What's this fitting coming from my LDA and why is it blocked

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timmayjimmay
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What's this fitting coming from my LDA and why is it blocked

Post by timmayjimmay »

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I started messing with the max fuel screw on the back of the pump in an attempt to get more power and now there is fuel dripping from the LDA vacuum port. I popped the cover off and found the LDA full of fuel and it was slowly percolating past the rubber diaphragm. There are two fittings on the back of the spaceship, bottom is fuel return and top is blocked off (by previous owner). Where does the top one go? If it were actually connected somewhere it would let the LDA drain. Man, I should've just left that max fuel screw alone. Now I get smoke all the time and it stumbles when in low RPM conditions. Dang these pumps are finicky.
Last edited by timmayjimmay on Wed May 20, 2009 10:59 am, edited 1 time in total.
Vincent Waldon
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Post by Vincent Waldon »

Bottom fitting (the one your arrow is pointing to) is the fuel return for the pump and should have a bolt labeled "OUT" on it... the bolt has a small precise orifice drilled in it that's essential for the pump's internal operation, in particular, dynamic advance.

The fitting at the top of the LDA is a banjo connection to the intake manifold... it's how the LDA detects boost and adjusts the fuel profile accordingly.
Vince

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timmayjimmay
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Post by timmayjimmay »

Nope! The connection to the manifold is actually a small barb fitting/banjo on the top cover, this banjo fitting is on the spaceship body directly above fuel return line. The banjo comes from the bottom side of diaphragm and appears to be a drain for the fuel that has accumulated in the spaceship. This is supposedly stock 1983 Quantum stuff. The previous owner stuffed a screw in the line coming from it. Actually, it appears the pump was rebuilt by "ND" as they safety wired everything (including the screw in the hose!) and tagged the safety wire with tamper proof plastic logo dots. I am driving the car around right now and doing all this posting on my laptop as I go so the situation could develop as the day goes on.
libbybapa
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Post by libbybapa »

The fitting that is labeled "Unknown" is the atmospheric bleed. It should be open to atmosphere. It usually just has a little rubber boot on it that has a hole in the end of it. The topmost fitting is the boost line from the intake manifold. As boost pressure builds on one side of the diaphragm, with the other side of the diaphragm open to atmosphere, the pin moves downward delivering additional fuel to to accompany the additional boost air. There should not be any fuel inside the aneroid assembly. It will ruin the diaphragm. There is a small "feeler pin" that rides against the large tapered boost pin. Around that feeler pin is an o-ring that prevents the fuel from inside the pump from entering the aneroid assembly. Yours has obviously failed. To swap that o-ring is the following procedure:

Remove the aneroid top and diaphragm/boost pin.

Mark the relationship between the accelerator lever and it's central shaft. Remove the accelerator lever and springs.

Remove the four allen head screws that hold on the pump top and remove it.

When flipped upside down, you will see the aneroid lever that acts on the control collar lever assembly. It is held in by a rod that is in turn held in by a flat head screw on either side of the assembly. Remove the screw, remove the rod using a drift and remove the lever.

Remove the feeler pin using needle nose piers.

Remove the allen head plug opposite the atmospheric bleed.

Using an appropriately sized allen head bit, remove the o-ring keeper.

Remove the o-ring.

Assembly is the reverse. :-)

Andrew
Vincent Waldon
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Post by Vincent Waldon »

Ah yes... second picture makes it clearer for sure. :wink:
Vince

Edmonton, Alberta, Canada
2001 silver TDI Jetta Malone Stage 1.5 , 2001 blue TDI Jetta SBIII 216s Malone Stage 3
1970 Bay Window bus

Gone but not forgotten: 1969/1971 Beetles, 1969/1974 Westies, 1979 Rabbit, 1986 TD Jetta, 1992 gas Jetta, 1994 TD Jetta

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timmayjimmay
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Post by timmayjimmay »

Yeah I changed the pic so you could see it better. So if the seal went bad a good mechanic simply sticks a nail in ther leaky vent hose, I see... looks like I get to take the pump apart today. Thank you Andrew for the breakdown. This might also explain the gratuitous lack of power I have been experiencing. Incidentally, and to confuse everybody here, my name is also Andrew.
libbybapa
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Post by libbybapa »

Without the atmospheric bleed, your boost enrichment will not work. Definitely lack some umph without it, especially if it's filled with fluid or even pressurized by pump internal pressure if the leak is bad enough. :shock:

You will need the appropriately sized diesel rated o-ring. I know it is part of the Bosch DGK121 seal kit. Irritatingly, I've "kept" the part number for the specific o-ring over on the GTD forum which is currently down...

Also, that fitting should not be a banjo. It should just be an odd cap to the port with the aforementioned rubber boot thingy. Kinda makes me wonder if it's an altitude compensation pump that someone swapped in. Take some pics of the internals of the aneroid while you have it apart and post them up if you can.

Andrew
timmayjimmay
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Post by timmayjimmay »

Hello LDA! You are my new best friend! I uncorked that plugged atmospheric vent and BOY does she scoot when that turbo boosts. No smoke either. It is still dripping fuel so I stuck a can under it with a large magnet until I get a seal kit.
timmayjimmay
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Post by timmayjimmay »

libbybapa wrote:Without the atmospheric bleed, your boost enrichment will not work. Definitely lack some umph without it, especially if it's filled with fluid or even pressurized by pump internal pressure if the leak is bad enough. :shock:

You will need the appropriately sized diesel rated o-ring. I know it is part of the Bosch DGK121 seal kit. Irritatingly, I've "kept" the part number for the specific o-ring over on the GTD forum which is currently down...

Also, that fitting should not be a banjo. It should just be an odd cap to the port with the aforementioned rubber boot thingy. Kinda makes me wonder if it's an altitude compensation pump that someone swapped in. Take some pics of the internals of the aneroid while you have it apart and post them up if you can.

Andrew
I will take it apart right now. There is a star ring under the diaphragm so I am assuming. Its an lda.
timmayjimmay
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Post by timmayjimmay »

More pictures. This is the interior of the spaceship. What's the difference between the LDA/ADA? I did a search but didn't find any good pictures on the forums with a comparison. Someone send me a picture of an ADA and I'll do a nice side-by-side. This device of mine definitely adds fuel as boost increases so it must be an LDA. It is working wonderfully now and has miraculously stopped leaking fuel now that it is unplugged. I do not understand why the previous owner plugged it. I'm havin' fun now with my Q. I'm off to the local FBO to purchase some 120w Aeroshell for the crankcase per Hagar's experiences.

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surfcam
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Post by surfcam »

I think LDA has boost enrichment and feeds from the manifold from the top of the diaphragm. The ADA feed from the bottom of the diaphragm to some kind of a container? It only has atmospheric enrichment (elevation).
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Josh
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Post by Josh »

I saw one quantum that had the non-functional cruise control removed; I think they had plugged this atmospheric vent with caulk and a screw, thinking it was an associated vacuum mechanism. Could be that yours was plugged just because somebody didn't know any better. It'll be interesting to see if your over 60mph towing problem disappears now!
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timmayjimmay
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Post by timmayjimmay »

Well, although it seems that there's more power, the towing thing isn't too great. I'm getting an S10 to pull the trailer but it was a worthy effort on the VW's part. After all the jacking with the fuel screw it is now PROFUSELY leaking. It appears to be leaking out of the threads past the lock nut. It's late and I have to wait till tomorrow for the parts store to open so I can stick some teflon on it.
libbybapa
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Post by libbybapa »

There's an o-ring around the max fuel screw. It sounds like it might be worth doing a full pump reseal.

There are quite a few things that can be done to increase performance fairly dramatically. I'd recommend going over to the GTD Forum (back up and running now :D ) www.vwdiesel.net and reading up in the IDI Engine section and the FAQ section. You should be able to add 50% more HP fairly easily without any significant sacrifice in reliability.

Andrew
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Post by Diesel Dean »

My atmospheric bleed is weeping fuel. What do I do to make it stop? It make the injector retuen line wet with fuel drips right on the line. I do have some seals from a N/A pump seal kit.
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