Removing N249 valve - How To Guide

OK, here's a guide how to remove your N249 valves. As in a previous thread of mine, i detailed what does the N249 valve do, but here's it again:

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).

Shopping List (what you need):

- Some (50-80cm) 4mm ID vacuum line.
- 1x 4mm T piece
- 4mm Check Valve which can be reused from the original OEM setup
- 9 x 270Ohms 5W Resistors (the bigger surface the better)
- Small test/breadboard
- 1m wire (2core)
- Zip ties (big & small), masking tape
- Drilling machine, 1mm thick alu plate
- Soldering ability/skill

This is (below) how the original vacuum reservior, N112 (Secondary Air Injection Solendoid) and N249 (Turbocharger Bypass Valve) looks like on the Mk3 Ibiza 20VT. The entire "system" has been removed, but some part of this has to be reused! I've just simply cut the vacuum lines, disconnected electrical plugs, and unscrewed screws.



As the first step, we have to put the N112 back as this controls the combi valve, which opens the head for the Secondary Air Pump to be able to pump air into the exhaust. The combi valve is operating with vacuum (just as the DV), and N112 opens it (to the command of ECU) during cold starts only. We want to keep this feature (as it has nothing to do with performance) so we have to put the N112 back to its original place. Get it out from the original setup. An appropriate sized alu plate has to be cut, bent and drilled, which is then secured on the valve cover using the screws which was holding the original stuff (seen above). I had to use some washers too, because the screws were a bit long (one screw was taken out from the original assembly, too - you'll see). The Sec Air Solendoid (N112) is secured on this alu plate with 2 bigger zip ties. To hook up the N112, connect the combi valve line (with the silvery heat shield) on top - just as it was connected defaultly. Leave the gray plastic cap on the left side on. That port is used to release vacuum from the combi valve (closing it), so do not clog it. The cap is just used to prevent bigger dirt particles to enter into the N112 & combi valve, when vacuum is "released". Now that two ports are connected (cap & combi valve), you have to connect the vacuum source to the third (horizontal, right side) port. It is absolutely critical that no boost can enter the N112, so place a check valve (salvaged from the original setup) in the right direction (you can suck air out from it, but cannot blow into) before the solendoid (just as on the picture below). Plug the N112 electrical connector in, too. If you are ready, all 3 ports of N112 will be connected, one still unhooked, with a check valve on it.

Now hook the DV up, just lead some 4mm vacuum hose from the topmost nipple of the DV to the valve cover, OR just simply reuse the original DV line. Use the T piece to connect the unhooked N112 vacuum line (with the check valve on) and the line from DV with the vacuum/boost source from the manifold. Zip tie every connections/lines, so they can't move, can't be blown.

This is how it should look like (except for the N249 plug):


Theoretically you have now removed the N249 valve (N112 has been reinstalled, remember?), you could try the car, BUT the electrical plug of N249 is not connected, since there is no N249 anymore. The ECU would detect this fault and the Check Engine Light would illuminate. You have to trick the ECU, so it thinks there still is an N249 valve connected.

To do this, i have measured the resistance of the N249 valve, which is 30Ohms. If you plug anything on the N249's electrical connector which has 30Ohms resistance, ECU would think there's a solendoid there (how silly ). The resistance is just one parameter, there is an other very important one, the load. On 14V, a 30Ohms "thing" will flow nearly 0.5A through. If you would lead 0.5A through a small 30Ohms resistor it would immediately overheat, even burn your hand and things near to it. Therefore, you have to buy a big surface, big load (40-50W) 30Ohms resistor, OR use more resistors, so the surface will be big enough to be able to dissipate heat. I have connected 9 pieces of cheap 270Ohms 5W resistors paralelly on a breadboard and used this "resistor bank" as a 30Ohms 45W resistor. Sadly i have no picture of this, but the formula is very simple. The resulting resistance will be Resistance/Nr of resistors used. For example i've used 9x270 5W which will be equal to 270/9 = 30Ohms 5*9= 45W. It is quite big and oversized so it will not burn anything, it just gets nice warm (30-40C). You may use any setup, but be sure not to use less than ~30W, and make sure it has got a resistance of 30-33Ohms.

This is one of the the cheap resistors i've used. Bought 10pieces for ~1 EUR, this one i have left. They were just simply connected paralelly (NOT SERIALLY!) on a breadboard cut to the right size. A long wire has been soldered on the two ends of this resistor bank and all this has been covered with black masking tape



The resistor bank is then secured to a loom in the car i've found and is hidden, so it is not visible to the unaided eye at all.



I did not cut the original N249 electrical plug off the stock loom (and i suggest this for you too). I've just naked some wire on the other end of the resistor cable, applied some tin on it with the soldering iron, so it got hard and stiff. I could plug these hard wires into the stock N249 plug, and secured them with masking tape well. Be careful and make sure they won't/can't come out and touch themselves! This solution seems to work well for me and it costs nothing.

Practically you have now completed the task! I have got this setup working now on my car for almost 2 months without any problem. Have Fun!

Questions?

Oh yeah, as with anything else, no responsibilities taken!

REMARK: This writeup (as you've probably noticed) was carried out on an Ibiza. The vacuum reservoir, N112, N249 on Leons are located elsewhere, but they look and work the same, so you probably can find them .

Here's a diagram of the resistor bank.

Cheers

chriskaven said:

Have I understood correctly??

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Yes. But it seems that ECU is fiddling with the DV a lot more times than i originally (or anybody else) thought! Older 1.8Ts dont even have got N249, DV is fed directly from manifold. The problem is, that if ECU decides to open the DV for a short time to settle the boost (lets say by less than 0.1 bar only), the DV will not close that fastly/promptly back (since boost is pushing the piston/diaphragm) and you'll lose a lot more boost than intended/expected. This is just a theory though (slower DV closing under boost), but there is definitely a change in smoothness by doing this mod.

BTW: Just simply unplugging the N249 electrical connector (and letting the CEL to come on) is not (!) yielding the same result as completely removing the valve! Interesting.

Glenn said:

Could this be used as part of a knock reduction strategy?

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I would not think. Detonation may be precisely controlled by the distributorless ignition system.

Glenn said:

The engine designers know more than we do - new product features are not just added 'for a laugh'.

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Yes, you're absolutely right - but we (most of us) are doing mods on our engines and judge the stock setup. ECU still can lower the boost using N75 valve and/or close throttle plate any time it wants. Limp mode also can be activated any time - still too much ways for the ECU to decrease performance .

I guess you mean that black reservoir with "vacuum store". N112 works only and exclusively at cold starts (when engine is really cold, lets say starting up for the very first time a day). It has absolutely no effect after warmup and while cruising. It does not need the black cannister/reservior at all, though you have to provide the N112 with vacuum (only) - that's why the ckeck valve there AND make sure you don't press WOT right after coldstart (so vacuum is available from the engine), but who does it?!

Keeping the reservior for the N112 has no adverse effefcts at all, but it is not neccessary - i removed it because i did not want to see it there . One of my coils went and i am waiting for the others too. I'm carrying a spare coil in the boot, without the reservior i can replace a bad coil any time without that reservoir.

Keeping the reservoir for both N112 and DV without N249 is impossible! Vacuum will leak out from the reservoir without the N249.

I suggest you to scan your codes to see why does it enter limp mode.

Ahh now i know what you mean!

The wastegate actuator (brassy can) of the small K03 on the Ibiza has two nipples facing opposite each other. This is the only K03 which has two nipples, so the Ibiza is unique in this manner.

One is controlled by the N75 where air is "pushed" into it to open wastegate and the other one is fed by the N112 (tapping the line from the N112 to combi valve using a T). When N112 opens the combi valve (with vacuum) for the Sec.Air.Pump to be able to push air into the head/exhaust, it will simultaneously lead vacuum into the opposite side of the wastegate actuator (through T) which will "SUCK" the wastegate open. This will result in no boost at all until the N112 (and head for the airpump) is opened. As long as the warmup process finishes, N112 will release vacuum from these lines to the atmosphere through that little cap on the N112 - do not clog that cap/nipple completely as your head and wastegate will stay "sucked" opened - been there done that. So practically N112 is connected to the wastegate, yes (you both have right) but it does not control boost al att! It is just making sure that the turbo cannot boost during coldstart. It is a nice feature but completely unneccesary i think, no other 1.8T or 2.7T or anything has this feature at all.

Since the combi valve and the other side of the actuator is fed from the same line, it is impossible that the N112 would regulate any boost, otherwise it would affect the combi valve too. Combi valve is kept closed after the warmup!

You say that valve at the back (N112) is connected to the manifold. That is right, but it needs the check valve/one way valve, so boost CAN NOT enter it. Place the OEM check valve with the white part facing the N112. The line to the DV must not have any check valves before! It has to be fed directly from the manifold, so boost and vacuum both can enter the DV!

Just check out my photo above. I am having a line coming from the manifold which can supply both boost and vacuum (depens which one is available). Then a T comes, one line goes to the DV directly (without anything), and the other line goes the the N112 with the check valve in between. That is all, if you hook this way up, it will work! You dont need the black vacuum cannister either (it is for the N249 not for N112).

Yes it would not make any difference. If you're still in limp mode, it is not because of the N112. I'm wondering what your problem could be, if you say it's connected like mine on the picture above, then it should work.

ICE MAN,

I would not suggest this mod to anyone who is not familiar with the engine and who's not taking some peek on things once a while, just to be on the safe side. I dont think that removing these parts would have any really bad effects on the engine. Running high boost and lean mixture may have though.

Any questions are welcome