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Discussion Starter #1
Hi guys, I have a question about my 2005 BMV engine, which takes long to start. Suspecting the fuel system, but fuel rail pressure is the required 4 bar, only when I switch off the engine it drops immediately to zero. VW manual says it shouldn't lose more than 1 bar over 10 minutes, well mine just snaps to zero. Interestingly, the engine starts much better if it hasn't been off for long, though after a few hours it takes 8-10 seconds to finally start.
Otherwise it runs fine, no misfires or any other engine issues, accelerates normal. No increased consumption, no fumes, no smells, no funny sounds. Ideas?
 

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Elsawin says pressure should be tested for both pumps separately. It also gives two separate causes for left and right pump.
Check my thread over here if you want to see what's going on inside your tank before throwing new expensive oem parts at the Treg :)
Fuel regulator might be dead. Can be replaced separately.
A leaking injector
or a dying pump. you have two on the Treg so test them separately.
They both go through the regulator so start there.
The last part of the video is pretty smart trick but in your case the regulator is in the tank so if the regulator is not holding pressure you need to replace it. Now get the tools and start digging :)


 

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Discussion Starter #3
That is awesome information, thanks so much. I hope it's not the injectors, but I guess the symptoms would be different if it was flooding the intake. I have some idea about the fuel pumps, filter and regulator flange etc, because I once took it all apart in order to find and replace the fuel filter, and fix the fuel gauge senders which had stopped sending. It's bloody complicated with the fuel circulating at 6 bar and being reduced to 4 by the regulator, though. I actually made a modification to the relays, so that both pumps are always running together. Couldn't see the point of supply and transfer, because both halves of the tank need to be emptied equally. However, with my latest issue, if the regulator was bad and was therefore not holding the pressure anymore, wouldn't I be setting the pump pressure of 6 bar at the rail, especially since the drop is so sudden when the engine stops? As you said, I will need to open the tank again and narrow it down to either one of the pumps, their backstop valves, regulator, or even something else... 😂 Happy days...
 

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You’re in for a fuel tank trip :)
Please take pics and document and do join my thread to see what I want to do to replace the filter and the regulator with an all in one easy to replace filter/regulator.

The regulator will only allow 4 bar I think. What happens if it is stuck? Need more digging into how this vdo regulator works.

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Have you checked your oil - both the level and the smell - just in case diesel is leaking down the bores into the sump?

The last thing you want is the engine going into an unstoppable max revs until the big bang event!
 

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Discussion Starter #6
TommyT, I will do some extensive diagnosis asap. However, the engine is a petrol one, and I did not notice any gas in the oil, but thanks for the tip. I believe that if the petrol pressure disappeared through an injector, it would flood the cylinder and upon starting up I would see quite a bit of smoke. I should also have a rich condition and fault code but I do not. Also no misfires being reported.
 

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Discussion Starter #7
You’re in for a fuel tank trip :)
Please take pics and document and do join my thread to see what I want to do to replace the filter and the regulator with an all in one easy to replace filter/regulator.

The regulator will only allow 4 bar I think. What happens if it is stuck? Need more digging into how this vdo regulator works.

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Will see what I can document. Also I need to see what the filter and pump strainers look like, at 325,000 km this will likely all need a good clean too.
 

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325 ! Waaou !
Get those pumps out and do some cleaning. Then pressure test the regulator before buying parts. People just replace everything when dealing with fuel issues on the Touareg. A total waste in my opinion. Check my fuel pump thread to see how some guys are opening the pumps and repairing them. I’m thinking about a fuel system mod I will add to my thread when I do it.


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Discussion Starter #10
325 ! Waaou !
Get those pumps out and do some cleaning. Then pressure test the regulator before buying parts. People just replace everything when dealing with fuel issues on the Touareg. A total waste in my opinion. Check my fuel pump thread to see how some guys are opening the pumps and repairing them. I’m thinking about a fuel system mod I will add to my thread when I do it.


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I will only get to it on the weekend. The fuel filter will deffo need to be renewed, but where to buy it? I am in Australia, lol. I might just wash it really well. Really interested to see if this pressure regulator actually is responsible for my rapid pressure loss after switching off, because I don't have any other issues than the long cranking time. This morning the engine took long (I had left the ignition on for a few seconds before cranking to prime the fuel line, but the effect was opposite to what I had hoped), then it started and idled only at 500rpm, then died as soon as I touched the accelerator. Second time was quick and perfect.
 

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Discussion Starter #11
I like your thinking, TRespect ;)
The VW dealers, or any other repairer here, would just blindly swap the entire fuel supply system and charge me thousands of dollars (no kidding). I am not prepated to invest much in a truck that old, it would be overkill.
 

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Plus you learn the physics of your horse ! Makes it easier to drive and more enjoyable :)
Check my thread if you want to learn more about the fuel system:




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So pressure is maintained by check valves, pumps and regulator in some way.
Looks like the priming pump which is used when you turn the key on and when you start the engine for 30 sec. This pump maintains the pressure for next startup. Check this video. 30 seconds after start the other pump takes over and you don't have any fuel issues.

 

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Discussion Starter #14
I have gone through your thread and watched all the Russian videos too. Good work! Especially the one guy who takes a huge hammer drill to the pump housing for whatever reason I can't fathom :)
As I mentioned, I made a mod to the relays for the pumps so that both pumps will always run when the ECU says one of them should. I don't get this VW idea of having a supply pump and a transfer pump, and run only the supply one constantly while driving, and the other only to keep the fuel level synced.
Therefore, when it primes the fuel system it uses both pumps (thanks to my relay mod), and they keep running together, which should not only wear them out more evenly but also shade the stress of maintaining the 6 bar pressure equally between the two.
 

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Good work! Especially the one guy who takes a huge hammer drill to the pump housing for whatever reason I can't fathom :)
That's a mystery to me too. I will tell why he did that when I get the used pumps.

As I mentioned, I made a mod to the relays for the pumps so that both pumps will always run when the ECU says one of them should. I don't get this VW idea of having a supply pump and a transfer pump, and run only the supply one constantly while driving, and the other only to keep the fuel level synced.
Therefore, when it primes the fuel system it uses both pumps (thanks to my relay mod), and they keep running together, which should not only wear them out more evenly but also shade the stress of maintaining the 6 bar pressure equally between the two.
I don't think that's a good idea because you will be putting too much stress on the regulator. You are pushing 2x4bar of pressure continuously. I guess the regulator and the fuel lines can handle the 8 bar up to the regulator but if the regulator breaks that pressure will be hitting the fuel lines and valves down the fuel system and the injectors and all that. I wouldn't do it that way. You better leave a pump in standby mode and enable it when the other one stops working while waiting for a new pump. You can buy the pumps separately now and replace like the Russian guy with the drill :) You can even get a Chinese one for 30$ and keep in the trunk if both pumps dies on you in the middle of nowhere :)
 

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Discussion Starter #16 (Edited)
237768

I tend to disagree. The pumps deliver 6 bar each, but by putting multiple pumps in the circuit it doesn't just add the pressures. In fact, the return line from the filter is pressureless. There is a pressure of 6 bar maintained in the circuit but the pumps actually don't strain against that all the time, they only need to build up the pressure lost through the regulator, and slowly suck fuel into the system via the Venturi pumps. If it was like you suggest, there would be different pressures between 0 and 12 bar on the regular at varying times, depending on the whims of the ECU to power the pumps
 

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On the VDO specs I see 4 bars for the Touareg pumps and 6 bars for the Cayenne. Might be a mistake and the pumps are the same, either 4 or 6 bar but that's not something I'd expect from a serious manufacture. I still need to verify the pressure on those pumps. The one I will be playing with come from Porsche so they will certainly be 6 bar. When I get my pressure gauge I will test mine too. Where did you get the 6 bar measure? Did you measure it on your Treg?
I don't see a return line from the filter. The return line is from the regulator with excess pressure. The ECU does certainly do it's magic not to have both pumps on all the time or at lease for a short period. When a pump in not used it maintains the pressure in the system with it's internal non return valves. I tend to try to replicate the system and make it bullet proof and not modify it without full knowledge of the consequences. I'm trying to put a filter and a regulator in the same device which just mimics the existing system with modern components which probably didn't exist at the time. But I wouldn't go against the engineers who did spend a bunch of years coming up with all the gymnastics. I don't say you're not right or it will not work but it might have other effects if not fully tested. I intend to put my setup to the test and I don't care if I lose 6 injectors and two pumps. I already have six injectors in the drawer and 2 pumps coming :)
Treg is not my daily drive. It's a toy I'm restoring so if it goes bang I'll just leave it in the garage till I fix it. If you depend on your Treg for your daily business you have to be careful about that.

This is for The 3.2 and some 4.2 engines:

237769
 

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Discussion Starter #18
Yeah, my Treg is a bit of a project, I don't use it daily. But to be safe, I will remove the wires from the relays and see how it runs then, and when I get time I will measure the pressures and feed back here. I have the repair manual for this engine, and it states 6 bars before the regulator, and 4 bars to the engine, well I get 3.9 bars at the Schrader valve on the rail once it runs. Except that it drops like a stone when I switch off.
By return line I meant the one running from the regulator to the T junction and from there back to both side's fuel delivery units (not exactly back into the pump).
 

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Ok I see. You’re like me then just playing :)
Which engine do you have?
And which repair manual?


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Discussion Starter #20
I have the BMV engine, the 3.2L 6 cyl 177 kW one.
Since this fuel supply system is returnless (no vacuum driven regulator), and there doesn't seem to be a fuel pressure sensor for the ECU (as far as I am aware), how does it control the constant pressure if it needs to start and stop the pumps often?
 
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