GM 6.5L diesel you have so we can help you, a few things are year specific.

all 6.5L diesels suck diesel out of the tank, down a line, to the lift pump (what is actually producing the suction to pull fuel from the tank) from here, the lift pump pushes fuel onward to the filter at 5-10 PSI (IIRC) fuel enters the filter housing, gets filtered, water seperated, heated if necessary, then into the line to the injection pump. the water drain is the t-fitting at the front of the motor. it receives the same PSI as anything else, so it is a great place to check PSI. drain it for a bit to ensure no crap will get into your guage, then test it. A Tee into the filter to IP line is great for telling you when the filter is clogged, but untill you get your leak fixed, PSI checking at the t-valve works fine.

the only thing return line related that can affect how a Stanadyne injecion pump operates is restriction. if you plug the return, the pump wont work right (I know this for certain on the mechanical units, electronic may not be affected) but as long as the return is free flowing, all is well. heck, the line could be off and you could piss diesel all over the ground and the IP wouldnt care.

I agree. 1993 6.5 turbo diesel pick up heavy duty 4 wheel drive automatic. I was gonna next remove the filter cannister and splice in a temporary clear fuel filter. I can look for air bubbles and see if the problem goes away. I'm told the canisters leak a lot. Again, it runs great after I get it started and clear out the air at 3,000 rpm for 20 to 30 seconds... Can it have a plugged return line if it runs good? but I have occasional high idle, poor advance, smoke out of tail pipe going down hill at cruseing speed.

 

[bison]

There is no need to take the filter manager out.
Read my first post again,it says how to check for airbubbles in the system.

 

[nealpellecchia]

There is no need to take the filter manager out.
Read my first post again,it says how to check for airbubbles in the system.

I hoped you would say that and I've delayed from yesterday. I know that I have air in the system because of the way it's behaving and then runs well. Once you know that their is air in the system it is very hard to find where it is coming in. I don't want to have to drop the tank and take off those lines and put pressure on the input line while blocking the return line as the book tells you to do. Plus I can't get that return hose off on top. It is really tight! A good source says that the fuel cannister is a common source of this kind of problem and that their is even a replacement one that the dealer wants 200.00 for. So, I can check all the hose fittings to the cannister while removing them and when taking it out of the way I can reach under and check that hard to reach fitting right under the middle of the intake manifold. So why not bypass it for the moment and see how it runs with out it? But I don't want particles to get in the pump so I'll add a 2.00 filter in line. Then I can pressure test the cannister and look for leaks at the o rings more closely.

You said that with the year model you might know of some leak/ problem locations?

 

[ak diesel driver]

the FFM on the older trucks ie 84 or so were the ones that had FFM leaks newer ones don't have the issues older ones did. to find an air leak start replacing the rubber lines with clear tubing until you find where the air originates from. It would be REALLY helpful if we knew what we were working on.

 

[bison]

Frankly i think you have a suction air leak pre LP.(rusted out line or bad rubber hose or bad 0 ring on the hose or LP connection or something like that).
i you have some vacuum in the tank a fuel leak pre LP might not even show till the pressure is equalized. Don't rely on the LP checkvalve to hold pressure on that end cause they all leak(even when new.
Any problem after the LP should be leaking fuel with the LP running..
Air could get in the system post LP when the LP can't keep up with the demand or you got a plugged fuel pickup sock
A clear tube(best to leave it on permanently) on the IP return line lets you see if there is air passing trough with engine running or a leak back on the supply or return side after engine shutdown cause it'll fill with air

 

[nealpellecchia]

Frankly i think you have a suction air leak pre LP.(rusted out line or bad rubber hose or bad 0 ring on the hose or LP connection or something like that).
i you have some vacuum in the tank a fuel leak pre LP might not even show till the pressure is equalized. Don't rely on the LP checkvalve to hold pressure on that end cause they all leak(even when new.
Any problem after the LP should be leaking fuel with the LP running..
Air could get in the system post LP when the LP can't keep up with the demand or you got a plugged fuel pickup sock
A clear tube(best to leave it on permanently) on the IP return line lets you see if there is air passing trough with engine running or a leak back on the supply or return side after engine shutdown cause it'll fill with air

very good. good info. I think i'm seeing a bigger and thinner puddle under the engine on the ground where I have my usual oil leak. another problem. it is right under the back of the engine. maybe a lot of the wetness that has been is fuel going down the back of the engine around the bell housing area. and when i replaced the filter recently it was strikingly only half dirty. as if the fuel level wasn't rising all the way up. either low fuel pressure or a leak. no noticeable smell though! i had a lot of smell when the end of the drain line became dilapidated near the thermostat housing several years ago, heat I thought. I just shortened that line cutting it back to good hose. so, no smell of fuel have i noticed. i did put some air pressure into the tank the other day trying to raise the fuel pressure and force a leak. maybe i did! and it's leaking more past the o ring seals in the filter housing. i also looked up on top of the fuel tank sender with a flashlight and a mirror and thought i saw rust up there. so i agree with all your thoughts thank you. oh and the part about a leaky return line bleeding down the pressure is what my boat mechanic said about fords he's worked on with similar symptoms.

 

[nealpellecchia]

Frankly i think you have a suction air leak pre LP.(rusted out line or bad rubber hose or bad 0 ring on the hose or LP connection or something like that).
i you have some vacuum in the tank a fuel leak pre LP might not even show till the pressure is equalized. Don't rely on the LP checkvalve to hold pressure on that end cause they all leak(even when new.
Any problem after the LP should be leaking fuel with the LP running..
Air could get in the system post LP when the LP can't keep up with the demand or you got a plugged fuel pickup sock
A clear tube(best to leave it on permanently) on the IP return line lets you see if there is air passing trough with engine running or a leak back on the supply or return side after engine shutdown cause it'll fill with air

ok, i fixed it. i unbolted the filter housing, moved it around a little bit and then removed the input line. no fuel comes out but i see that the id is much bigger than my bypass kit. Also the clamp seems pretty loose...i had already had it off from when i first tightened them all down a couple of weeks ago. i tell myself that at least i started doing something. I put it back together and force myself to finally cut off that return hose on the top. It would be progress to get that done to and look for air bubbles tomorrow even though i'm 99% sue that i got air in the lines. when i do i can hear gurgling down the lines...a bleed down i presume.

The next day i'm planning on taking the gas tank down myself...and so i decide ti start it and have fun looking for air bubbles instead of the dirty tank removal job. I have been forced to start it and rev the engine very high until the air in the lines clear out...not very long but i don't like waking my baby up like that. So this time i decide to just let it wake up slowly , stall a few times and bleed the air off the filter in a more calm procedure. The glow plug light goes out i start it and it runs perfectly! no stalling. I get out to look at my clear hose stuck on with no clamps and it is clear as a whistle! signed, Neal's Diesel repair.

 

[JiFaire]

Glad you got it fixed. So you're saying it wasn't the return line, like your Ford mechanic said? Glad you didn't get bogged down looking for leaks in the non-pressure side of the system with ether... methodical troubleshooting always solves the problem, sooner or later.

When you get a little time, it wouldn't be a bad idea for you to methodically go through the troubleshooting checklist found in my signature, for both basic maintenance purposes, and so you have some ready-to-use clear answers for the guys here if you ever have another problem to solve. This thread is a bag of snakes, with conflicting questions, ideas, and notions... you might have had this solved a lot faster if the guys had the information they needed right off the bat.

Also, Take a minute and fill out your signature, ok? It really helps to know what we're looking at.

 

[nealpellecchia]

Glad you got it fixed. So you're saying it wasn't the return line, like your Ford mechanic said? Glad you didn't get bogged down looking for leaks in the non-pressure side of the system with ether... methodical troubleshooting always solves the problem, sooner or later.

When you get a little time, it wouldn't be a bad idea for you to methodically go through the troubleshooting checklist found in my signature, for both basic maintenance purposes, and so you have some ready-to-use clear answers for the guys here if you ever have another problem to solve. This thread is a bag of snakes, with conflicting questions, ideas, and notions... you might have had this solved a lot faster if the guys had the information they needed right off the bat.

Also, Take a minute and fill out your signature, ok? It really helps to know what we're looking at.

I'm saying I'm not sure. But I heard a bleed down on the return side when I removed the return hose. The old one was hard and dry. Had to! cut it off. But you say a return line hose is not necessary. Even over night? I basically giggled the filter housing... I had the problem with a definite tight clamp on the fuel input line at filter. I"m just honestly describing all the evidence. And I think it's the clear new return hose. Diesel guy thought so saying that old you can't see a crack.

 

[JiFaire]

The return line is just what it sounds like... it returns excess fuel to the tank. NOTHING - including fuel or air - goes from the return line to the injectors; an air leak in the return line will NOT affect the injection event at all.

If you have air in the lines that is making your truck run rough, the air is in the pressure side. By putting the clear hose in the return line, you will be able to see air bubbles that are coming through the pressure side of the system, as they congregate once they get past the injectors and into the non-pressure side; you can also put the clear line in the pressure side of the system, just ahead of the injection pump, but it's more work, harder to see, and risks introducing another leak into the system ahead of the IP.

Simon and the others are most likely correct; leaks in the pressure side happen most often between the tank and the Lift Pump (mounted on the frame), as that's the only usual 'suction' part of the system. If your Lift Pump is working correctly, everything from there to the Fuel Filter Manager, then to the Injection Pump is under pressure; cracks will result in fuel leaking out of the system, not air leaking into the system. Where air gets into the system (as was correctly pointed out) is when the Lift Pump is shut off, and the fuel pressure in the lines/FFM drops, which can result in air 'siphoning' into the FFM...

Seals in the FFM are also a big culprit in this scenario, as is improper installation of the new fuel filter. Did you say that you had the FFM apart a few weeks ago? Was this before or after the 'air in the system' symptoms appeared?

As for using ether or various other sprays, even if they mixed into the fuel on the pressure side of the system, they would have no effect. What you're describing is a technique used by gas mechanics to check for vacuum leaks - because the ether gets 'sucked' into the system with the AIR, not with the fuel. Diesels work the same way... if you spray ether near your intake while idling, your truck will react ... but not because you found an air leak in the fuel system.

 

[nealpellecchia]

The return line is just what it sounds like... it returns excess fuel to the tank. NOTHING - including fuel or air - goes from the return line to the injectors; an air leak in the return line will NOT affect the injection event at all.

If you have air in the lines that is making your truck run rough, the air is in the pressure side. By putting the clear hose in the return line, you will be able to see air bubbles that are coming through the pressure side of the system, as they congregate once they get past the injectors and into the non-pressure side; you can also put the clear line in the pressure side of the system, just ahead of the injection pump, but it's more work, harder to see, and risks introducing another leak into the system ahead of the IP.

Simon and the others are most likely correct; leaks in the pressure side happen most often between the tank and the Lift Pump (mounted on the frame), as that's the only usual 'suction' part of the system. If your Lift Pump is working correctly, everything from there to the Fuel Filter Manager, then to the Injection Pump is under pressure; cracks will result in fuel leaking out of the system, not air leaking into the system. Where air gets into the system (as was correctly pointed out) is when the Lift Pump is shut off, and the fuel pressure in the lines/FFM drops, which can result in air 'siphoning' into the FFM...

Seals in the FFM are also a big culprit in this scenario, as is improper installation of the new fuel filter. Did you say that you had the FFM apart a few weeks ago? Was this before or after the 'air in the system' symptoms appeared?

As for using ether or various other sprays, even if they mixed into the fuel on the pressure side of the system, they would have no effect. What you're describing is a technique used by gas mechanics to check for vacuum leaks - because the ether gets 'sucked' into the system with the AIR, not with the fuel. Diesels work the same way... if you spray ether near your intake while idling, your truck will react ... but not because you found an air leak in the fuel system.

I tested gas engines many times like this...on diesel i think you can get a reaction but a little delayed.

it seems that the return hose was leaking. again when i pul;led the hose i heard a siphon going away

 

[JiFaire]

I tested gas engines many times like this...on diesel i think you can get a reaction but a little delayed.

Nope.


I'm not doubting that you have tested gas engines like this, but remember, this ain't a gas engine. On the fuel side - between the tank and the Injection pump - there is between 0 and 8 PSI. The only way you get your ether spray into the fuel is if there is suction to pull it in, and if you have suction in that line, you have more issues than a leak.

Between the Injection pump and the injectors, there is HUGE pressure, no way is ether getting into the fuel on that part of the circuit.

The reason this works on gassers is because of the throttle plate under the carb/TBI... the engine develops vacuum to suck the fuel-air mix in. Spraying ether around the base of the carb/TBI, intake manifold gaskets, EGR, etc can suck ether into the cylinders, causes a change in idle because you're getting more fuel into the cylinder. Spraying ether around the fuel lines on a gasser won't do anything, either.

Ether detects air intake leaks. Period.

it seems that the return hose was leaking. again when i pul;led the hose i heard a siphon going away

Here's how the return circuit works: when your IP sends a surge of pressure to the Injectors, they 'POP', letting fuel spray into the cylinder. This is a very high-pressure event, even in our old tubs. When the injector snaps shut, the fuel trapped in the injector has to go somewhere, so a it goes into the return circuit. (look at your injectors... you have a big steel line with high pressure, coming from the IP, and a little rubber hose, which is just pushed onto the little nipples on the injector. That hose runs from injector to injector, collecting the little bits of unused fuel, and returns them to the tank.

If you had NO return lines, that little bit of unused fuel would just leak out... no fuel from the return line goes back to the cylinders. Ever.

Your Ford guy is wrong. Sorry to be blunt. Leaky Return lines on a 6.5 are different than what he may be used to.

If you pull off a return line and spray ether straight into it, your idle will NOT change. It can't. The ether will possibly return to the fuel tank, mix with your diesel, and make its way back to the Injection Pump, but unless you spray about 5 cans into the return line, it will do nothing to your engine.

 

[bison]

And that is that

 

[nealpellecchia]

Nope.


I'm not doubting that you have tested gas engines like this, but remember, this ain't a gas engine. On the fuel side - between the tank and the Injection pump - there is between 0 and 8 PSI. The only way you get your ether spray into the fuel is if there is suction to pull it in, and if you have suction in that line, you have more issues than a leak.

Between the Injection pump and the injectors, there is HUGE pressure, no way is ether getting into the fuel on that part of the circuit.

The reason this works on gassers is because of the throttle plate under the carb/TBI... the engine develops vacuum to suck the fuel-air mix in. Spraying ether around the base of the carb/TBI, intake manifold gaskets, EGR, etc can suck ether into the cylinders, causes a change in idle because you're getting more fuel into the cylinder. Spraying ether around the fuel lines on a gasser won't do anything, either.

Ether detects air intake leaks. Period.



Here's how the return circuit works: when your IP sends a surge of pressure to the Injectors, they 'POP', letting fuel spray into the cylinder. This is a very high-pressure event, even in our old tubs. When the injector snaps shut, the fuel trapped in the injector has to go somewhere, so a it goes into the return circuit. (look at your injectors... you have a big steel line with high pressure, coming from the IP, and a little rubber hose, which is just pushed onto the little nipples on the injector. That hose runs from injector to injector, collecting the little bits of unused fuel, and returns them to the tank.

If you had NO return lines, that little bit of unused fuel would just leak out... no fuel from the return line goes back to the cylinders. Ever.

Your Ford guy is wrong. Sorry to be blunt. Leaky Return lines on a 6.5 are different than what he may be used to.

If you pull off a return line and spray ether straight into it, your idle will NOT change. It can't. The ether will possibly return to the fuel tank, mix with your diesel, and make its way back to the Injection Pump, but unless you spray about 5 cans into the return line, it will do nothing to your engine.

i didn't spray on a return line. Right that'll at best send some ether to the fuel tank to mix with a lot of gas. I think that if the leak is big enough...suction.. the ether is powerful enough to mix with the incoming fuel and cause a rpm change for a second. I didn't bother to spray any thing but water. mechanics said that they're taught to use soapy water and lees volatile sprays.

So the queston remains; what is fixed on this truck? did pulling the filter housing around a little bit and taking off and putting back on the fuel input accidentally solve the leak? Or is a check ball suddenly working in the pump to stop the pressure bleed down? or is the replaced return line holding pressure so it prevents the pressure from bleeding down on the other side of the loop? tell me about this check ball. does it block the ip from the return when the engine is shut off? cause if it doesn't or it ain't working ...

they mention a check ball in the book but somewhere else it said something else that led me not to worry. remember, the problem started only hot and then it did it cold as well and was getting worse.

 

[nealpellecchia]

no fuel ever goes back to the cyl's... what about the stuff that goes back to the tank.

 

[nealpellecchia]

no fuel ever goes back to the cyl's... what about the stuff that goes back to the tank.

meaning that the syphon effect might go through the fuel in the tank on back to the supply line. well i just changed that clear hose with a better one. what i did was based on what i observed. when i first changed the hose there was no fuel in it. truck had stood over night. pulled it right off! no mess. when i just saw fuel in the line i very gently wiggled the hose to let a little air in at a time while the fuel level fell back into the tank. i didn't spill a drop. and the truck started hard a minute later not overnight, and i had to clear out some air that WAS now in the supply line with some rpm's to keep it running.

 

[JiFaire]

You need to flow-test your lift pump. When your engine is idling, and you open the water drain (brass t-handle), what happens?

The troubleshooting checklist linked in my signature might also be helpful. As would the signature link. Further information is also found by following the link to the 6.5 Technical Reference Library.