Air in Injector overflow lines?

[moclovflop]

Hi Guys,

Working with my first diesel, a Mk1 caddy, and am learning as much as possible just by lurking. But had a questions about some air in the lines...

Background: car is very well maintained, low (145k) miles with lots of maintenance done in the past year.

Specifically:
-tank dropped and cleaned
-new fuel filter and some lines.
-clear lines from/to filter, tank, and injection pump.
-cleaned, sealed, and timed injection pump
-rebuilt injectors
...and more.

Now, I've been daily driving the car for a few weeks and it's been mostly flawless. However yesterday after work, it wouldn't start and after checking, it was obvious that it had lost all it's prime and there was lots of air in both return and inlet fuel lines. After checking all the junctions on the fuel lines and whatnot, there was no visible fuel leak and no cracks and no sign of anything loose. I gave a good twist to the fuel filter to ensure it was tight and opened the drain on the filter to ensure it had fuel (it did).

I siphoned as much fuel in the inlet as i could and reattached it and tried cranking it again and after about 10 seconds it finally caught and sputtered to life. Had to use the cold start and give it some gas, but it leveled off quickly and didn't need my help after that.

While it was idling I watched the lines as the bubbles went from large, to small, to foamy (ultra small) to non-existent on the return line. The inlet was full of fuel and no bubbles once it was started.

However, even once all the in/out lines were full of fuel and had no bubbles, I noticed that the overflow hoses between injectors had nearly no fuel in them, more air than anything.

This is my concern: What would cause those lines to be empty? Are they not sealing? did they cause the loose of prime? They should be full when idling, right?

Went out this morning and the clear lines on the feed/out were fully primed and had no bubbles, so there was no air overnight.

So long story short: Lost prime/lots of bubbles. Eventually got it started and everything filled correctly except the overflow lines between injectors. Didn't lose prime/get air before or after this issue (only happened once so far). No issues after driving it home and letting it sit over night. No power loss, no stumbling.

Ideas? I'm thinking one of the lines work themselves loose and while I was trying to figure out what was wrong I was checking all the clear lines and maybe resealed it?

What causes air in the OUT line? And why would the bubbles disappear as it's idling? If there was a leak wouldn't it still be sucking in air?

[vanbcguy]

The small lines on the injectors actually should have next to no fuel in them, especially if your injectors are in good condition. They are there to provide a pathway back to the tank for any fuel that leaks around the nozzle inside the injector body. Not having any fuel in them is a good thing!

It is normal for it to take a while to get all the air out of the injection pump - everything inside it is spinning around, so any air that is present gets thrashed in to the fuel pretty thoroughly. The behavior you saw with the bubbles reducing in size and eventually stopping is consistent with an IP that was full of air.

Next time you shut the car off open the hood and watch for fuel movement back down the lines. The most common cause of the symptoms you describe is probably a bad input shaft seal on the pump given you didn't see any bubbles in the inlet line and you aren't seeing any leaks. If that is the case you will likely see air coming from the IP and going back down the supply line shortly after shutoff, with the return line doing the same thing not long after.

[moclovflop]

Thanks for the reply. Sorry for the delay, I missed the notice and it never did it again after that first time....

Until today.

What would cause sporadic loss of prime and cause air to get in the lines? I have been checking it over the past week and it never had any air bubbles or anything wired, and then out of no where it happens.

Thoughts? Think it would still be the input shaft seal? Loose line? Bad filter?

Thanks again

[vanbcguy]

It's hard to say really, especially from here!

I like the input shaft seal for this since it has a spinning shaft in it - it is essentially getting disturbed every time the engine runs which would explain the inconsistent behavior. If it were a cracked line or something similar it would happen every time.

[moclovflop]

That's true. Keyboard diagnostics are hard at best.

So how hard is that repair? And are you thinking that it's "landing" on a bad spot everyone and a while which is causing the air to get in?

[vanbcguy]

More or less yeah, that would be my theory.

The shaft seal itself isn't TOO bad, the pump has to be removed so it is a good time to plan for a timing belt job as well. The big question though will be around how it failed.

The pump input shaft rides in a bushing in the pump. If the engine has been run with the timing belt over tightened the bushing gets worn. If the bushing gets worn the shaft seal gets worn since the shaft is no longer straight. If the bushing is bad enough a new seal won't last long - make sure you try rocking the IP pulley with the timing belt removed, you don't want much side to side movement.

[moclovflop]

Bummer, the timing belt was just done not more than 1500 miles ago.

Did it again this morning, so it's getting worse obviously.

Some new symptoms...

-Once the majority of the bubbles have cleared after I'm able to start it, there are little "puffs" of dense air that I can see in the return line. I'm betting this is still in regards to the pumps clearing out the air as its going....?
-Audible sucking or squishing sound while warming up around the pump, but might be coming from somewhere nearby. It's slow, like once or twice a second, so it's slower than the motor's RPM.
-MPG Seems to not be great.

Is it possible it could be anything besides the input shaft seal? Not really looking to tear everything apart.

How about the solenoid? Any chance it's as simple as that being stuck?

Would the easy-way-out of an inline fuel pump help me here? Or am I up a creek since it seems to be in the pump?

Bought a mityvac to try to get the pump primed the next time this happens to cut wear on the starter.

Thanks again for the help. Again, I know it's hard via the forums. Might need to find my local guru and ask for some advise.

[srgtlord]

Sounds like you overtightened the timing belt the first time around.  Ive had this issue before. You might get lucky if you replace the front shaft seal and pack it full of vasoline like I did.  Ive put about 5000 miles on since I replaced the seal.

[srgtlord]

Almost forgot to mention that I neded to realign the injection pump to keep it from falling off the pullies...

[vanbcguy]

Bummer, the timing belt was just done not more than 1500 miles ago.

Did it again this morning, so it's getting worse obviously.

Some new symptoms...

-Once the majority of the bubbles have cleared after I'm able to start it, there are little "puffs" of dense air that I can see in the return line. I'm betting this is still in regards to the pumps clearing out the air as its going....?
-Audible sucking or squishing sound while warming up around the pump, but might be coming from somewhere nearby. It's slow, like once or twice a second, so it's slower than the motor's RPM.
-MPG Seems to not be great.

Is it possible it could be anything besides the input shaft seal? Not really looking to tear everything apart.

How about the solenoid? Any chance it's as simple as that being stuck?

Would the easy-way-out of an inline fuel pump help me here? Or am I up a creek since it seems to be in the pump?

Bought a mityvac to try to get the pump primed the next time this happens to cut wear on the starter.

Thanks again for the help. Again, I know it's hard via the forums. Might need to find my local guru and ask for some advise.

There are other possibilities for sure - there's a multitude of ways for air to get into the system and the injection pump is the highest point, meaning any air that gets in anywhere will go there.  That's why I'd try and catch it in action if at all possible after a shutdown.  I'm also HEAVILY relying on your mention that you do not see any air bubbles going in to the pump during operation - the fuel filter is a super common place for air to get in for instance, though you'd definitely see bubbles going from the filter to the pump if that was the case.

Definitely not the solenoid - it does not have any way to let air in.  It only controls fuel flowing from the pressurized part of the pump body to the actual high pressure pump head - if it were sticking or otherwise malfunctioning it would cause severe running issues.

All the rest of the pump seals are pressurized when the pump is spinning, so if any of them were bad you'd have a noticeable leak.

ONE other possibility could be the pump inlet banjo, worth checking first since you can get at it without disturbing anything else.  It's right at the pump and under vacuum too.

You do mention that the timing belt was done just 1500 miles ago - how did you tighten it?  Any chance you went overboard?  If it is too tight it will destroy the intermediate shaft bearing quickly too, which is very difficult to repair without pulling the engine from the car.

[moclovflop]

You are offering some great advise, thanks.

Unfortunately I didn't do the TB, it was the previous owner so I've asked him for his input. Will let you guys know once I hear.

I will pull the TB cover off ASAP so I can see if there's a visible leak. I also might replace the filter just to be sure it's not the issue, and tighten the drain on the filter as well to rule it out.

As for the banjo bolts, where are you guys getting the copper washers? If I check it, I want to make sure it's sealing right when it goes back on. Same thing for the OUT bolt.

And I still stand by the fact that I'm not seeing any air bubbles in the inlet line while running. And I noticed today after shutting it off that there were some in the outlet.

Also noticed that there is air in both the inlet and outlet lines after it's been sitting. Is that possible if there's a leak in a line somewhere? Or only if it's a bad seal on the pump?

Really hoping it's not the shaft seal.


Thanks again for the help, I've been searching and reading everything I can so that it's not all up to you, but I am still new so this helps a ton.

[vanbcguy]

OK - try twisting the timing belt, you should be able to turn it about 45 degrees with just your finger and thumb. If it won't twist that far then it is too tight. A lot of people screw up with that - they think it is like a v-belt where it needs to be quite tight. Really it needs to be just tight enough that it isn't flapping around - there is no stretch in it at all so the weakest bearings (the intermediate shaft and the injection pump) get trashed if it has a lot of tension in it.

The copper washers can be annealed by heating them with a torch till they are glowing, obviously nowhere near the pump or any fuel. They usually will seal well after that - the copper softens up again. Alternatively any shop that services smaller Cummins diesels will have them, the VE pump is not at all unique to Volkswagen. Lots of trucks running around out there with the same Bosch injection system.

[moclovflop]

Thanks for that.

Heard back from the Previous owner and he confirmed it was done to the 12-13mm spec that is called out in the repair books. I hand checked the deflection and it was about what you noted, no less than 45 deg of movement. So it doesn't seem over tight.

I also noticed that since sitting for the past 4 hours, there's no air in the system.

But while messing with the lines, I noticed the #1 injector overflow plug was pretty ugly. So I poked it a little bit and as I was doing it, air started flowing through the overflow lines and into the OUT bolt and the out line.

If this is the issue, that would cause everything, right?

Needless to say, I'll be grabbing a silicon block off nipple on the way home tonight to replace it. Or Will the diesel destroy silicon? Anything available over the counter to use?

Fingers crossed that it's just this.

[vanbcguy]

Yes, that could definitely be the cause of everything!!

I think silicone will be OK but I'm not certain. The actual proper block off caps are available too - again most diesel shops should have them. VW dealers probably do too - the same cap was used all the way through 2003.

[TimpanogosSlim]

The copper washers can be annealed by heating them with a torch till they are glowing, obviously nowhere near the pump or any fuel. They usually will seal well after that - the copper softens up again. Alternatively any shop that services smaller Cummins diesels will have them, the VE pump is not at all unique to Volkswagen. Lots of trucks running around out there with the same Bosch injection system.

One of the local car nerds i know was asking for help timing the VE pump on his cummins and told me "I think the technology is different" when i offered to loan him my timing adapter. ah well. his loss. (it's not different and i have the 'universal' adapter with several bushings to support different size ports)

auto parts stores seem to only carry packs of mixed sizes of copper washers which are supposed to be a great help if you are in a bind but i spent a lot of time late one night filing one down to fit inside the high pressure pump on my (gasser) mk5 because it was the closest in the assortment.

I've made a habit of figuring out what sizes i need and buying them in bulk online. But annealing them myself sounds like a great idea - if only i hadn't gotten too cavalier about leaving tools outside in the summer. I think some teenager walked off with my propane torch.