SAI issues, partial delete?

[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.