Aux water pump and erratic idle when warm

[Rachel]

Hello,
What do you guys think? I have a new aux water pump fitted which comes on when the engine is cold, but any reasonable journey so the engine gets warm it doesn't come on...which obviously is when you need it most! Along with this I get very erratic idling when the engine is warm, but perfect when cold. Reliable sources inform me the fuel ECU controls the pump, which uses the engine temp. sensor, so it could be the earth to the ECU, the ECU its self or the engine temp. sensor.

I'd just like to hear your opinions on this, and or experiences. I'm leaning towards replacing the sensor as it's cheap and easy to do, and seeing if that makes any difference as I know they cheg up easily.

Thanks.

[doingitsideways]

Hmm...

Interesting one, this.

I always thought that the aux pump had it's own sensor?

Regarding your erratic idle, my best guess would be the ECU sensor, usually has a red two pin plug, sort of under the distributor facing forwards (side of the block).

Or, more to the point, the wiring to it. I went to change mine and the wires fell out of the plug. shoved them back in and my warm idle sorted right out

No signal from this sensor and the ECU presumes it's about -40c outside, fine from cold, rubbish when warm

Steve

Edit:
It does rather sound like your aux pump is working back to front, they are supposed to operate at anything above 40c (I think) once the engine is switched off.

Is the relay in back to front??

[jamescarruthers]

http://www.volvo-480-europe.org/forum/v ... 11&t=34099

Works on the temperature of the fuel injection system sensor. Click the link above and scroll down to the pics to read about the aux. water pump.

[Robou]

It's not that easy.
At first the aux. waterpump had it's own circuit.
Then the red Jetronic took over, using the general temparature sensor.
In April '92 an extra sensor and a replacement for the relay on position D was introduced. The Jetronic system was not changed, the sensor only supplied the relais at >105°C down to 100°C with 12V. I think this applies to Rachel's car from '95.
So the pump is connected to ground an a relay, which is governed by the Jetronic but finally gets it's 12V by the extra temperature sensor, overruling the Jetronic.
I would like to make an intelligent remark on the misbehaving of this all, but it is depending on the actual wiring and this could be far from original.

[jamescarruthers]

True, true. Forgot to state that my book is from late 80's. I didn't realise so much had changed with this system over the years. Pleased I know now!

[doingitsideways]

Aha... The Oracle has spoken

[Robou]

I hope somewhat clearer than a stoned priestess. Obviously clear enough to withhold further speculations.

[Rachel]

Got this sorted thanks to a big help from the only Oracle I know (you know who you are)

Causes where, bad connection to the engine temp sensor (it had no seal in it), bad engine temp sensor and corrosion inside the aux water pump. Also found the low speed fan wasn't cutting in due to some dodgy wiring....rewired that and now that cuts in as it should. 480 now runs very well at all temperatures.

Thanks to all for their input.