Author Topic: bleeding air out of fuel lines on AAZ  (Read 7011 times)

December 07, 2015, 11:12:16 pm

Sauerkraut

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bleeding air out of fuel lines on AAZ
« on: December 07, 2015, 11:12:16 pm »
I'm having a difficult time bleeding the air out of my fuel lines on my AAZ, I've been having an intermittent miss at idle (that seems more constant when cold) that I cannot figure out, I've since replaced the fuel filter, "T" fitting, added clamps to existing lines and replaced the "soft" hosing between injectors with clear hosing, the existing hose was dry and brittle.

it runs noticeably better but still feels quite underpowered, for the life of me I cannot bleed the excess air out of the lines from each injector, I've run the vehicle and cracked each hard line on top of each injector to have diesel spits out but the air pockets will not go away and remain.

here are two photos of the air pockets that I cannot get rid of in the clear hosing, what is the proper way to bleed the system? I have a feeling I'm doing something wrong and I cannot find my answer searching.

help!







Reply #1December 08, 2015, 12:51:14 am

zuhandenheit

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Re: bleeding air out of fuel lines on AAZ
« Reply #1 on: December 08, 2015, 12:51:14 am »
First thing: Do you have a clear line running from the filter to the pump? If so, are there bubbles in it?

I've had the line develop a very small crack -- too small to see, and it didn't leak -- but enough to let air in.

Reply #2December 08, 2015, 12:53:01 am

Sauerkraut

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Re: bleeding air out of fuel lines on AAZ
« Reply #2 on: December 08, 2015, 12:53:01 am »
I do have clear line going to the IP from the fuel filter, there are no bubbles going to the pump, that issue was fixed with changing the fuel filter. when it acts up I will notice a lot of bubbles coming out of the pump though.

I've replaced all the soft/rubber lines and added clamps to ensure they are tight.

Reply #3December 08, 2015, 02:04:05 am

zuhandenheit

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Re: bleeding air out of fuel lines on AAZ
« Reply #3 on: December 08, 2015, 02:04:05 am »
If the IP has a leak, it can lose its prime when it sits. But this would affect only starting and the first few minutes it's running, I think.

I only have a little experience, and so probably can't offer any more help. I'm sure that the much more knowledgeable people will chime in.

I can tell you that I've had to prime my system many times, and it's always been fairly straightforward, although not necessarily easy. When I've had the pump off, I start by either using a vacuum and bottle rig I've made to draw fuel through the return port on the pump. After that, or if I'm priming after just replacing a fuel line or something, I just crack the nuts and crank it until fuel comes out.

Once you're able to get it to start, it should take care of itself.

I really am not sure if air in the return lines is normal or not. I wouldn't think so, but I've never had clear lines, and I haven't heard anything one way or another.

Reply #4December 08, 2015, 09:00:13 am

TylerDurden

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Re: bleeding air out of fuel lines on AAZ
« Reply #4 on: December 08, 2015, 09:00:13 am »
Air in the small injector return lines is inconsequential. No need to bleed.

However, if they are letting in air when the engine sits (check that little plug in the last injector line) the air can be drawn back into the IP and it can interfere with starting/running until the air in the IP is purged.

Reply #5December 08, 2015, 01:39:03 pm

Sauerkraut

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Re: bleeding air out of fuel lines on AAZ
« Reply #5 on: December 08, 2015, 01:39:03 pm »
the injection pump nor the lines let air into the system when it sits, when the car is idling and I pull the throttle the fuel in the return lines seems to be sucked into the injectors, I'm uncertain if when I boost the engine if it's potentially running out of fuel because of this. the car seems abnormally slow and I cannot see what the lines are doing when I am driving. I thought that having the fuel react the way it is when the throttle is pulled, that it may pull fuel from the return line off of the side of the injection pump under higher loads, but these bubbles would be consumed by the injectors/pump before any additional fueling since it appeared to not be "bled".

the car starts without issue with minimal cranking, I normally cycle the glow plugs a couple times before hand, it gives a puff and idles like a champ, I just notice a miss at idle that's constant when the vehicle is cold, and intermittent when it's at operating temperature.

Reply #6December 09, 2015, 01:58:06 pm

Sauerkraut

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Re: bleeding air out of fuel lines on AAZ
« Reply #6 on: December 09, 2015, 01:58:06 pm »
does anyone by chance have the detailed sequence on how to bleed the system properly? possibly from the Bently manual?

is there anything on the injection pump to help bleed the system?

Reply #7December 09, 2015, 04:52:19 pm

wolf_walker

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Re: bleeding air out of fuel lines on AAZ
« Reply #7 on: December 09, 2015, 04:52:19 pm »
It really shouldn't be that complex, I pull a vacuum on the return outlet of the pump till fuel comes out, if the system is totally dry I might open the injector fittings at the injector while someone
cranks till fuel comes out, then I crank till it starts which should be nearly right away,
inside a minute it's fine.  If this isn't happening, you have a leak somewhere or some other related problem.  The system is self bleeding
essentially, until it's sucking in air somewhere.  Also, that seeming to pull fuel into injectors you are seeing with the clear lines is quite likely an optical illusion,
it's not possible for the injectors to suck fuel back in.  There is also very, very little flow/pressure in those overflow lines, it's why that little rubber cap on the end
one is sufficient.  They are there to provide a path back to the tank for any fuel that leaks around the nozzle inside the injector body, fresher the injector, the less fuel in those lines ime. 
Put a long hose on one and run it and see how much fuel comes out, it's generally not a lot.  Fuel or air in those overflow lines
should have zero impact on how the thing runs, other than making a mess they will run just fine with no hoses on them at all.
Beyond getting the IP full of fuel, and doing a gross bleed of the injector hardlines, that's it.  The system bleeds itself while running.


You might start with soaking the whole area in brake cleaner to remove any fuel, blow or let it dry off, then run it and look for weeping.
You can also put a long rod or screwdriver or mechanics stethoscope on each injector and pretty clearly hear when they pop at idle, if there is
air which compresses, they will not pop, fuel does not compress and makes them pop(which is to say, open or spray).

When was the last time that pump was re-sealed or the injectors rebuilt?
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Reply #8December 09, 2015, 05:24:21 pm

Sauerkraut

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Re: bleeding air out of fuel lines on AAZ
« Reply #8 on: December 09, 2015, 05:24:21 pm »
there was an audible difference when I cracked each hardline open, I could also hear what I believe to be "nailing" while doing so. I've owned the vehicle for just over a month now and to my knowledge, the injection pump has not been re-sealed, nor have the injectors been rebuilt.

there seems to be a little more clatter than my old TDi, but I'm uncertain if this is normal. a local VW shop suspected that my injectors were on the fritz and may need to be rebuilt. they've also adjusted the injection pump but noticed no performance difference.

normally, it runs fine and does not show air in the return line until it randomly and intermittently acts up. when it does, there is a constantly flow of bubbles in the return line until I let it idle for a while. I've replaced the clamps and sealed everything as best I can with new hosing recently and have only driven a few KM after doing so, someone mentioned that I should drive it for a while to let it "work itself out" before digging deeper into the vehicle.

Reply #9December 09, 2015, 06:14:15 pm

wolf_walker

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Re: bleeding air out of fuel lines on AAZ
« Reply #9 on: December 09, 2015, 06:14:15 pm »
If it's not nailing like crazy it couldn't hurt to drive it a bit, but in my experience thing settle down pretty quick with air and such if the system is tight and in good shape.
I think I'd get someone reputable to rebuild the injectors since they are an unknown, and are cheaper than getting into the pump.
Those also might be dual stage injectors, I think the AAZ or at least some of them had those, might just have to buy a set of new/rebuilt, I'm told
they are not as easy to rebuild as regular ones.
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Reply #10December 09, 2015, 06:26:52 pm

Sauerkraut

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Re: bleeding air out of fuel lines on AAZ
« Reply #10 on: December 09, 2015, 06:26:52 pm »
that's what I hear, I found a great write-up on how to rebuild the (seemingly) single stage injectors, and I believed I could pull it off without a hitch, but the dual-stage is what has me perplexed. I also saw some nozzles on here from a vendor/member named SMOG or SMOK I believe, he lives here in Canada, so I debated getting those and having my rebuilt with the new tips.

who do you recommend to have the work done? I was quoted $400cdn to have them rebuilt with new nozzles from GILES.

Reply #11December 09, 2015, 09:27:46 pm

wolf_walker

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Re: bleeding air out of fuel lines on AAZ
« Reply #11 on: December 09, 2015, 09:27:46 pm »
Giles if you can afford it lol..   Otherwise I dunno in Canada, there are a bunch of pump shops in the US, hit Yelp or whatever lists businesses there, or call up a local diesel repair place
and ask who does theirs maybe.  I think, but can't swear, that if you take the delivery valves to match with them you can use single stage injectors, but that might be introducing
more variables into a problem already.
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Reply #12December 11, 2015, 01:02:53 pm

vanbcguy

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Re: bleeding air out of fuel lines on AAZ
« Reply #12 on: December 11, 2015, 01:02:53 pm »
Single stage injectors aren't the same size as dual stage so the injector hard lines don't fit if you try and use older single stage injectors. You can try bending the lines to fit but they may crack if you do that and they are fairly rare and expensive on their own.

There are very few places that can do 2 stage IDI injectors. They are not very common to begin with (I don't think anything but the AAZ used them in North America and that was Canada only). Giles can do them though.

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