[nickyt]

touakrid, these two threads might help explain the 30 second problem.

Quick easy questions on bad fuel pump symptoms.

Read through dozens of pages on the fuel pump issues. Couldn't elicit straight answers from any of the posts. Was hoping for some clarification. My Touareg sputters and dies after 30 seconds. After the priming pump turns off. Leading me to assume the main pump is dead. On an 04 v8, passenger...

www.clubtouareg.com

fuel pumps

I need help with yet another fuel pump problem. My primary pump failed and I replaced it. The car started and ran fine a few times over a few days and then wouldn't start again. Instead of starting up instantly it cranked for two or three seconds so I suspected that the secondary pump was no...

www.clubtouareg.com

 

[TRespect]

The only question I had pondered was about the flange used for the Phaeton. The Phaeton used a external fuel filter so it is possible that a Phaeton flange would be plumbed correctly.

Now if you want to talk about sourcing an unicorn part, that would be it. Wonder how many of those flanges are in North America, including in recycle yards. Less than 50 is my guess.

What might be slightly more useful is the list of fuel filters that fit the Phaeton.

Mann WK7301
Hengst H111WK
Mahle KL79
Beck/Arnley 0431025
Hastings GF318
Wix 33521
VW 1J0201511A

The phaeton has the filter outside the tank and uses a return line. The filter is a filter only. You can have the same setup on the treg but you need a return line. I don’t even see a regulator on the phaeton fuel system. They have a pressure valve or something which might be doing the sane job but I’m not sure. I’ll post the phaeton diagram later.


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[TRespect]

Next problem...

I tested the fuel line at the exit from the tank (RHS) after putting everything back together, and it holds the pressure really well ( 10min). I also measured the output of both pumps at the tank flange and it is fine (800ml in < 10s). So the filter can't be clogged, and there are no other obstructions.

But, the car stalled after about 30s of running, then started and ran fine.

The only thing I noticed is that the left side pump only has about 3 bar pressure, while the right has the required 4 bar.

I am worried it has something to do with the fuel levels and the decision by the ECU which pump to run and when.

What could this be now?

Could it be the problem happens as soon as the higher pressure (RHS) pump stops, and as it switches to the LHS pump which has lower pressure, that sudden drop from 4 to 3 bar causes the random stalling?

You need to get some fuel hose quick release connectors and test the pumps pressure at the pump hose. Get a 10mm and an 8mm male connectors. Disconnect the pumps from the filter. connect the connectors on gauge using another fuel hose and plug the pump to the gauge then turn it on with relay. Be very careful and take all precaution to avoid hurting yourself with the pressure or starting fire. You can test the pumps outside but you will need a lot power supply with a lot of amps. I’ll have to look up the spec of the pumps to see what voltage and amperage is required. I think testing the pumps inside the tank is a good option as long as you are very careful. Remove both relays and plug the unused pump hose closed before putting the relay. Keep the pump powered on the gauge for 10/20mn to see. Do you get the idea?
This test will bypass the filter and the regulator. You might be seeing up to 6bar pressure. BUT be very careful.


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[touakrid]

Too much effort and totally unnecessary. The filter by its nature has no effect on the pressure, neither do the valves or the hoses. They impact throughput only.

I know that my left pump has low pressure, so maybe the inlet mesh is clogged or it has worn carbon brushes or the impellor is loose. I will take it apart and look at it, I have fixed electric motors before.

What no one seems to know is how the ECU agorithm really works that controls running the pumps alternately. I think it has to do with the fill levels of the tank halves and maybe the O2 sensors, because there seems to be no pressure or flow sensors for the fuel. Maybe there is a time factor or it takes other parameters into account. I can find out when I next open the tank if pressing down the fuel level floats triggers the one or the other pump.

 

[TRespect]

I read somewhere it has to do with fuel fill level. When under 1/5 of fuel fill both pumps kick in. You might try that to see how the engine starts and drives when under 1/5 compared to more than 1/5 fill.


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[TRespect]

Next problem...

But, the car stalled after about 30s of running, then started and ran fine.

What could this be now?

Could it be the problem happens as soon as the higher pressure (RHS) pump stops, and as it switches to the LHS pump which has lower pressure, that sudden drop from 4 to 3 bar causes the random stalling?

Did it stall only once after you put back everything together or does it stall every time you start it? The drop in pressure might explain the stall. I don’t know how the system monitors the pressure. There are no sensors there. You might have a bad fuel injector which once activated (engine on) starts leaking or sticks open. Just a wild guess. I don’t know if a leaking injector can trigger a misfire code.


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[touakrid]

Interesting, I wonder would that be 20% full in litres total, or in fuel level height, or perhaps impedance as measured by the fuel level sensors? How does it apply to left and right fill levels? How does the petrol get from the left half of the tank to the right, where it has to be so it can be sucked in by the supply pump?

 

[TRespect]

VW magic
You will have to go in there to find out. Each side should have its fill level monitoring I guess.


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[touakrid]

Did it stall only once after you put back everything together or does it stall every time you start it? The drop in pressure might explain the stall. I don’t know how the system monitors the pressure. There are no sensors there. You might have a bad fuel injector which once activated (engine on) starts leaking or sticks open. Just a wild guess. I don’t know if a leaking injector can trigger a misfire code.


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Only once, then it started fine and ran for a while but stalled twice again on the way to the petrol station. Definitely lasted longer than 30s, but stalled upon accelerating at lights (that's especially funny in the rush hour traffic 🤣).
I don't know about leaking injectors, but then I should have codes, or high consumption, or rough running, misfires or smoke, or funny noises. Do you agree?
I will listen for the 6 injectors to all be clicking tomorrow morning.
Good suggestion though, maybe I have a combination of problems.

 

[touakrid]

VW magic
You will have to go in there to find out. Each side should have its fill level monitoring I guess.


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But how does the petrol from the left half get to the right half? This could only happen when the pressure regulator opens, which would mean pressure of more than 4 bar. Hmmm...

 

[TRespect]

I was going to suggest listening to the injectors with a metal piece but they are under the intake manifold. Try it though. You do not have any sensor fault codes. Mine stalked on me a few days after I bought it after leaving a traffic light and vcds reported a speed sensor intermittent error. I replaced the speed sensor and it never did it again.


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[touakrid]

touakrid, these two threads might help explain the 30 second problem.

Quick easy questions on bad fuel pump symptoms.

Read through dozens of pages on the fuel pump issues. Couldn't elicit straight answers from any of the posts. Was hoping for some clarification. My Touareg sputters and dies after 30 seconds. After the priming pump turns off. Leading me to assume the main pump is dead. On an 04 v8, passenger...

www.clubtouareg.com

fuel pumps

I need help with yet another fuel pump problem. My primary pump failed and I replaced it. The car started and ran fine a few times over a few days and then wouldn't start again. Instead of starting up instantly it cranked for two or three seconds so I suspected that the secondary pump was no...

www.clubtouareg.com

Thanks for that. Everyone seems to have different issues, but mostly it didn't get solved by the VW mechanics, but made worse

 

[touakrid]

I was going to suggest listening to the injectors with a metal piece but they are under the intake manifold. Try it though. You do not have any sensor fault codes. Mine stalked on me a few days after I bought it after leaving a traffic light and vcds reported a speed sensor intermittent error. I replaced the speed sensor and it never did it again.


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What speed sensor? I will check with vcds again tomorrow, maybe it has some interesting stuff in there, like misfire counts or lean/rich condition

 

[TRespect]

But how does the petrol from the left half get to the right half? This could only happen when the pressure regulator opens, which would mean pressure of more than 4 bar. Hmmm...

Petrol does not get from one side to the other. Both pumps run when fill level is less than 1/5. The passenger side pump works on it’s own until the level is at the wall level separating the tank sides. Then both pump work together. I also read somewhere that both pump are used when under load. But this is all guess work. Needs confirmation.


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[TRespect]

What speed sensor? I will check with vcds again tomorrow, maybe it has some interesting stuff in there, like misfire counts or lean/rich condition

Yes. Do a vcds scan. The speed sensor is also called g28 sensor or crank sensor. If this guy starts acting you will have the treg either not starting or stalling randomly. It started fine on mine but stalled many times in traffic until I replaced the part. Vcds will report it though.


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[touakrid]

I did have the relays jumpered for a while, so that both pumps were always running if at least one was triggered by the ECU. That actually worked and I didn't have any issues. I removed this bridge though when I fixed the filter seal leak and prompt it started stalling.

 

[touakrid]

Yes. Do a vcds scan. The speed sensor is also called g28 sensor or crank sensor. If this guy starts acting you will have the treg either not starting or stalling randomly. It started fine on mine but stalled many times in traffic until I replaced the part. Vcds will report it though.


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Ok. Sounds like a plan.

 

[TRespect]

What about a bad relay. It was upgraded later by vw. Original was 404. Now it’s 464 I think. You can swap the relays to test.


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[touakrid]

What about a bad relay. It was upgraded later by vw. Original was 404. Now it’s 464 I think. You can swap the relays to test.


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Relays are so simple. Of course I tested them all and they look pristine. You think one may randomly switch off and on? Or a mechanical fault in a relay/switch or connector? I will look at this and ensure it is not the case. The engine stalled a few times randomly but only under load and while the fuel is very low.

Now that the tank is full the car drives fine again, so I have my money on the weak pump, which I will diagnose further this weekend.

 

[touakrid]

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?