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Discussion Starter · #143 ·
Hi. Does anyone know why the pumps have a suction jet attached to them? That's the extender arm that is clipped into the pump housing and reaches towards the front of the tank. While the pump sucks fuel from its floor through the mesh there, according to the diagram the suction jets cross over between the two sides. I wonder where the fuel really flows. I also wonder if the regular shouldn't always send some fuel back into the tank, which would require the pump pressure to be higher than the calibration of 4 bar?
Has anyone run this system outside the tank and can comment on these aspects?
We need a tank teardown :)


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Discussion Starter · #144 ·
Getting bac to this soon.
Main pump is suffering when fuel fill level is above 1/5. When the refuel message appears the secondary (startup pump) kicks in and the suffering ends there :)
The main pump is probably suffering due to the 18 years old clogged fuel filter. It might also be on its way out.
I will be doing the Mann filter mod soon bypassing the oem filter. I will test with both a filter only and then with a filter with integrated regulator. If the filter does not fix it I will test the pumps. If the secondary pump is still good and the main one is dying I plan to swap them, putting the secondary one in place of the main one housing and vice versa.
Will update when I get the job done.
Filter purchased:
Mann WK 512 (filter only).
Bosch F026403006 (filter with integrated 4bar regulator). Mann part is WK 69/2. 4bar.
I bought a submersible fuel hose and some quick disconnect fuel connecters to test before modding the oem hoses. I would like to still be able to go oem if needed.
In the case of the filter with integrated regulator I will be using two regulators but this does not disturb the desired flow as the filter regulator will be letting out 4bar and the oem one will not have to bother since it will always be seeing 4 bar or pressure. Pics and drawings soon.
 

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Discussion Starter · #145 · (Edited)
So I did manage to open the 18 years old untouched fuel system.
Left side plug is a pain (Behind the driver seat => LHD). I even had to break the tab at the third or fourth time I had to disconnect it. Now it's easier to remove.
I made a Y connection to connect both pumps and bypass the original fuel filter housing but one connector didn't fit. It was a tad too big for the left left pump connector (behind driver's seat). I then opened the fuel filter and removed the filter. It was clogged. I screwed the filter housing back without the fuel filter. Took some fiddling to make sure not to pinch the o-ring. I Connected both pumps and went to the right side (behind passenger seat = LHD). I created an extension so as I can put the Mann filter (WK512). I used an angle quick disconnect 8mm connector and a straight quick disconnect connecter. I used a submersible rubber hose. I put a ground wire on the Mann filter housing and connected it to the ground wire on the regulator. I tightened the wire with a zip tie around the filter. I will have to go back there and check that the zip tie has not dissolved in fuel :) I added another zip tie to prevent the filter from moving around. I attached it to the regulator.
Car is running fine. Pressure is around 3/3.30 bar with both pumps on (less than 1/4 fuel fill). BUT the pressure is still not there with the right side pump (main pump when cruising). I will have to switch pumps or replace that one. I have a used spare one I'm going to test first.
As for the fuel filter mod I think I will be going for a complete relocation of the fuel filter and regulator. Getting access to the pumps is a pain. I don't want to go back there and unscrew all those m10 screws and fight with the hoses just to be able to replace a regulator or a filter. SO I'm planning on pulling a heavy duty fuel hose to the engine bay or to the bottom of the Treg and connecting a filter with an integrated regulator there.
Pics coming...
 

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Discussion Starter · #147 ·
So I finally managed to completely bypass the filter and use my modded Y pieces to connect both pumps to the Mann filter. I get 3.5 bar or pressure with both pumps but above the refuel level the Treg starts to cough and struggle. I wen ahead and replaced the right pump with the used one I got from ebay (came from porsche) just to test and the result was worse. with bothe pumps running I get 2.5 bar or pressure. Treg is running fine and acceleration is good. This means you can run with either one pump or two pumps if the pressure output is at least 2.5 bar. I tested the used pump alone and it outputs 1.0/1.2 bar of pressure. So yes the kit I got for learning purposes was a scam. Ebay seller was listing it as fully functional but I was not expecting it to be like new. I learnt what I wanted from it and was able to make my filter kit. Pics coming. I will order a new VDO pump.
 

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Discussion Starter · #148 · (Edited)
So there are two pump part numbers for the T1/T2 gasoline engines:
1: MPI engines: 2002-2006 > 4 Bar pressure => Dual pump setup
Right pump VW 7L6 919 087 G VDO 228-236-005-016Z
Original VDO Continental pump page
Left pump VW 7L6 919 087 F VDO 228-236-005-017Z
Original VDO Continental pump page


2. FSI Engines: 2007-2010 > 6 Bar pressure => Single pump setup + High Pressure Fuel Pump (HPFP) in the engine bay.
Right pump VW 7L8919087B VDO A2C53377801Z
Original VDO Continental pump page


Both engine types have different fuel filters and fuel regulators. The MPI engine (pre-FSI) have 4 bar pumps, a simple fuel filter with no check valve whereas the FSI engines have a single 6 bar pump with a different fuel filter and 6 bar regulator.

So be careful when shopping for these guys as websites list 6 bar pressure pumps compatible with all T1/T2 models. The 6 bar pumps will work in the MPI engines but the fuel regulator (4 bar) will constantly be dumping around 2 bar of excess pressure back into the fuel tank.
If you buy a complete 6 bar setup (pumps + filter + regulator) for an MPI engine like a 3.2 or 4.2 or 6.0 engine you will be using 6 bar of pressure in a system which was designed for 4 bar of pressure. It will work as the hoses are designed to tolerate more than advertised pressure but you will be stressing the system. Even the 6L W12 uses a 4 bar pump setup. The W12 is an MPI engine in both T1 and T2 generations. I don't know how the oem injectors will handle the 6 bar pressure in the case of a full 6 bar setup in place of a full 4 bar setup for an MPI engine.

Regulator for MPI: 7L0919679A
Regulator for FSI: 7L6919679E

Fuel filter for MPI: 7L0919679
Fuel filter for FSI: 7L6919679D

And of course these is even more to the pump part number mess. There are pumps designed to work with Ethanol fuel so you have to be careful if you have an Ethanol setup

Right pump for an MPI Ethanol setup: 7L0919087H
Left pump for an MPI Ethanol setup: 7L0919087G

Right pump for an FSI Ethanol setup: 7L8919087C

Left is behind the driver side (LHD drive cars) (secondary pump)
Right is behind the passenger side (LHD drive cars) (main pump)

By the way my treg does start with either one of the pumps connected. But it does switch to the right pump after a few seconds. The left pump is activated under load (when you floor it) or when the refuel message appears on the dash.
The first hesitation I had was when I tried to pass a car on the freeway and the treg like went into neutral for a few seconds. I had just done a transmission flush using the transmission cooler lines and replaced all the old fluid. I suspected the tranny was acting up after the flush. I had this happen on two or three occasions and started to anticipate and put the treg under load before passing vehicles. One day it went shaking and misfiring after a refuel at the gas station. I started looking at the pumps and noticed that, like the lean condition, this shaking and loss of power was also cured by running the Treg with the refuel warning on all the time. This means doing gas stops more often. I then tested the pumps and came to the conclusion that it was time to get a new right pump. The left one being less solicited is the one making the Treg still run for the moment.

And like always please double-check or call the dealer and give them your vin number before buying these parts.
 

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Discussion Starter · #151 · (Edited)
The Y piece to connect both pumps. I initially thought the left pump quick disconnect connector was 9.89mm. It is 9.49mm. So I had to replace it (on the pump hose) with a 7.89 like the right pump one. I used a hot air gun to warm up the hose on the connector and removed it then warmed it up a little bit to put the connector. I did this with the pump out of the tank of course. I didn't want the heat gun to get in contact with the fuel vapors.
Y piece before: (notice the size of the connectors)
Toy Cosmetics Finger Tints and shades Nail


Y piece with 7.89 connectors on both inlets:

Product Automotive tire Tread Sleeve Camera lens


Sleeve Automotive tire Finger Nail Tool


I used a submersible fuel hose because I didn't want to touch the oem hose in case I needed to go back to the oem setup. I have a used set of pumps but I hadn't tested them in the car so I wasn't going to take any risks there.

And the Mann filter WK512 installed inline on the right pump side (attached to the regulator with a zip tie (pic was taken before strapping the filter to the regulator) to prevent it from moving around). The filter comes before the regulator of course. This filter is a simple filter with no integrated regulator. I also grounded the filter body just to avoid any electrostatic discharge.
I made sure any protruding metal piece is not touching the tank walls or the any other hoses.

Hand Motor vehicle Automotive tire Gas Hood
 

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Discussion Starter · #152 ·
And on the filter side there is the Y piece resting near the pump.

Tire Wheel Land vehicle Bicycle wheel Bicycle tire


Now that the filter has been tested for a over a week I will be relocating it to the filter side. I will remove the lower part of the filter (screwed part) and make a fitting spot for the Mann filter so that it does not start dancing in the tank when driving.
 

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Discussion Starter · #154 ·
The final mod will be:

Modding the fuel regulator flange to add a quick disconnect male port for the fuel return line.
Making a custom holder for the 4 bar Mann filter with integrated regulator under the Treg.
Cutting the fuel hose under the tank and connecting it to the Mann filter output (engine side)
Connecting the tank side to the inlet port of the Mann filter.
Adding a hose for the excess fuel (return line) to the tank and connecting it to the custom port.
This will get rid of both the oem fuel filter and oem regualtor.
This will make changing the fuel filter and regulator in one shot a breeze.
This will give your fuel pumps a long lasting life if you replace the Mann filter at least every 30k or 40k km.
The Mann filter/regulator WK 69/2 or Bosch F3006 are around 15$.
And it is a pain to fight open the OEM pumps and breathe those fuel vapors and mess with the connectors.
You will do it once then forget it. Seals will have to be checked and replaced if needed because you won't be going back there for while.
The kit details will be posted when everything is ready and tested.
This applies to MPI gasoline engines only for the moment.
I only have MPI Tregs available for testing (2 VR6 and 1 W12).
MPI stands for MultiPort Injection. This is the pre-FSI engine type.
 

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Discussion Starter · #155 ·
Fuel consumption with a healthy 3.2 VR6 cruising at 100 kmph with 3.45 bar pressure = two pumps running, refuel message on dash. I do have the BFG K02 tires on so fuel consumption should even be lower with standard all-season tires.

Speedometer Odometer Car Tachometer Vehicle
 

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Discussion Starter · #156 · (Edited)
So I did install a new VDO (right side) fuel pump. around 200€ shipped from germany.
I switched the Mann fuel filter to the left side. I removed the lower part (screwed part ) of the OEM fuel filter so I can get more space for the Mann filter. Treg is working fine BUT I still have that hesitation when flooring it if running with a fuel fill level above the refuel warning message. Looks like when running with the new pump only (above 1/4 fuel fill level) and hitting the gas pedal hard this ends up with a leak on the left side pump which when activated does fight back the pressure generated with the new pump and then the treg takes off. There is also the fact that now I'm using a Y piece instead of the OEM fuel filter. In the OEM filter setup both pumps are hitting the fuel filter before going out the regulator. This might take some of the pressure generated by the pumps down a bit. I will probably have the same behavior if I install a new left pump. I think I need some sort of baffle instead of the Y piece or a non return valve on either the left pump or the on both pumps to give them some extra life. I think the pump check valve is one of the weakest component and is responsible for the pump's short life. But considering the OEM pumps lasted 18 years that's already a loooong way.
I have some aliexpress non return fuel valves sitting in a drawer I will open one up to see what's inside and decide whether to give it a shot or buy a quality valve. The idea is to put the valve tight before the Y connection on the left pump side before the filter of course.

The non return valve:

Cylinder Engineering Auto part Font Metal
 

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I'm just flabbergasted at all of this. Why would VW engineers over-over-engineer something as simple as a fuel tank? It really shouldn't be this complicated.
 

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Discussion Starter · #159 ·
So I did the check valve test with the chinese part and it was a no go. The check valve internal blocage piece couldn't handle the pressure and was stuck half open.
Here is what I got from this experiment so far:
Treg does start even if the left pump is disconnected, I mean electrically disconnected.
My left pump does not supply enough pressure so I couldn't start the engine with right pump disconnected.
When Treg starts with both pumps connected the left pump is shut down after a few seconds.
Left pump failure is mainly due to two thing: tear and wear of the pumping system (propeller and motor) and failure of the non return check valve. In my case the pump is almost dead in terms of fuel pressure but what is causing the treg to fail to run above 1/4 fuel fill is the left pump check valve. When the left pump is shut off by the system the non return valve is there to close the line and prevent fuel from flowing back through the pump and causing a leak in the 4 bar pressure required by the engine. The Check valve is so worn out that with more than 1/4 fuel fill the Treg simply refuses to move. When engine is started the pressure goes up to around 4 bar, there is even excess fuel dumped back to the fuel tank through the regulator, then as soon as the left pump is shut down pressure goes down to around 2 bar and the treg starts shaking when I drive it. It does drive slowly around 30/40 kmph and sometimes it stalls completely. When the fuel level goes back to the red zone and the refuel warning message appears the ecu activates the left pump and this helps act as a barrier against the fuel pressure coming from the new pump and the Treg drives pretty good even accelerates like a rocket with the 220 HP VR6 :) 0 to 100 in less than 20 seconds :)

So here is my theory:
The left pump is shut off almost all the time, except when under load or when fuel level is less than 1/4 => More work and strain on the check valve.
The right pump is active all the time => less strain on the check valve.
This leaves us with the following conclusion:
The check valve of the left pump is closed and fighting against the pressure almost all the time.
The check valve of the right pump is in the open position almost all the time.
And this leaves me with three solutions:
Add a check valve (a good brand like the Pierburg one) on the left pump. I'm talking about adding this to my modded fuel lines and fuel fuel filter. It can be done on the OEM setup of course. You will need a submersible fuel filter and some ear clamps and quick disconnect connectors.
Put the right pump I removed in the housing of the left pump. This is supposing the right pump check valve is still strong enough.
Get a new pump. This I will do if my theory is rubbish and the two first solutions fail :)
A used pump will be dissected later to have a proper look at the internals.
Honestly I can't explain it otherwise. I can't find a leak in the system or the injectors. When both pumps are running the Treg is very happy. Not a single hesitation.
 

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Discussion Starter · #160 ·
Small but important update here:
I tested the pierburg valve and it worked for about 3 days. i insted it between the left pump and the bosch filter. I refilled half a tank and drove around for two or three days. Then the Treg started to stutter again. And when I apply the throttle it takes a few seconds to react since now I have two valves in series. So this confirmed my idea that the left pump valve was done and the leaking valve was the one causing the loss of pressure when tank is filled above 1/4.
Since I changed the right pump with a new one I had the old one still lying around. I removed the left pump, swapped the upper part on the used pump with the upper part of the left one since the hose is not the same as the right side and put the used pump in place of the dying one. And it's been working like new for more than a month now. The right pump valve is only used when the treg is shut down so it's not that worn even after 18 years of use.
Next will be the filter relocation outside the tank when I get the time...
 
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