Removing N249 Valve From a 20vT

This is a work in progress to collate all the information I have gained about the removal of the N249 valve from a 20vT engine. Locations for these differ on the VAG models so lets start with the facts.

N249 is controlling the DV (Dump Valve). It is installed between the intake vacuum source and DV itself. When no current is switched to the N249 (default state), the DV will get vacuum or boost from the intake manifold. This is how almost ALL turbo cars are worknig. When shifting gears, you let off throttle, TB closes and vacuum is generated which can open DV to vent boost (which cannot enter engine, because TB is closed).

On never 1.8Ts (2000+) they introduced the N249 (along with lots of other stuff) which is a possibility for the ECU to open the DV any time (!), even during full throttle/acceleration. When the engine is running and turbo is boosting, there is no vacuum generated, but to open the DV (which is mechanical), vacuum is needed. This is what the black vacuum reservior on top of the engine is used for. When idling, shifting, etc - so when vacuum is available, vacuum is led into this reservoir from the intake manifold and kept inside using a check valve (white/black), so when boosting again, vacuum will stay there (air cannot enter into the reservoir).

When ECU wants to open DV durnig full throttle/acceleration, simply "energizes" N249, which will "de-select" the DV from the intake manifold (boost), and "switches" it onto the vacuum reservior. The vacuum in the reservoir will open the DV instantly and release your boost, which, in most of the cases (tuning, etc) is not that highly required . In the case ECU sees a little overboost problem, it can turn N249 on/off repeatedly for very fast (just as N75 is working), which will open/close DV all the time, trying to settle (lower) the boost level.

PROs: By removing N249 valve, you can prevent this bad habit of the ECU, and by removing N249 valve, you are removing an approximately 2mm narrow bottle neck restriction (ID of the N249 valve) in the line to the DV, which will result in a somewhat faster DV response. I am using the stock bosch DV, but it feels just as good as an aftermarket DV with N249 (restriction) inline. Boost curve is smooth and progressive.

CONs: Boost overshots/spikes may grow higher, especially in high gear/low rpm situations (using the small K03), which can result in a leaner condition (for the moment). These spikes depend on N75 type, wastegate setting and software programming, but they usually don't last long (0.5-1s max). In the case these spikes are very high (car enters limp even), minor adjustment on the wastegate can be done. Ibiza engine covers cannot be used anymore (by removing the accessories above, two mounting points of the cover are removed aswell).

The following post discusses the removal of the plate that holds the n249 valve on the MKIV 20vT.

Plate removal



The N249 valve is the one in the middle (unless all the diagrams are wrong....), the following picture shows the parts and how to bypass it. Some people believe that only by passing the valve completely will the effect of its operations be completely removed. Once it has been bypassed the resevoir on top of Cap 4 (MKIV Golf) can be removed.

The gold covered valve is the N112, that controls the combi valve, which opens the head for the Secondary Air Pump to be able to pump air into the exhaust. If you are bypassing that as well then we will make another guide for it.

Bypassing the Valve

I am going to reuse the white t-piece on the left, leave the connection to the left that goes correctly into the one way valve. On the other side of the valve I will disconnect the black rubber t-piece and then connect a hose from the one way valve to the bottom of the gold N112. I will then leave the pipe coming back out of the valve towards the thinner (top) OEM tube. That will be a complete circuit from the T Piece, through the one way valve to the N112 in the correct direction back to the pipe that goes to the secondary air intake valve (N112).

Back to the white T piece, I will disconnect the black right hand side that goes to the N249 valve and pipe this back to the Diverter valve. The system now needs a vacuum source so let us connect this back to the inlet manifold as it previously was.

This way I am not going to actually do anything other than bypass the valve and for now use mostly OEM kit to ensure it can be put back together should I need to later.




references
Removing N249 valve - How To Guide SEAT

so how do u remove it from the system then ?

excellent bit of info calimori!

ive done mine and not had any probs! makes engine bay look neater too

Sorry, ran into a little work and had to stop .
That was the intro so I don't lose it.
Next comes a whole load of pictures of the engine with the vacuums all plotted out in different colours.

Gricey, your solution works but it can be made a little better and then be able to remove parts so that you free up some space and even clean up the whole plate in front of the intake.

I will pull together all the pictures but some others info is here

The top left shows the various re-route and bypasses that can be done, the bottom right shows the original routing on most 1.8 20vT engines:

think this may be a trial and error one sunday job

Yep, from what I can tell, you car still has the valve connected, you have bypassed the vacuum reserve and therefore the valve can not work correctly but it is still in the circuit. Some people report that it being present can effect the vacuum but I am unsure why.

I am surprised to see that the secondary air system also is connected to the vacuum system...

I plan to do mine and take some pictures....

gricey is yours like mine? with just the connector left or is yours still original? i cant remember.

calimori, that may be why my car sounds like a hoover when its cold! for about 30 seconds

nah the hoover noise is a seconday air pump designed to pre warm the cat before u start driving to make it more effecient on choke

oh right, do you get it too then? these germans think of everything dont they!

yeah basically if it sounds lioke a tank u can remove it drill out the rivets add a sealant then bolt it back together and replace it , basicall the plastic warps and splits on the seal tbh i wanna get vag com (full version) and switch the bloody thing off as i dont have a cat any more

cali is prob your man then! ive got vag com too (full version) its older than calis though

wikid mine is unregisterd dooin my head in lol

Yep, the seconday air pump is making that tank noise. Because you have disconnected in the intake when you replaced the air-box, you are now sucking from the engine bay.
However, the diagram shows that this pipe goes into 20 and then on to 12, 12 also uses a vacuum supply off the manifold. Get a leak here and you might again end up with poor boost.

It weighs a bit and takes us space so it would be interesting to see a car with it removed.

cali youve just given me an idea........ hmm the next guide.....

Keep them coming mate, you are a star, that is why you sparkle....

OK, I have updated the main thread.

There are two ways to do it, first tap into the FPR (Fuel Pressure Regulator) with a T Piece and run your DV from there. This requires that you also cap off line that the DV was using.

Or you plumb around the N249 valve...

I have now given info on how to do this now, the FPR idea will work just as well.