SAI issues, partial delete?

[amdeman]

Hi team, before it's suggested, I HAVE tried the search function.
When starting the car in the morning it sounds like a large vacuum cleaner going under the bonnet; from research it seems highly probable that it is the SAI system. Other than sounding like a Hoover, is there a chance that it is also causing performance issues?
By unplugging it, there will be warnings, and flashing lights, possibly a limp mode; unless there are resistors in situ.
If the ECU is coded to not look for the sensors, could the SAI system remain, physically, in place without causing any further issues; or will it mean that boost could be lost?
TIA.

[h100vw]

Hi team, before it's suggested, I HAVE tried the search function.
When starting the car in the morning it sounds like a large vacuum cleaner going under the bonnet; from research it seems highly probable that it is the SAI system. Other than sounding like a Hoover, is there a chance that it is also causing performance issues?
By unplugging it, there will be warnings, and flashing lights, possibly a limp mode; unless there are resistors in situ.
If the ECU is coded to not look for the sensors, could the SAI system remain, physically, in place without causing any further issues; or will it mean that boost could be lost?
TIA.

SAI can't be fixed with resistors as the ECU looks for the flow. It needs fixing in the tune.

No limp mode just the CEL to give you a sun tan.

Gavin

[amdeman]

SAI can't be fixed with resistors as the ECU looks for the flow. It needs fixing in the tune.

No limp mode just the CEL to give you a sun tan.

Gavin

Thank you.
If the SAI is physically left in place, and the tune modified, is there a potential for any issues with power, i.e. bleeds boost?

[h100vw]

Thank you.
If the SAI is physically left in place, and the tune modified, is there a potential for any issues with power, i.e. bleeds boost?

You could leave it all there but it's extra weight. I'd give you a blanking plate and you can chuck it all in the nearest bin. No dramas with lost boost.

Gavin

[amdeman]

You could leave it all there but it's extra weight. I'd give you a blanking plate and you can chuck it all in the nearest bin. No dramas with lost boost.

Gavin

By leaving it there, other than the bulk / weight there are no issues with redirected air or boost blow by?
The main reason is that I'm lazy, and it will cost to have the system removed (I am 'frugal').

[h100vw]

Take it out yourself mate. It's not rocket science, it's guy stuff!!

[amdeman]

Take it out yourself mate. It's not rocket science, it's guy stuff!!

As much as I enjoy getting my hands dirty, I have a fear of 'car-no-go' syndrome; caused by a) not following instructions, or b) stupidity (see a).

[h100vw]

As much as I enjoy getting my hands dirty, I have a fear of 'car-no-go' syndrome; caused by a) not following instructions, or b) stupidity (see a).

I could do some pretty precise instructions for you if you want.

Gavin

[amdeman]

I could do some pretty precise instructions for you if you want.

Gavin

That would be awesome! Thank you.

BJX specific?
One of the main reasons for lack of enthusiasm is that with all of the tutorials online, ensuring that it is actually for my chassis / engine is crutial to success.

[h100vw]

That would be awesome! Thank you.

BJX specific?
One of the main reasons for lack of enthusiasm is that with all of the tutorials online, ensuring that it is actually for my chassis / engine is crutial to success.

I could do as, I have a Polo but all 1.8Ts of that era are the same make up.

The worst part, if there is one is that you need to partially drain the cooling system to fit the blank. One of the bolts that holds the combi valve tower is right behind a water outlet on the side of the head.

That's probably the worst part. I did one in the street outside my house a while back for ST165.

There's a drain tap on the radiator on the passenger side. Drop the coolant into washing up bowl, ask your mum first, then you can reuse it. I do this as there's no where local, to dispose of it in an environmentally way.

You need an odd 13mm nut to retain the dipstick tube bracket. I can dig one out for that and send it too.

Gavin

[amdeman]

I could do as, I have a Polo but all 1.8Ts of that era are the same make up.

The worst part, if there is one is that you need to partially drain the cooling system to fit the blank. One of the bolts that holds the combi valve tower is right behind a water outlet on the side of the head.

That's probably the worst part. I did one in the street outside my house a while back for ST165.

There's a drain tap on the radiator on the passenger side. Drop the coolant into washing up bowl, ask your mum first, then you can reuse it. I do this as there's no where local, to dispose of it in an environmentally way.

You need an odd 13mm nut to retain the dipstick tube bracket. I can dig one out for that and send it too.

Gavin

That would be awesome, thank you.

[Dugle]

I have a question, what exactly is the SAI supposed to do?
As best I can tell it removes air from the cooling system.

As for the low flow CEL, the only way the ECU can tell if there is low flow from the SAI, is a resistance change from the pump.
There are no other sensors, that I can see, that could detect a change in air flow from the pump.

Please feel free to correct me.

Cain.

[sambb]

I think the ECU needs to see the mixtures lean out as the air is pumped into the exhaust manifold. It might make calcs from that and the elevated idle to work out whether or not the cat temp is high or not?

[Dugle]

I think the ECU needs to see the mixtures lean out as the air is pumped into the exhaust manifold. It might make calcs from that and the elevated idle to work out whether or not the cat temp is high or not?

Generally on any pump the large opening is the inlet, if this is the case for the SAI pump, then it means that it sucks air from the air box and feeds it to the combi valve.
The combi valve has nothing to do with the exhaust manifold, it is part of the cooling system.

I am beginning to reallise that of all that I have read, nobody knows what the SAI really does.

Cain.

[sambb]

my understanding is that on cold start, the SAI solenoid is activated. At the same time the SAI pump starts. The energised solenoid gives the inlet manifold vacuum which is about 20in/hg a pathway to the top of the combi. This vacuum will suck on the top side of the combi diaphragm drawing it up. This creates a pathway then for filtered air from the airbox to be drawn through the SAI pump and then into the top of the combi. This uncombusted air then travels down the combi tower into the side of the head. There is a common channel in there that gives the uncombusted air access to each of the exhaust runners. When this air mixes with the combusted exhaust gases it causes the exhaust temps to rise quicker than if they had just been normal rich startup gases. This elevated temperature forces the cat to very high temperatures very quickly allowing it to reach its operating temp asap. That way when you drive off,even though the engine may barely be off the needle temp wise, the car will be running as clean as it can be with respect to emissions. If the feedback loop which I assume comes from the O2 sensor, doesn't see nice lean mixtures (like the ones that give rise to hot exhaust temps), then it assumes the SAI has failed.
Basically the engine will itself will have optimal startup mixtures, but since these are not necessarily the correct mixtures for clean startup emissions, the air injection necessary for cat pre heating happens after the combustion process.

PS lots of cars actually have the air injection port on the cat itself. Diesel DPF filters work in a simialr way. They'll either run the engine very lean if you're ona long lean cruise down the highway or inject air directly into the DPF to basically fire up a furnace and bake off all the particulate matter the filter has caught - same principle.