N249 Bypass guide LCR

[rsmith]

Ladies and Gentlemen,

I did the below quick guide to bypassing the N249 value, there may be other ways but i think this is the easiest, i created this guide for vagdrivers.net but as there are still requests on here so i decided to post it over here too..

I already posted my graphs showing my boost curve from before and after this mod, so it is well worth while IMO, in addition I notice the Dump reaction is quicker and throttle response has some improvement, you also get some more chatter when you let off the throttle.
Before after graphs http://www.seatcupra.net/forums/showthread.php?t=215185&highlight=n249
Proceed at your own risk!

Tools needed.

4mm silicon vacuum hose, i used fuel line hose as it is more commonly available
5mm hose connector * 1, ( I used 5mm copper pipe as it is stronger)
Long nose pillars
Cable ties
20 min of free time.


Step 1

Example of hose locations and hoses to be removed, also you can see in yellow where the new hose will go.

Step 2

Remove the 2 hoses pointed out in the diagram from the N249, the clips are stubborn so you will probably have to break them.

Step 3

Remove other end of the hose from the Diverter value, as below, the hose from the N249 to the DV is totally removed now, store this in a safe place in case you need it in the future.

Step 4
We will now join the new piece of 4mm hose from the DV straight to the hose we disconnected from the N249, cable tie it and cut excess cable to clean it up a bit.
That’s it your done.

Do not block off the hose connectors that your removed, some people have tried it and had negative performance as a result

 

[Richie-LCR]

Well done mate that should make life easier for some folk, I was thinking of doing a guide today but never had the time

 

[rickyb90]

I've read through your guide and the pictures makes it a neater way of explaining how to bypass than the other threads I've seen. They're ok but sometimes a pictures tells a thousand words

 

[Cupra Ross]

Excellent guide for the BAM and AMK owners. Well done sir!

Just one question, where does the N249 hose that goes off to the rear of the multiplug go to? I'm guessing its the N112 feed?

 

[R Power]

well done mate, defo best guide ive seen. im going to attempt this myself, just to clarify if im reading it right, the hose that goes from DV to N249 u take off, as well as disconnecting the hose on t-piece, then just get a 4mm pipe and connect from DV to that pipe which one originally on the t-piece, so you go around that valve? and leave the ports unblanked? so simply one hose and a connector?

 

[james walker]

just need one for the auq owners now boyos.... or is it the same?

 

[adam cupra 20vt]

just need one for the auq owners now boyos.... or is it the same?

Here you go mate Cupraross done one for the AUQ I got the bits ordered to do mine this weekend

http://www.seatcupra.net/forums/showthread.php?t=195511&page=5

 

[paul-murphys]

good guide will be giving it ago

 

[james walker]

Here you go mate Cupraross done one for the AUQ I got the bits ordered to do mine this weekend

http://www.seatcupra.net/forums/showthread.php?t=195511&page=5

yeah just seen that one....

got the bits ordered now, so ill get it done asap, hopefully thursday.

 

[rsmith]

well done mate, defo best guide ive seen. im going to attempt this myself, just to clarify if im reading it right, the hose that goes from DV to N249 u take off, as well as disconnecting the hose on t-piece, then just get a 4mm pipe and connect from DV to that pipe which one originally on the t-piece, so you go around that valve? and leave the ports unblanked? so simply one hose and a connector?

Yeap thats it, no great mystery to it.

 

[rsmith]

Excellent guide for the BAM and AMK owners. Well done sir!

Just one question, where does the N249 hose that goes off to the rear of the multiplug go to? I'm guessing its the N112 feed?

Cupra Ross, according to the below hose diagram from vagdrivers.net it does appear to be the N112 feed

i wonder can anyone double confirm this?

 

[Cupra Ross]

Excellent find, many thanks.

The only thing that was stopping me from completely removing all boost/vac connections to the N249 was the uncertainty of what will happen with the SAI combi valve. From that diagram it appears to be vacuum actuated with no boost related function, so if I simply plug the hose to it, it will not stick open.

Thanks.

 

[Witalik]

and also does it generate any fault codes on ur leon ?

 

[rsmith]

and also does it generate any fault codes on ur leon ?

I have had zero faults on my ECU from this mod and i scan my car every other day.

 

[Muttley]

Cupra Ross wrote

The only thing that was stopping me from completely removing all boost/vac connections to the N249 was the uncertainty of what will happen with the SAI combi valve. From that diagram it appears to be vacuum actuated with no boost related function, so if I simply plug the hose to it, it will not stick open.

The N112 is electrically actuated and uses vacuum to open the combi valve for a couple of minutes after a cold start, allowing the secondary air pump to blow air from the air filter into the exhaust system. If you plug the N112 your secondary air system will stop working.

There are no boost connections to the N249. The only actuator that has a boost connection is the N75 (and only on turbo-petrol engines).

 

[rsmith]

Cupra Ross wrote

The only thing that was stopping me from completely removing all boost/vac connections to the N249 was the uncertainty of what will happen with the SAI combi valve. From that diagram it appears to be vacuum actuated with no boost related function, so if I simply plug the hose to it, it will not stick open.

The N112 is electrically actuated and uses vacuum to open the combi valve for a couple of minutes after a cold start, allowing the secondary air pump to blow air from the air filter into the exhaust system. If you plug the N112 your secondary air system will stop working.

There are no boost connections to the N249. The only actuator that has a boost connection is the N75 (and only on turbo-petrol engines).

I thought only LC's had a secondary air pump?

 

[Cupra Ross]

The N112 is electrically actuated and uses vacuum to open the combi valve for a couple of minutes after a cold start, allowing the secondary air pump to blow air from the air filter into the exhaust system. If you plug the N112 your secondary air system will stop working.

This is what I'm having trouble understanding. I've now totally removed my N249 and N112 from the intake manifold. Guess what, my SAI system is still working!!!

I've left both valves electrically connected only. This is to stop fault codes being generated.

There are no boost connections to the N249. The only actuator that has a boost connection is the N75 (and only on turbo-petrol engines).

N249 has a direct boost/vac connection from the intake manifold. Its nature is dependant on the position of the throttle butterfly.

 

[gb]

ive done mine a bit diferent ,done the first bit the same then joined the hoses together with the conector then the new bit of pipe straight into the top of the dv and had no problems what so ever

 

[Muttley]

Cupra Ross wrote

This is what I'm having trouble understanding. I've now totally removed my N249 and N112 from the intake manifold. Guess what, my SAI system is still working!!!

I'm sure that your secondary air pump is still coming on, but is the combi valve opening, is the air getting into the exhaust? How can you tell?

N249 has a direct boost/vac connection from the intake manifold. Its nature is dependant on the position of the throttle butterfly.

Hmmm. Strictly true, but the dump valve is pressure-sensitive and is activated by vacuum, not boosted pressure. As far as I can tell, that is what all the complicated plumbing is about. The N249 system connection is not so much a vacuum source as a pressure sensing connection.

The N75, on the other hand, in this system, uses boost pressure, tapped from the charge pipe downstream of the turbo, to open the wastegate. This is unlike the case in, say, the diesel engines, where the N75 uses vacuum to control the VNT vanes.

 

[Cupra Ross]

This is what I'm having trouble understanding. I've now totally removed my N249 and N112 from the intake manifold. Guess what, my SAI system is still working!!!

I'm sure that your secondary air pump is still coming on, but is the combi valve opening, is the air getting into the exhaust? How can you tell?

The exhaust note from a full Milltek system under SAI is very different from that produced in the absence of SAI, believe me. I'll check tomorrow morning but what you're saying makes a lot of sense.

N249 has a direct boost/vac connection from the intake manifold. Its nature is dependant on the position of the throttle butterfly.

Hmmm. Strictly true, but the dump valve is pressure-sensitive and is activated by vacuum, not boosted pressure. As far as I can tell, that is what all the complicated plumbing is about. The N249 system connection is not so much a vacuum source as a pressure sensing connection.

In its un-bypassed state, the N249 is just that, well a conduit in the vacuum source if you like. It supplies vacuum to the top of the DV, lifting the diaphragm or piston and venting boost back to the turbo intake pipe. This vacuum comes from the intake manifold or the vacuum reservoir via the N249. When under throttle, the DV is held shut by 2 things, a spring and boost pressure.

The N75, on the other hand, in this system, uses boost pressure, tapped from the charge pipe downstream of the turbo, to open the wastegate. This is unlike the case in, say, the diesel engines, where the N75 uses vacuum to control the VNT vanes.

Diesels have a vacuum pump for this purpose due to their lack of a conventional throttle. The intake system on a diesel is incapable of creating vacuum in the way that a petrol engine does. The N75 on a diesel is there to control blade pitch as you say but a diesel cannot technically overboost. A diesel engine takes a full charge of air regardless of the position of the accelerator pedal. Petrol engines are completely different in this respect.