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Intelligent Intercooler Water Spray - Part 4

Fitting the world's best DIY intercooler water spray control system.

by Julian Edgar

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When it came to installing the intercooler water spray system on my own Audi S4, I decided to take a slightly different approach to that implied in the previous articles of this series. Not because I think that the off-the-shelf kit has anything wrong with it, but because I like keeping my car looking quite standard...and that ruled out adding a new underbonnet water reservoir.

But I'd better start at the beginning.


The control module installation diagram looks like this:

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As you can see, the module needs to be connected to the two temp sensors, to one injector wire, to power and earth, and to the pump. On-board green LEDs show the status of each of the input connections, lighting up when the connections are correct (and when power is on!).

1. The Temp Sensors

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Two temp sensors are provided. If you buy the bare bones kit (to see in what forms the spray equipment is available, check the box at the end of this article), you'll get two thermistors that'll then need to be mounted. I started by shortening the wires to the thermistor, and then soldering each of these to a pair of wires running into a long cable.

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I then wrapped the joints with heat-shrink, crimped them to the terminal, and then covered the terminal in more heat shrink. This gave an easily mounted, sensitive thermistor. (Don't cover the thermistor itself in heat shrink; that would delay its response time).

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The Audi's air/air intercooler core is located in the left-hand front guard, and to access it I needed to temporarily remove the left-hand wheel guard liner. This done, the core was revealed, sitting almost parallel to the road.

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The intercooler temp sensor must be mounted with great care - it has to measure intercooler core temp on the back of the core, without the sensor being affected by radiator heat soak, heat from a switched-on headlight, etc. I narrowed the eye terminal with a pair of side-cutters and then slid the terminal down into the fins of the cooler itself. It was wedged in pretty securely, but to make sure that it stayed in place, I added a dob of adhesive.

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The ambient air temp sensor needs to be located so that it measures the temp of the outside air going into the intercooler - the temp of the day, if you like. In the Audi's case, this could be done fairly easily - the car uses a ducted intercooler and the sensor was placed at the beginning of this air intake. Again, when locating this sensor, beware of heat-soak from the engine, radiator, etc.

The two sensors were joined to a common 5-wire cable (multi-strand alarm cable bought from an electronics store) that was run back to the control module inside the cabin. The wires were wrapped in tape and care was taken that they wouldn't be subjected to chafing or vibration. (Five-wire cable was used to allow the duty cycle input to be part of the same loom.)

2. The Duty Cycle Input

Talking about the duty cycle input, to pick up this signal, one wire needs to be connected from the module to the switched side of an injector. But how do you work out which is the right injector wire to connect to? (You can pick any of the injectors - but which wire of the pair is the right one to use?) To make things easy, the module will in fact tell you. But since you'll need to have power to the module up and running before you can use this function, we'll come back to it later. At this stage, it's just important to include the extra duty cycle input wire in the loom that you're making. I made the injector wiring connection under the bonnet, which saved having to work out the ECU pin-outs.

3. Power and Earth

Power should be of the ignition-switched variety, and the earth - well, that just means any chassis point on the car.

4. Pump Relay

The relay wiring connections act just like an on/off switch, so connect the pump to the relay in the way shown in the diagram. The relay can handle 10 amps - so if you're using a monsta pump, check its current rating to make sure the current draw doesn't exceed this figure. If it does, you'll need to use another, separate power relay.

5. Powering-Up the System

With all the connections made but for the duty cycle input, apply power to the module. The Power On green LED should light, as should the Intercooler Temp OK and Ambient Temp OK LEDs. If the Power LED does not light up, check the power supply connections. If either of the temp LEDs stays dark it means that there is either a break or short circuit in these connections. Next, connect the duty cycle input wire to one wire of an injector. When this wire is connected correctly, the Duty Cycle OK LED will turn on and stay lit. If the LED is dark, or lights up only briefly then goes out, swap the wire to the other side of the injector. When the car is being driven along, all four green LEDs should be lit - four greens means that all the inputs are OK!

6. The Reservoir and Pump

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No matter which way I orientated the Holden/VDO water reservoir (described in Part 2) in the Audi's engine bay, it was a tight fit. Worse still, the only space available meant that it would have to be mounted directly above the ABS Hydraulic Control Unit (not great if the reservoir leaked) and also on very long brackets (not so good when the 2.5 litre container will have a mass of over 2.5kg when full). If the container absolutely had to go in here then it would... but was there another, better way?

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I liked the look of the standard windscreen washer container - at 4.4 litres it was big, it fitted the available space (funny that!), it contained an inbuilt strainer on the fill cap, and it also had an audible and visual indicator on the dashboard to show when its fluid got low. Could I add another pump to this reservoir - one just for the intercooler water spray?

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I pulled the standard reservoir out and discovered to my joy (yep, joy!) that it had been designed to take another pump - probably for the rear window washer of the wagon version of the Audi 100. Even better than that, after drilling just one hole, the Holden/VDO pump clicked straight into place - it was obviously the same pump that the reservoir had been designed to accommodate in the first place. Gotta be lucky sometimes I suppose....

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This meant that the pump could be seamlessly integrated under the bonnet, without any sign of its presence being visible.

7. The Spray Nozzle

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Given that the car uses a ducted intercooler (ie outside air is fed to the core through a specific passage), the obvious place for the spray was in this air intake duct. (But of course located well after the ambient air temp sensor!) I used a Spraying Systems TX-4 hollow cone spray, a filter/check valve (the latter very important in stopping the nozzle constantly dripping when it's mounted below reservoir level), and mounted the nozzle on a new bracket.

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While it's shown here without the lower grille in place, the spray nozzle assembly fitted behind the normal grille so again, it stayed invisible. The spray covers the core evenly with water, and because of the ducted intercooler construction, all of the sprayed water has to pass through the core - there's nowhere else for it to go.


What position you set the Fang Sensitivity and Temperature Sensitivity pots to will depend on a whole host of factors eg:

  • How big the intercooler is;
  • how much water you're spraying;
  • how big the water reservoir is and how often you want to re-fill it;
  • how big your injectors are;
  • what boost level is being used;
  • and how early boost comes on.

Rather than trying to work all of this out, it's a lot easier to simply set the pots on a trial-and-error basis. In the Audi, I set the Fang Sensitivity pot so that when a touch more than usual acceleration was being used, the Fang LED would light. So, normal acceleration away from the traffic lights didn't illuminate it, but pushing just a bit harder (like maybe you want to change lanes and you need to get in front of someone) would cause it to turn on.

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I set the Temp Sensitivity pot so that when the intercooler was warm to touch (about 10 degrees C above ambient) the Temp LED was lit up. These simple settings worked pretty well in practice - and of course can be easily changed if I decide that either factor comes into action a little early or a little late.

One point: if you live in a land of no speed limits, or if you tow a boat fast, make sure that at constant high speed both the Fang and Temp LEDs are not lit together (and so the pump LED is switched on). Of course, that will only happen when you're using a lot of throttle and the intercooler is hot (and so maybe it's much too small anyway), but in this situation you may have the spray running continuously, causing the reservoir to empty too quickly. When the controller is set correctly this shouldn't be a prob - eg with the Fang and Temp settings described as above, my Audi can be driven at a constant high speed without the Temp LED staying on, because the intercooler stays pretty cool with the extra airflow.

  Trips Earlier
(turn anticlockwise)
Trips Later
(turn clockwise)
Fang Factor
  • Will turn on at lower engine loads
  • Will turn on at higher engine loads
Temp Factor
  • Will turn on at lower intercooler temps
  • Will keep spray on longer after boost event is over
  • Will turn on at high intercooler temps
  • Will keep spray on shorter time after boost event is over

Remember - both the Fang and Temp LEDs need to be lit before the pump will switch on.

Note that the Temp and Fang adjustment pots are of the 25-turn type, giving excellent calibration sensitivity.


As outlined in Part 1 of this series, an intercooler water spray can only be correctly tested on the road. Road testing gives an accurate flow of cooling air, correctly creates heat-soak and other conditions, and gives real-life engine loads. Testing of the Intelligent Intercooler Spray was carried out on the Audi, which runs a standard 1 Bar of boost - a peak pressure that occurs at as low as 2000 rpm. To see what was going on, the actual intake air temperature on the Audi was continuously monitored with a fast-response K-Type thermocouple, read off on the AutoSpeed TempScreen (see "TempScreen: Part 1 - Installing the Intake Air Temp Probe" )dashboard LCD display.

Unfortunately, as the intercooler spray was developed during winter, full hot weather testing could not be carried out - summer is likely to show the system performing even better than in the test results covered here. However, on a 20 degree C day, full-load acceleration runs were undertaken through the gears from 0-160-0 km/h, followed by a U-turn and then an immediate repeat run to a higher speed: 0-180-0 km/h.

With the intercooler water spray working, the maximum intake air temp (recorded from the probe mounted directly after the intercooler) was 33 degrees C. When the water pump was disabled, this skyrocketed to a peak of 49 degrees C, with a temp of 42 degrees C held through most of the acceleration runs. That's a stunning decrease in intake air temp that occurs with the spray working.

Because the Intelligent Spray Control Module was left connected all of the time (just the pump circuit was disabled in 'no-spray' mode), looking at the module's Temp LED showed that when the water spray was working, the intercooler core came down in temp far faster than when the spray was not. Without the spray working, the core stayed hot for several minutes after the boost event was over, but when the spray had been working, the core was reduced to near-ambient temps after about 30 seconds.

In short, the spray system substantially reduced on-boost temps and also caused the intercooler to cool down far more quickly.

The 'intelligent' aspect of the control system also works very well. When the intercooler is cool (eg after a few kilometres of light-load cruise) the spray will not turn on even when you boot it - not until the core starts to heat up, anyway! On the other hand, when the core is hot, the spray will trip instantly when more throttle is used - and, if the core is not dropping quickly enough in temp - it will also keep the spray on even after the throttle is released. Driving along in cruise mode - followed by a quick burst of throttle - will not turn the spray on, but about 30 seconds later you will see the Temp LED come on as the heat-soak from that boost event gets the whole intercooler warm. Hit the throttle then and the spray triggers instantly.

In cool weather you can spend an hour driving around an urban area, squirting off every set of traffic lights - and the spray doesn't trigger once. The Fang Factor LED will light as you accelerate away - but the Temp LED's off because the intercooler is still cool. A few moments later, the Temp LED will light as the intercooler is warmed right through - but by that time you've throttled back and so the Fang LED's gone off. Driving in these sorts of conditions shows the enormous water savings possible - a boost pressure switch would have triggered the spray perhaps 20 times but the intelligent controller hasn't switched it on even once. That can cut by 80 per cent or more the number of times you need to refill the water tank.... And of course, if the intercooler doesn't drop enough in temp between those boost squirts, the spray will immediately trigger - and will then have a delayed on-time that's proportional to how hot the 'cooler core actually is.

The Fang learning behaviour can also be seen - drive the car hard for more than about 20 seconds and by looking at the Fang LED, you'll be able to see how early the Fang Mode trips into action when you again put your foot down.

If you're into the technology, it's all pretty cool watching those LEDs tell the story of what's happening. If you're not, that's fine - the system is working without any supervision anyway.


AFAIK, this is the first system in the world to monitor injector duty cycle as an input into an aftermarket control system. Add to that the ability to learn short-term driver behaviour, and measure actual intercooler and ambient temps, and it's a system that's damn good. Especially at this price...

Next week we will cover some of the other uses you can make of the module.

Intelligent Intercooler Water Spray - Part 1
Intelligent Intercooler Water Spray - Part 2
Intelligent Intercooler Water Spray - Part 3
Intelligent Intercooler Water Spray - Part 5

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The Intelligent Intercooler Water Spray Controller is available from the AutoSpeed Shop.

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