Modifying the Afterrun Pump control on S4/RS4

[Dippy]

Instead of using a turbo-timer to idle the engine, a better solution is to force on the afterrun pump on the S4 and RS4.

For those who don't know, the S4/RS4 turbos are water-cooled. However when the engine is off, so is the water pump.

However the Audi designers realised that if the turbos are very hot, the water could boil, creating air pockets which in turn could create dangerous hot-spots. So they put a temperature sensor in the water line, so if the water is very hot, the ECU will turn on the electric cooling fan and also activate the afterrun pump. This pump keeps the water flowing thru the turbos, but in the opposite direction, so that the air bubbles are dispersed in the engine water jacket.

Now the temperature this happens at must be very high as the pump is rarely activated. So to make this system more useful, if the sensor could be fooled, the pump would run for a time after the engine is turned off, cooling the turbos!

Such a mod is really easy. The sensor is a VFC, so by wiring the VFC from a turbo timer in parallel with it, the turbo timer can force on the pump. Unfortunately most TTs switch the 12V, so a VFC needs to be created with a relay. Although I have no reason to believe that it would be a problem, I prefer that the sensor is not shorted when the car is running, so I used a second relay to isolate it.

[Joules]

Dave,

I'm interested in this and have a spare TTimer. Do you have any photos? or can you pass on a method and simlple circuit diagram??

Cheers,

Joules

[Dippy]

Tweaky - all my own work mate.

Joules - I'll put something together for you...

[Dippy]

1) Find the sensor. It has a green body and it can be located by looking at this diagram.



2) Disconnect the sensor and pull back the rubber shroud as far as possible. Cut the two wires so that you have enough length on both sides to do some soldering.

3) What you need to do is solder two long wires and these back together. You can try to splice into the wires without cutting them, but I tried and failed. Once you have tapped into this sensor you need to reconnect it and protect the wires. I used some heat-shrink tubing and some high-temp silicone rubber. Not pretty but it should resist the temps in the engine bay. I also used quite a few tie-wraps to keep the junction compact.

4) Run these two wires through a grommet and into the compartment where the battery and ECU live (you need to remove the long strip of 'rubber' first). Then run the wires over to the ECU box and into it as this is the best way to underneath the dash.

5) Now after the engine is switched off, if you short these two wires, the afterrun pump will stay on until you disconnect them or for 10 mins (according to ECU), whichever is shorter. It's worth testing this - I did.

6) So to get the turbo-timer to do this, you need a volt-free contact (don't apply power as this might damage the ECU). My Defi-HUD TT has an output which is normally connected to the ignition wire. Thus it gains its 12V from this wire to tell it the engine is on, and when the 12V is removed, it applies its own 12V instead, thus keeping the engine running. So if your TT is like mine then you need 2 relays like in this diagram.



Let me know if you need more info...

[DJG]

Nice one Dippy!

Thanks for the clear instructions.

[img]images/graemlins/beerchug.gif[/img]

David

[PhilT]

Wow, nice one Dippy. Top marks for quality content [img]images/graemlins/beerchug.gif[/img] .

[Joules]

Thanks for that Dave,

I'll have a go at the weekend [img]images/graemlins/thumb.gif[/img]

Joules

[johneroberts]

If we still had the stars system i would have given you 5 for that [img]images/graemlins/wink.gif[/img]
Oh well
Nice mate
Keep up the good work
jr

[Joules]

Yeah ...I was looking for the rank buttons??

How does the new system work??

Joules

[PhilT]

The new rating system is described here.

[Joules]

Dave, I have had a look at the method and was wondering if you could just drive the cirulation pump directly using the timed live from the T Timer rather than driving a relay.??

Joules

[Prawn]

Dave,
Will this work on pre 2000 year cars, I seem to remember that the water cooling was a later update on the turbo's?

[Dippy]

Dave, I have had a look at the method and was wondering if you could just drive the cirulation pump directly using the timed live from the T Timer rather than driving a relay.??

Joules

Maybe, but then you'd have to remove ECU control of it. So if there really was a problem where the coolant got too hot, then the ECU wouldn't run it for up to 10 minutes.

[Dippy]

Dave,
Will this work on pre 2000 year cars, I seem to remember that the water cooling was a later update on the turbo's?

Sorry, I can't be sure. However wouldn't that mean that pre-2000 cars would have had a different turbo without the water jacket?