Audi s8 d3 5.2 litre v10 £3.5k

[S81]

When you remove the oil cap on the engine i know my car goes of idle ,the chap i know who does a lot of engine work says its to do with it being a positive pressure engine ,i'm sure someone here will know exactly what that means

[Furryhobnob]

Originally Posted by IT

You have PM

Have replied Ian, thanks

[MikkiJayne]

Originally Posted by S81

When you remove the oil cap on the engine i know my car goes of idle ,the chap i know who does a lot of engine work says its to do with it being a positive pressure engine ,i'm sure someone here will know exactly what that means

Positive Crankcase Ventilation (PCV). It's a bit of a misnomer tbh because intake vacuum is applied to the crankcase to suck out any combustion gases which escape past the piston rings. That makes the pressure in the crankcase negative at low engine load, so I guess it really means 'we definitely are ventilating the crankcase' The breather pod cuts off the vacuum under heavy load or wide throttle openings, since there is no vacuum to do anything, and high load on the engine seals the rings up more so there is less blow-by to recover.

When you remove the oil cap, you basically allow a load of unmetered air in to the engine via the breather pod, which upsets the combustion because the ecu doesn't know about it and so struggles to compensate.

If you remove the cap and it doesn't affect a bad idle then you have an air leak somewhere. The first place I'd look with this one is the inlet manifold gaskets, since its been off previously. Not sure how complex the vacuum system is on the V10, but thats somewhere else to look.

Also, someone please buy this because the price is verging on me buying it just for the engine and I have enough projects already!

[Furryhobnob]

Originally Posted by MikkiJayne

Positive Crankcase Ventilation (PCV). It's a bit of a misnomer tbh because intake vacuum is applied to the crankcase to suck out any combustion gases which escape past the piston rings. That makes the pressure in the crankcase negative at low engine load, so I guess it really means 'we definitely are ventilating the crankcase' The breather pod cuts off the vacuum under heavy load or wide throttle openings, since there is no vacuum to do anything, and high load on the engine seals the rings up more so there is less blow-by to recover.

When you remove the oil cap, you basically allow a load of unmetered air in to the engine via the breather pod, which upsets the combustion because the ecu doesn't know about it and so struggles to compensate.

If you remove the cap and it doesn't affect a bad idle then you have an air leak somewhere. The first place I'd look with this one is the inlet manifold gaskets, since its been off previously. Not sure how complex the vacuum system is on the V10, but thats somewhere else to look.

Also, someone please buy this because the price is verging on me buying it just for the engine and I have enough projects already!

If homer simpson doesn't have it then someone has already dropped me a pm saying they will take it, I'll just be glad it's going to someone willing to give it some tlc and get it singing again, cheers

[Furryhobnob]

Well I've certainly garnered alot of interest, in people wanting to buy and others with advice of what the issue could be, because of this I'm going to withdraw it from sale for the time being and try and source the idling issue myself.
I feel this is the right path to go down right now as there's not many of these around and it would pain me to see it stripped or used as a donor without me first trying, hope everyone interested understands. Regards

[tonupkid]

Once everyone else has done the heavy lifting for you, you've swivelled

[Furryhobnob]

Originally Posted by tonupkid

Once everyone else has done the heavy lifting for you, you've swivelled

What do you mean Tony? Heavy lifting in what sense?

[roberto]

2nd dibs please ill take it

pm sent

[homer simpson]

Originally Posted by roberto

2nd dibs please ill take it

pm sent

I there were a few in the queue ahead who would have purchased this had it not been withdrawn.

I was due to collect this on the weekend but it was withdrawn from sale, which I understand, we are all entitled to change out minds. The car is cheap but can also become a money pit to put right.

Even though I would've loved to purchase this, I think it's fair and great that furryhobnob is going to have a crack at it. Forums are all about helping other members and I'm sure it can be sorted proving the OP has time and budget to sort it. Others may have a different view and they are entitled to it. I'll await the fix thread, let's see if we can help out and solve this one

[roberto]

yes no problems hope he fixes it..

i was going to 3.0tdi it LOL