In a bind with a cooling system

[RustyNuts]

Evening all!

 

Ok so the safrane has a dual speed fan unit and as it's a big volvo 2.4 engine (B5254S) it needs that extra hi speed for when it gets waaaaay too hot.

 

Now the ECU packed up a while back after an ignition coil failure and as a consequence, no longer grounds the two relays in order to control the hi / lo modes.

 

So.. armed with an arduino nano microprocessor, a dual relay unit, some resistors and verroboard, I put together a crude but functional cooling computer that reads the voltage of the temperature sensor and activates the cooling either in hi or lo mode in order to cool the system down. Granted it's shutting the stable door after the horse has bolted (head gasket is shot) but with a replacement engine in the garage i'm hopeful that it will stop that being burnt to a crisp.

 

Now I have a problem. I've used a couple of spare connectors from an old loom to connect between the temp sensor and loom but allowing me to attach another wire inbetween and pass that voltage down to the unit i've made. The problem however is that the voltage on it is hovering around the 5v mark, doesn't change much and when it does, it's mV and seems to sway drastically from one reading to the next (every 0.5 seconds). It can go from 5.03 to 5.17 within one reading... and then back down again. Thats not a big problem.. I could fill an array with 10 reads and use that to work out an average ... but it's upsetting the dashboard and causing me some blinky lights everywhere. Oh yes.. it also stops the temp gauge on the dash working which obviously makes it hard to program in the right voltages using the gauge to help me get a rough idea.

 

So.. I really need to get this car through an MOT just to keep me motivated and having watched a complete wreck on car SOS be made into a minter, I'm convinced there is still life in the old dog yet.. as long as I can get this blasted cooling sorted.

 

So I was thinking that perhaps the ECU is still expecting to read a small current through the existing wiring and if thats the case, me having disconnected it and wired them up through some relays won't be helping. So what would happen if i simply reconnected that wire but still controlled it being grounded from my unit? - The ECU isn't doing it anymore for whatever reason, is there a risk of me causing it further damage if i ground the whole wire beyond the ECUs control?

 

Does anyone know of a ECU specialist who would have half a clue where to start with this or at least give me some advice?

 

Many thanks,

 

Rusty

[AMC Rebel]

I am mega impressed with your arduino zen.

 

One of the geezers over on the Rover 75 forum did something similar by effectively using his own temp sensor strapped to the top hose (I think it was).  If you did this you could effectively isolate your electronics from the rest of the car.  His was a lot less sophisticated mind you.

[AMC Rebel]

Thinking about it - could you just wire up the fan to be on full for the duration of the MOT and reconnect the old wiring?

[Asimo]

Need to know what sort of temperature sensor it is: temperature dependant resistor, thermocouple, temperature dependant current source or something perversely Renault.

Engine electronics have to work in a very (electrically) noisey environment so earthing and decoupling is very important, as, you have already mentioned, is software filtering of signals.

I would keep it simple and just use a thermostatic switch and a relay or two. High speed is probably only needed when aircon is on.

[twosmoke300]

Could ecu testing / actronics or bba reman not repair the old ecu for much less hassle ?

[RustyNuts]

Hi lads,

 

I am mega impressed with your arduino zen.

Thanks .. but i'm no genius... lol

 

One of the geezers over on the Rover 75 forum did something similar by effectively using his own temp sensor strapped to the top hose (I think it was).  If you did this you could effectively isolate your electronics from the rest of the car.  His was a lot less sophisticated mind you.

 

I have a spare top hose and did think about drilling a hole into it to fit a waterproof temp probe (removing it first, feeding it through from the inside and thus the large part blocking the hole) however I decided this would be a bit of a bodge and decided to read from the main engine temp probe instead. Trouble is that it's looking to be putting out an analogue signal which is slightly unreliable unless I average it out.

 

Thinking about it - could you just wire up the fan to be on full for the duration of the MOT and reconnect the old wiring?

I did think about that but hi speed mode uses a lot of juice and the battery isn't in great condition.. and with money lacking and the batteries for this car costing mega bucks...

 

Besides... I rather like the thought of my own automatic fan unit lol. It's just a pain that it's upset the dashboard.

 

 

Need to know what sort of temperature sensor it is: temperature dependant resistor, thermocouple, temperature dependant current source or something perversely Renault.

Engine electronics have to work in a very (electrically) noisey environment so earthing and decoupling is very important, as, you have already mentioned, is software filtering of signals.

No idea what type of sensor it is, I will have to dig out an old spare one and get back to you on that... but I don't recall there being any markings. I will make enquiries either way.

 

I would keep it simple and just use a thermostatic switch and a relay or two. High speed is probably only needed when aircon is on.

I did think about that but with it being dual speed, I decided against it. The hi speed is frequently used on a hot day without the aircon being activated hence I do really need it working. It's not the biggest engine but at 2.4L it does generate a lot of heat.

[scaryoldcortina]

I wouldn't have thought that just splicing a 5v signal wire into high Z input like an arduino would bother the original signal much at all, maybe there is something else going on?

[AMC Rebel]

Hi lads,

 

 

I have a spare top hose and did think about drilling a hole into it to fit a waterproof temp probe (removing it first, feeding it through from the inside and thus the large part blocking the hole) however I decided this would be a bit of a bodge and decided to read from the main engine temp probe instead. Trouble is that it's looking to be putting out an analogue signal which is slightly unreliable unless I average it out.

 

The guy that did it on the rover just cable tied the temp sensor to the hose - it wasn't a screw-in automotive one he used, but it was accurate enough from contact with the outside of the hose - it's more about change of temp than absolutely accurate values. 

 

I know what you mean about two speed fans - I have just replaced the big resistor on the Puma so I've got slow speed back.  It works fine without it, but then high speed cycles on and off a lot (esp with aircon on) and it's not as effective as having the system working as intended.  As an aside, both my MG ZT and Puma systems are 2 speed - but both put the slow speed on at all times when aircon is selected.

[RustyNuts]

I wouldn't have thought that just splicing a 5v signal wire into high Z input like an arduino would bother the original signal much at all, maybe there is something else going on?

I know.. it's weird!

 

The ECU definitely didn't like the loom to the fans being unplugged though... and now i have the two ground wires for the two speeds going through relays i wonder if it is perhaps looking for a small current there just to establish the circuit is intact? - So that being the case, i wonder what restoring this would do if i still kept a switchable ground wire in there.. would i then blow the ecu to bits grounding those wires while still connected to the ecu?

 

It's a nightmare... it really is.