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This is quite a complicated HOW TO so i though id'd try and explain how it all works so sorry if i go on a bit
First of all the problem...
Vauxhall in their divine wisdom designed a pre-heating system for thier diesels, that works only when the temp is low enough..
Some say 6'c, some say 5'c, but in my experience the glow plugs system is not activated until engine temp is below 4'c..
This is fine for nice new cars, but for a diesel engine with loads of miles on it like mine, it can some times be better if it has some extra help to start in colder weather.
I must add that when the glow plugs come on on there own there no problem at all, and starts within 2 seconds....
So basicly in the summer its fine, in winter its hard to start, but when its very cold in the winter ie- under 3'c or 4 'c the glow plugs will come on all on their own and all is great...
Other starting problems can include air getting into the diesel system via, leak off pipe, valve seals, or some other seal or leak.. Which is a different matter alltogether.
Now..... the ecu takes a reading from the CTS (coolant temp sensor) to see how cold the engine is.. The CTS is basicly a Variable resistor controlled by temperature.
Resistance is measured in "Ohms" so the ecu measures the amount of "Ohms" being let through by the resistor.
The Higher the the engine temp the LOWER the Ohms
The Lower the engine temp the higher the Ohms....
If you disconnect the CTS wires there is maximum resistance (not even connected together) thus the ECU would think it -17'c or something
So at 10'c the resistance could be 2000 ohms
at 20 'c the resistance could be 138 ohms
AND the figure we need is for -1'c.........6000 ohms
What your trying to achieve is to trick the ECU into thinking its very cold and make the glow plugs come on.
The great thing about this little modification is that it only changes the normall way of wiring when you press the button, at ALL other times its exactly as original.
What you need..
A 5 pin relay
A 6k Resistor (6000 Ohms) Or any near 6000 should be ok
wiring
A momentary Switch
Some spade connectors, male and female, and you need to make the male ones smaller..
Tools, Pliers or crimpers, e.t.c.
These are basic diagrams of what your trying to achieve...
From this
To this
So as you can see what were doing, is for a few seconds, while the switch is pressed, the flow of Ohms to get sent through the resistor on its way back to the ECU
You cant have it permantly going through the resistor otherwise the ECU will always thinks it cold...no good for mpg
or your engine
And cant just unplug the CTS as the ECU management light comes on...
ok here go's....................
OK you need to stick a switch in somewhere...i always like to keep things looking nice and normal so i put a rear window heater switch in an empty space and wired a live to that (and the lights and the on light too) so it lights up with the rest....
Alltough any MOMENTARY switch will do...
Its up to you if you want your switch permant; live, or switched live, , Mine is by a switched live at position number 2
Wire the switch in and run the switch live to the relay... I put my relay in the engine bay... Near the air filter...
once youve mounted your relay and earthed it, , the wiring connections are like this...
1 to live from switch
1 to earth
1 output to ECU
1 input from CTS
1 output to resistor and then onto ECU
The way it works is that its always connected as normal when button is not pressed, but when button is pressed it changes it go through a 6 K Resistor too
The relay i used was marked up like this, and wired like this..
Once the relays in and earth is connected and the wire to the switch..
You need to connect the input from the CTS and the return Wire for the ECU, not forgetting of course to wire in the 6k resistor into the correct output as shown above..
Ok now to the CTS wiring
Take off the ecotec cover ,, 3 torx screws and its off
The CTS and its connector and wiring is here
Unplug it ! its the one with the 2 wires coming out, (not the 1 Wire one ! thats for the temp gauge on dash). It comes out by pushing a clip in and pulling it up.
And check out the connections you need to make into both the plugs
Once thats out you can see the four connections.
Its the Blue Wire that you need to get at,,,,the brown one just go's straight back into the CTS.
NOTE: you could just cut the blue wire and tap into it that way but i prefer to make it totally reversable, so i used connectors.
The ones in the CTS need small female, and the ones going into the plug that go's back to the ECU needs to be filed, or ground down male spade connectors..
So once you've figured what you need to do and you have what you need...
Run your 2 wires from the relay to the CTS, When crossing over the radiator and its hoses you may want put the wires in some time of protection like i have (shown below)
Once its all connected try it out !
When warm the glow plugs shouldnt come on..
So without turning the key hold the button in then turn the key to position 2, the glow plug warning light will come on, , wait a few seconds then start the car...
The glow plugs will actually stay on for as long as you hold the button in...upto i think 17 seconds....Let go of the button and the ECU tells the pre-heat system to turn off..
Now try it without the button pressed and there should be no glow plug lights..
Thats whats clever here , ,, your not actually switching the glow plugs on, your just telling the ecu its cold enogh for them !
Once your sure its all ok, you need to work out when to use it !
Mostly i use mine first thing in the moring and after a full day of not being started !
Even when the car is idling and you press the button the revs rise a bit as yje ECU thinks its cold again ...... Could use it as a nice little boost !
Have fun
Mike
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