ALH air in fuel lines after sitting overnight

[J_dude]

Hello people,

So here’s the deal, I had an issue with my Jetta sputtering a bit when started after sitting overnight, after researching and discovering the thermo T issue, I decided to change over to a CAT filter on a Wix base. While I was at it I replaced the rubber fuel lines from the hard line to filter, from filter to IP, and the return from the IP to the return hard line. Also the injector return lines. Well, the problem persists, one way or another air is getting in the lines and causing rough starts and rough idle for a several seconds till it works the air out of the system. Where do I go from here?
I even tried a whole new filter and new base as well, with no change.
I also removed the filter and base (assembled) and pressure tested it but couldn’t find any leaks.

Any ideas appreciated.
Thanks

 

[Mongler98]

Check the check valves ag the tank pickup

 

[super1]

^^^
Do you see any visible leaks around the injection pump area?
The seals on the injection pump or prone to failure

also the head seal

 

[fatmobile]

So you replaced all the fuel lines with clear lines?
Where is the air coming from?
Sometimes I have to bend the lines so if it's coming from the pump input
it will get trapped there.

Is it coming out of the filter?
That's kinda normal and shouldn't cause a starting problem.

The little lines between the injectors can let air in when it sits.
Common cause of this problem on the old Rabbits
Clear line from the injectors to the pump?

 

[J_dude]

Check the check valves ag the tank pickup

I see there is something that looks like a check valve on the feed line at the tank pickup, it looks kind of like it is molded into the plastic hose, is it replaceable?

 

[Diesel Fumes]

Does the car start better or the same if you leave it plugged in for a few hours before cranking it? I have the same issues but they go away almost entirely if I have it plugged in with warm coolant before starting

 

[J_dude]

^^^
Do you see any visible leaks around the injection pump area?
The seals on the injection pump or prone to failure

also the head seal

I haven’t seen any fuel leaks around the injection pump, is it possible it could be internal or something, and not leak fuel but cause an air leak when it’s not running?

 

[J_dude]

So you replaced all the fuel lines with clear lines?
Where is the air coming from?
Sometimes I have to bend the lines so if it's coming from the pump input
it will get trapped there.

Is it coming out of the filter?
That's kinda normal and shouldn't cause a starting problem.

The little lines between the injectors can let air in when it sits.
Common cause of this problem on the old Rabbits
Clear line from the injectors to the pump?

Sorry I should have mentioned that too, I did put all clear lines on it for a while to see what was going on. Looks like I’m getting a few very small bubbles between the hard line and the filter and from the filter to the injection pump there’s some big bubbles. So it would appear as though it’s sucking those big bubbles in from the filter, but I pressure tested that and there’s no leaks...

 

[J_dude]

Does the car start better or the same if you leave it plugged in for a few hours before cranking it? I have the same issues but they go away almost entirely if I have it plugged in with warm coolant before starting

Well, being that the weather is getting colder these days, yes it does start better when plugged in, but this was happening even when it was warm out.

 

[fatmobile]

You didn't answer my question about a clear line from the injectors to the pump.
That's important if you are having hard cold start problems.

Have you hooked a vacuum gauge to the fuel input to see how hard the pump is pulling.
That would show if there is a fuel line restriction.

 

[J_dude]

You didn't answer my question about a clear line from the injectors to the pump.
That's important if you are having hard cold start problems.

Have you hooked a vacuum gauge to the fuel input to see how hard the pump is pulling.
That would show if there is a fuel line restriction.

Oh I didn’t think about clear lines on the injector returns, I will do that today

At the moment my vacuum gauge is broken but I will try to get that fixed and give it a try.

 

[jettawreck]

My 03 suddenly developed hard starts after sitting any length of time. After a bunch of pulling fuel with the MitiVac I finally found (even after removing and testing the fuel sender on the bench) the fuel sender outlet had a tiny crack where it's molded onto/into the top of the unit. Swapped it out with the one from the 2001 while I JB welded the hairline crack. It has since worked fine in the 2001 but I should replace it so as not to be stranded somewhere inconvienent (which is most anywhere).
The crack was so small as to be almost invisible and didn't leak air when I had it on the bench out of the car. When on the bench it had no pressure on the bend of the nipple and the crack would seal up. It was when I had put it back in the car and tested it right at the outlet that I noticed some residual fuel on the top of the sending unit was being pulled into the top cover. Ah ha!!

 

[fatmobile]

You don't need clear lines between all the injectors but
one clear line coming from the injectors to the pump
will show if air is being pulled into the pump on shutdown.

It sometimes takes a week of driving before all the air is purged after you open the fuel system.
It gets sent back to the tank and drawn back to the front for awhile.

 

[J_dude]

Ok, update, i added a check valve on the upstream side of the filter with no change to the symptoms. Then I was messing with the fuel line connections that the tank and BROKE the feed line at the little inline check valve! Well actually it broke one of the nipples off the check valve so I took it apart (destroyed it) to verify that it was indeed a check valve, because there didn’t seem to be any definite information online but that’s definitely what it is, although mine did not work anyway. At any rate, that happened while I was at work so I ran a temporary clear line from the tank to the filter just to get it home but ended up leaving it on for a week. While I had that line on I saw NO bubbles from tank to filter, however the issue still persists. I also put clear lines on the injector return lines and they still haven’t filled completely with fuel after a week of driving... lots of air bubbles at all times, could this be my issue?

This is getting frustrating..

Sorry if some of that didn’t make sense, it has been a long day lol

Thank you all for your input so far

 

[J_dude]

So I just read that through and I didn’t make it quite clear lol. I broke the factory check valve at the tank, not the one I installed at the filter.

 

[jettawreck]

Run a continuous line from the IP supply to the tank (or rig up a small remote tank but then you need a return line also) and run/drive it a bit and park over night. Eliminates all the check valves and connections. If the issue is resolved the problem is with the IP seals, not supply line, filter, etc.

 

[KLXD]

I once read, on these very Forums, that the "return lines" on the injectors do not flow fuel at all. Their funcfuncfunction is to allow the injector needles to lift. Without them there would be nowhere for the fuel behind the needle that is displaced by its rising to go resulting in a hydraulic lock up.

Makes sense when you consider the tolerance between the needles and bores.

 

[J_dude]

Run a continuous line from the IP supply to the tank (or rig up a small remote tank but then you need a return line also) and run/drive it a bit and park over night. Eliminates all the check valves and connections. If the issue is resolved the problem is with the IP seals, not supply line, filter, etc.

Ok this is kind of what I did, but I went from the tank to the filter, bypassing the factory feed line and thereby eliminating two more connections and possible leak points. I wouldn’t want to run it without the filter though, that’s not what you meant right? Also I’m assuming you meant to say if the issue is *not* resolved then it is the pump seals? I may have misunderstood.

Anyway I’m beginning to think I will have to change pump seals, but it doesn’t make sense to me, because I thought if the seals leak then there would be a fuel leak right?

 

[J_dude]

I once read, on these very Forums, that the "return lines" on the injectors do not flow fuel at all. Their funcfuncfunction is to allow the injector needles to lift. Without them there would be nowhere for the fuel behind the needle that is displaced by its rising to go resulting in a hydraulic lock up.

Makes sense when you consider the tolerance between the needles and bores.

Yeah that would make sense. The fuel in the lines doesn’t move unless you rev it up.

 

[KLXD]

You can have air leaks without fuel leaks. Could also be the shaft seal with leakage you don't see. Maybe that was mentioned above. I don't wanna bother looking but I don't want repeat them without due acknowledgement.

 

[J_dude]

You can have air leaks without fuel leaks. Could also be the shaft seal with leakage you don't see. Maybe that was mentioned above. I don't wanna bother looking but I don't want repeat them without due acknowledgement.

Ah I see, yeah shaft seal just occurred to me, I haven’t noticed anything in that area but I haven’t been looking I guess. Will have to check tomorrow

 

[jettawreck]

Ok this is kind of what I did, but I went from the tank to the filter, bypassing the factory feed line and thereby eliminating two more connections and possible leak points. I wouldn’t want to run it without the filter though, that’s not what you meant right? Also I’m assuming you meant to say if the issue is *not* resolved then it is the pump seals? I may have misunderstood.

Anyway I’m beginning to think I will have to change pump seals, but it doesn’t make sense to me, because I thought if the seals leak then there would be a fuel leak right?

For the short term "test" run I would eliminate the filter connections and often troublesome T fitting and bypass the filter. Won't be an issue short term.
More often than not air will leak in long before (if ever) fuel leaks out on the suction side of the pump sysytem.

 

[Figster]

You stated that you upgraded to a CAT filter. Did you install an o-ring on the threaded portion of the filter base before spinning the filter in place? This was an early error when the CAT filters were first being installed - they leak air around the threads and cause hard starting. I had this issue when I first installed mine ~18 years ago. The CAT filter itself doesn't come with an o-ring, IIRC, so you will need to find one that works.

I've switched to a Racor filter that includes a water separator bowl and have used that for the past ~ 15 years. The Racor is a direct replacement for the CAT filter. S3203 is the part number for the element, IIRC. The racor filter comes with a square cut ring that goes on the filter threads before installation.

 

[BobnOH]

If those clear lines on the returns is not fuel rated hose, like Viton, you'll want to replace those once you have your issue sorted.

 

[J_dude]

You stated that you upgraded to a CAT filter. Did you install an o-ring on the threaded portion of the filter base before spinning the filter in place? This was an early error when the CAT filters were first being installed - they leak air around the threads and cause hard starting. I had this issue when I first installed mine ~18 years ago. The CAT filter itself doesn't come with an o-ring, IIRC, so you will need to find one that works.

I've switched to a Racor filter that includes a water separator bowl and have used that for the past ~ 15 years. The Racor is a direct replacement for the CAT filter. S3203 is the part number for the element, IIRC. The racor filter comes with a square cut ring that goes on the filter threads before installation.

Well now that hadn’t occurred to me, I kind of assumed since it was sealed from outside it should be fine. However I did some reading and seems like that is also common on the CAT install on the duramax as well, so I pulled it apart today. Well, turns out this cheap WIX filter base I have doesnt really have a good sealing surface around/at the base of the threads but I put an o-ring in there anyway, so we will see in the morning if it actually helps anything I guess.
I think in the mean time I will order a seal kit for the IP

Funny thing, when I took the filter off today the car had just been running, for several minutes, but the filter wasn’t even half full of fuel.. I know it didn’t leak back to the tank because I have that check valve on that side of the filter. Hmm

 

[Figster]

How are you priming your fuel filter before starting the car?

When I change my filter, I use a vacuum pump (mityvac) on the outlet side of the filter to pull fuel through the filter and pre-fill it. Once I get a bubble free stream of fuel coming out of the filter, I quickly disconnect the vacuum hose and install the fuel line on to the injection pump hose fitting.

I've put the filter on dry once in the past, and it takes an enormous amount of engine cranking for the IP to pull fuel through the dry filter and get everything primed. Once I started priming the filter, the engine pretty much instantly starts right up after the filter change.

 

[jettawreck]

These possibilities are why I suggested the remote tank/line or a continuous line from tank to IP.
Eliminates the source(s) of air leaks down to the minimum.

 

[J_dude]

How are you priming your fuel filter before starting the car?

When I change my filter, I use a vacuum pump (mityvac) on the outlet side of the filter to pull fuel through the filter and pre-fill it. Once I get a bubble free stream of fuel coming out of the filter, I quickly disconnect the vacuum hose and install the fuel line on to the injection pump hose fitting.

I've put the filter on dry once in the past, and it takes an enormous amount of engine cranking for the IP to pull fuel through the dry filter and get everything primed. Once I started priming the filter, the engine pretty much instantly starts right up after the filter change.

Well initially when I swapped the last CAT filter and base for the new set, I just left the old setup in place and hooked up the return line from the IP to the feed line on the new filter base (uninstalled), and filled it that way, with the car running. Just have to shut the car off when the filter is full lol
Yes I know that’s not really the traditional method lol but I wanted to try it.
Anyway I took it apart and filled the filter last night, because I thought “well if the IP is pulling enough fuel to run, but not filling the filter, how would priming it with a vacuum pump do any better?”

 

[eddieleephd]

Often this is the head seal on the IP. Easy job to replace...

 

[J_dude]

Often this is the head seal on the IP. Easy job to replace...

Yes I think that is my next step. Interestingly enough, I put my old CAT filter and base back on (this one has no check valve) but I found and installed a square cut o-ring on the threaded part of the base like figster suggested and then primed the filter and drive it home. Now when I looked at it this morning there was mostly air in the clear line between the hard feed line and the filter, but when I fired it up it hardly sputtered at all and ran really quite smoothly right away. The very same thing happened this afternoon when leaving work, car had been sitting for over 8 hours and the fuel line was full of air (and normally it will sputter and rough idle till the air is gone just like it does after sitting overnight) but fired up right away and ran even better than the morning, so that o-ring seems to help on part of the issue at least. Although I will still do the pump seals because, well, it’s still getting air somewhere.

Anyway both times I started it today the frostheater had been plugged in so out of curiosity I’m going to see how it likes starting tomorrow without being plugged in..