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TDI Conversions Discussions on converting non TDIs into TDIS. More general items can be answered better in other sections. This is ideal for issues that don't have an overlap and are very special to swaping engines.

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Old February 15th, 2019, 16:13   #1
johnfm3
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Default MK4 Fuel Tank Gas vs TDi

I am looking for information on the differences between the Gas and TDi fuel tanks.


There is the obvious issue with the flap in the filler neck.


Can anyone tell me if the TDi fuel pump assembly will fit a Gas (non tdi) fuel tank?


I am performing a TDi swap in a 99 Mk4 jetta with a 2.0 and a 5sp and I have a donor car which is a 2001 Mk4 jetta TDi with a 5 sp. So I can pull the fuel tank if needed, but it looks not so fun and if I dont have too, I would rather not. More so, I am abit nervous trying to get the car high enough in the air to make pulling the tank easier while in my garage.


I have pulled the old exhaust so thats out of the way if I do need to pull the tank.



Thanks,
John
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Old February 15th, 2019, 16:14   #2
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And now back to the garage to work on other items.... Thanks again
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Old February 16th, 2019, 05:10   #3
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Pick your rear passenger seat up to access the sender unit and see if you can switch them out to the existing lines. If that is an alh you don't have a pump in the tank unless someone installed it.
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Old February 16th, 2019, 06:59   #4
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Quote:
Originally Posted by jmodge View Post
... If that is an alh you don't have a pump in the tank unless someone installed it.

Thank you. I just assumed that the both had a in-tank pump.


So 2001 being a ALH TDi, does it have a electric pump under the chassis, or only the main pump at the engine?
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Old February 16th, 2019, 07:06   #5
johnfm3
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Ok, follow up to the prior question. If there is no electric fuel pump in a ALH TDi, what does the Relay 109 do for the fuel system?
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Old February 16th, 2019, 07:38   #6
Vince Waldon
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The ALH has no lift pump- the injection pump does it all.

The injection pump is controlled by the ECU, which is powered by Relay 109.

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Old February 16th, 2019, 07:51   #7
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Quote:
Originally Posted by Vince Waldon View Post
The ALH has no lift pump- the injection pump does it all.

The injection pump is controlled by the ECU, which is powered by Relay 109.

Sent from my Nexus 7 using Tapatalk

Ok, thats news to me. This clears up much confusion as to the different options I am reading about.


Also re lights the fire to continue on this project. I was looking at the project ahead of me and was about to scrap my Mk4 Jetta and give up.


Thanks,
John
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Old February 16th, 2019, 08:29   #8
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Ask yourself how comfortable you are with wiring, I think that is where the major part of this project lies
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Old February 16th, 2019, 09:46   #9
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Quote:
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Ask yourself how comfortable you are with wiring, I think that is where the major part of this project lies

I am normally not worried about wiring. And with a complete donor car, thats not what really bothers me. I am hoping to minimize what gets moved over, and utilize as much of the existing parts as possible. To reduce the amount of possible damage as a result of pulling a 20yr old car apart.


My car is in such great shape, I would be out $10K to replace it in a TDi due to body condition alone. Full leather (Black and Tan interior), sun roof, limo tinted windows (5%), 17in wheels with summer tires, projector headlights and LED tail lights, and a nice sound system. And I want to try to keep it that way. I could not afford to replace what I have for a TDi version, which is why the project to swap it.
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Old February 17th, 2019, 16:34   #10
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New question related to the fuel tank.


So I was able to confirm that the whole fuel level sending unit fits in the 2.0L gas fuel tank. It looks like there are some added vent lines (2 white lines) which go to the top of the fuel tank, can those remain open during the initial testing of the TDi? Does the TDi fuel tank get pressurized?


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Old February 18th, 2019, 08:31   #11
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Tank is not pressurized, alh pump only needs supply suction and return lines, there is only the two on your TDI, correct? I saw a thread in just recent weeks on this swap.
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Old February 18th, 2019, 08:35   #12
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Quote:
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Tank is not pressurized, alh pump only needs supply suction and return lines, there is only the two on your TDI, correct? I saw a thread in just recent weeks on this swap.

The donor car (2001 Jetta TDi) only has 2 lines, 1 Black and 1 Blue line.


The target car (1999.5 Jetta 2.0L) has 4 lines. 1 Black, 1 Blue, and 2 whites.


At this time I am ignoring the white lines. The question to the community is do I need to cap them off? When I can make the tank swap (after car is running), I will remove the 2 white hoses completely.
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Old February 18th, 2019, 10:04   #13
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It is easy to get the tanks out. You do need to drop the rear beam, but that is pretty easy. Takes 20 minutes. Then the tank is right out in the open.

The gas cars have all the evap stuff with them, and depending on model/engine, can have totally different plumbing with the lines, and their filter is on the side of the tank.

Seriously, if I had both cars, I would just get the tank swapped over. It won't be nearly as much work as the rest of the swap.

And the car almost certainly needs parking brake cables anyway, plus you'll want to upgrade those to the later type and later rear calipers anyway.

So to that end, I's swap the whole rear beam in too.
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Old February 18th, 2019, 16:11   #14
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Just need to watch the brake lines which will twist the line up if you are not careful. The nut rusts to the line and makes the job a nightmare. Heat is the only way to prevent it...
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Old February 19th, 2019, 03:13   #15
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Yes, those poor folks in the rust belt would have to deal with that I'm sure. Around here, and I suspect where the OP is from, VAG products' brake lines are never an issue... now ChryCo and GM stuff on the other hand....
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