tiddy1 Posted July 16, 2004 Author Share Posted July 16, 2004 I tried switching the engine off with and without the fan running and the theory does seem to hold water, i.e it runs on when the fan is on . surely putting the fan on a relay would be a better solution that resistors and diodes so when the engine switches off the fan circuit is switched either open circuit or to ground? Simon Link to comment Share on other sites More sharing options...
Chris W Posted July 16, 2004 Share Posted July 16, 2004 Simon A relay seems like a great and simple solution and way back I too thought "Eureka". However, on thinking about it more closely, you will realise (as I did) that if the running fan keeps the supply lines high, then the relay won't actually drop out, even if the ignition switch is opened. The relay will still be receiving power from the fan's own voltage generation. From the viewpoint of the car's supply lines, the power is still ON for a few seconds. This is further compounded by the fact that a nominal 12v relay will close at around 9v but won't open typically until the voltage drops below maybe 4.5v. So the ECU will drop out (at ~6v) before the relay does. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
charlie_pank Posted July 16, 2004 Share Posted July 16, 2004 I don't have a heater, they're for girls (aparrently). Link to comment Share on other sites More sharing options...
Mr Locust Posted July 16, 2004 Share Posted July 16, 2004 .......warm girls 😬 Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
Jason Plato Posted July 16, 2004 Share Posted July 16, 2004 with sweaty feet 😳 Link to comment Share on other sites More sharing options...
Colin Mill Posted July 16, 2004 Share Posted July 16, 2004 While you could do it with a relay it would be a lot more work than fitting the diode. You would have to remove all the load from the ignition switch and use it to switch the relay only. The relay would have to be a two pole type so that you could switch the ECU with one pole and all electric motors off the other. That way the relay would drop out because you had open-circuited the coil drive on turning off the ignition switch. The two poles would ensure that the current from the fan(s) would not get to the ECU. However it would be a hell of a lot of trouble to go to. The diode way is a two minute job with a soldering iron or some Lucar connectors. Alternatively just leave the headlights on all the time Volvo style - at least that will reduce the run-on time. Colin Link to comment Share on other sites More sharing options...
csedgwick Posted July 16, 2004 Share Posted July 16, 2004 Try leaving the heated screen on when you turn off the ignition with the fan running. I'd imagine the current required by the element would quickly drag down the coolant fan. Link to comment Share on other sites More sharing options...
Chris W Posted July 16, 2004 Share Posted July 16, 2004 Colin Not sure even that would work because there would still be a path from the fans to the relay coil unless one ran separate live feeds from the battery to each of the the 2 poles .....and the relay would also become a very critical single-point-of failure. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Colin Mill Posted July 16, 2004 Share Posted July 16, 2004 Hi Chris Yes, you would need seperate feeds to the two poles of the switch and have the relay coil as the only load connected to the ignition switch. I agree, the relay would be a rather critical component and I don't fancy it at all. These days semiconductors are used a lot in mundane tasks in cars from switching interior lights upwards so the diode solution is not that off the wall. Come the 42volt revolution and CANBus there will be almost nothing on a car that is not semiconductor switched. Nice simple wiring looms but a software nightmare! Colin Link to comment Share on other sites More sharing options...
Chris W Posted July 16, 2004 Share Posted July 16, 2004 Hi Colin I agree. I used to have a Jeep Grand Cherokee 4x4 which had an Ethernet Lan instead of hard wiring. So, for example, when one pushed an electric window switch, the switch didn't connect to the window motor but instead sent a command, via the Lan, to a CPU which processed the command and instructed the motor to operate. Imagine trying to fault-find on that! Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
CHRIS CLARK Posted July 16, 2004 Share Posted July 16, 2004 Had this with my 'K' series with the Emerald ECU whether the rad fan was running or not! Pretty scary to be able to pull up at home, turn the key "off" and undo the harnesses and almost be getting out of the car before the engine died. Karl @ Emerald checked the ECU which showed it was being held 'on' with only about 3.2 volts across it. He inserted another resistor which meant the ECU 'died' when voltage decayed to about 6 volts. Problem solved even with the rad fan running. Instant switch off!!! Link to comment Share on other sites More sharing options...
raw Posted February 6, 2005 Share Posted February 6, 2005 I sorted this problem by ensuring that both supply lines to the Emerald (Pins 11 & 28) are both fed from the ignition switch. Now when I switch the ignition off with the key (car has a starter button), the engine dies instantly. Before I did this mod, the ECU stayed powered up, along with the lambda sensor heater, quickly draining the battery. Link to comment Share on other sites More sharing options...
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