SAI and N249 Removal

In a fuel injected car, there are some moments the emissions are disregarded. Normally is the warming up period and in some cases when you give full throttle. The SAI pump and EGR are just gizmos to make the car greener.

You have to remember the lambda sensors only work when they are hot and they are responsible to help the engine with AFR.

The N75 is one other failsafe gizmo. It works blocking the pressurized air to the WG, therefore we have boost. If you disconnect it, the air will pass through it opening the WG.

What I will do. I will recalibrate the WG. I will tighten it more to open after 1,4bar.
One other option it to use a MBC. It will work fine too.

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Originally Posted by noone

I'm not sure about removing the SAI as the return air is expected on startup, surely this would mess with the AFR for the first 1 min?

As for bypassing the N75, unless you are using a MBC, how would you control the wastegate?

I'm not sure if these would work too well for normal driving, as your car is set up for track use, maybe a little different?

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Originally Posted by vwthunder

Yeah that is what i was thinking

I have a manual boost controller sitting here, will put it in when i have time and hopefully see a spike over 17.6psi, which is what i am getting according to logging

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All threads I've read on MBC's for the 1.8T's report partial throttle issues with MBC. I drive in too much traffic to want the hassle of throttle abnormalities...

Can someone help me understand how the vacuum works off the manifold? Is this vacuum consistent or does it fluctuate with the revs?

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Originally Posted by noone

All threads I've read on MBC's for the 1.8T's report partial throttle issues with MBC. I drive in too much traffic to want the hassle of throttle abnormalities...

Can someone help me understand how the vacuum works off the manifold? Is this vacuum consistent or does it fluctuate with the revs?

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Have a think about how an engine fills it's cylinders. Suck, squeeze, bang, blow. You get vacuum when the pistons are going down the bore with the inlet valve open.

On a turbo car, this would be true during off boost conditions and very small throttle openings. When you open the throttle, boost rises and you have positive pressure in the manifold.

When you close the throttle during a gear change or over-run, there will be positive pressure between the turbo and throttle body, which gets vented back to the inlet. In the inlet manifold, there will be a vacuum as the pistons suck against the butterfly.

If you have a boost gauge you can see this easily.

Gavin

I disconnected all solenoids (n249, n75 and n112) and the SAI pump.

I’m using a MBC! I remembered I had one!

I've got frustrated, the electronic throttle hold the engine. I will need to use transistors.

On the other hand I finally can see the engine.

I connected the solenoids and give one other shoot.

The results were impressive. With 1,3bar now I have more torque then before.

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Originally Posted by h100vw

On a turbo car, this would be true during off boost conditions and very small throttle openings. When you open the throttle, boost rises and you have positive pressure in the manifold.

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Thanks mate, thats what I expeced, but was not sure. I assume that bypassing the N249 would make the vacuum control on the diverter obsolete as well...

I bypassed my N249 today, I had tried it ages ago, but did not notice any improvement.

Big difference today, boost comes on earlier and stronger. I'm going to keep it like this for a while to see if the ECU adapts to the difference and tries to compensate by bleeding my boost somewhere else or delaying when it comes in (altering the N75 use).

noone, did you just do the typical method of looping the N249 onto itself, then running the diverter valve straight off the plenum, or did you go to the trouble of removing the N249 entirely with resistors etc?

Just taking the diverter vac feed from the manifold tubing (using the first T piece) and looping the pipe for the N249 back on itself.

No codes, etc.

I am interested in getting rid of the rest, but don't want codes coming up all the time. Maybe if I get a retune down the track and they can remove this function I will do ii all...

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Originally Posted by noone

Just taking the diverter vac feed from the manifold tubing (using the first T piece) and looping the pipe for the N249 back on itself

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I've just done this as well. Do small cable ties (2.5mm) work ok as permanent replacements for the single use metal clamps on the vacuum lines? Or do you use something else?