After my
diesel FAS kill switch, here is my new project : diesel heat plugs switch.
The reason is simple : at each FAS and each bump start, the heat plugs are heating during 8 seconds. The 4 heat plugs are pulling 15A each. During my daily commute the heat plugs are on at least during a third of the 40 minutes, ie
4 * 15A * 12V * 40/60 * 1/3 = 160Wh of electricity
As the alternator is 50% efficient and the diesel engine is 33% efficient, these 160Wh of electricity are generated by
160Wh / 50% / 33% = 960Wh of diesel
As diesel is 32.19 MJ/L = 8.94 kWh/L, these 160Wh of electricity are using
960Wh / 8.94kWh/L = 0.10L of diesel.
On my 40km daily commute, this is
0.10 / 0.4 = 0.25L/100, ie
8.2% of my last tank at 3.021L/100
The goal of this mod is to prevent so much sucking from the heat plugs. As for the kill switch, I tried to remove several fuses and found one that will make no voltage drop when the key is put on II :
Here the black cables are the kill switch and the blue ones are for the heat plug switch :
The left switch is the new one.
Whatever the engine state, if the key is on II then the heat plugs will heat up 8s as soon as I switch on the new switch. If I put the key on II with the new switch off then the heat plugs doesn't heat up.
The bad news :
- the engine makes a strange noise when it's started with the new switch turned off
- it makes the same strange noise when the new switch is turned off while the engine is on
In both cases, the engine is then missing a lot of power.
After lot of readings on Internet, it seams that a lot of diesel engines are using a degraded mode when they detect something wrong. Here it seams the ECU is detecting that some signal is missing
This means that I can't simply switch off the new switch when I think that the engine is hot
Nevertheless I tried to apply this method during a short errand :
To FAS :
- put in neutral
- switch off the heat plugs switch
- switch off the kill switch
- switch on the kill switch (1)
To restart the engine :
- switch on the heat plugs switch
- bump start
With this method the heat plugs will switch on only between step 1 & 2 of engine restart and during 8s after bump start. If I coordinate correctly, this means the heat plugs will heat up only during 9 seconds instead of 16, ie more than 40% energy saved and more than 0.10L/100.
I looked at the voltmeter during this test. It never went under 13V when I was correctly applying this method
Without the new switch, the voltage is quickly dropping down to low 12.xV as soon as I FAS. At bump start, the voltage was slowly increasing to high 13.xV while the heat plugs are heating, then to 14.2V when the heat plugs are switched off by the ECU 8s later.
Now at FASing the voltage is slowly going down to low 13.xV and at bump start it's quickly going up to 13.9V-14.1V, then to 14.3V as soon as the heat plugs are switched off by the ECU 8s later.
(1) I switch on the kill switch a short period after it's switched off because I don't want the anti-thief system to switch on... To deactivate the anti-thief system I would have to :
- remove the key
- lock the doors
- unlock the doors
Then I would have to put back the key and turn it to II... and all that while the car would be FASing and if I have to turn the steering wheel it will be locked
Have fun,
Denis.