diesel heat plugs switch
 

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 :eek:

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 :
http://www.groar.org/EcoModder/Megan...under_Hood.jpg
Here the black cables are the kill switch and the blue ones are for the heat plug switch :
http://www.groar.org/EcoModder/Megan...dUpDisplay.jpg
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 :confused:

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 :

1. put in neutral
2. switch off the heat plugs switch
3. switch off the kill switch
4. switch on the kill switch (1)

To restart the engine :

1. switch on the heat plugs switch
2. 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 :eek:

Have fun,

Denis.

Do the noises go away if you switch it back on after restarting the engine ?

And do the heating plugs fire up after you've started with the switch off , then flick the switch on again ?

What kind of noise -- does it sound like it is harder to start (and any additional black smoke from the exhaust)? Is it like if you don't wait for the plugs to warm up and you start early?

Maybe the ECU is concerned about the turbo -- is there an increase in consumption with the switch on during normal operation (or the ability to monitor boost in this situation)?

Just brainstorming -- but great find with the plugs and working the problem!

:thumbup:

-RH77

The noise appears around 1 second after I switch off and disappears around 1 second after I switch on. This is why I'm thinking that the ECU detects something strange and switches to a degraded mode.

When I switch on, engine on or killed, the heat plugs are heating up (deduction from the sudden voltage decrease).

I can't say if there is an increase in consumption. If I had an iFCD (*) I don't think I would be playing with the engine :o

I have no idea what happens exactly. The noise is the same when I try to start the engine with the cable to the needle lift sensor disconnected. This may be another indication that the ECU falls into a degraded mode.

The noise is louder when the engine is pulling the car, than when the engine is idle.

The noise is present whatever the engine temperature. It may be louder when the engine is cold, but I can't say for sure as I switched off with cold engine while idling. Now I try to switch off only when the engine is idle, so the described method...

I'll look at the pipe tomorrow to see if some (strange) fume appears when switch is off.

Thanks,

Denis.

(*) the signal from the needle lift sensor may be my next game...

Maybe the fuse you tapped into controls more than just the glow plugs? Have you been able to get an electrical wiring diagram of your car/engine? Have you asked around at a Renault forum about how the glow plug subsystem works??

My advice is to find your glow plug relay and check which wires do what: Usually you will have a pair of wires which activate the relay, plus one thick wire going in with the supply voltage for the plugs and either 4 or 1 (in older models) going out to the plugs. Some cars (PSA diesels, for example) also have an 8th 'control' wire which goes back to the ECU to let it know whether the relay activated when it was supposed to. You can tap into either the wire which activates the relay (may cause the ECU to throw a code) or the thick supply (switch/relay must handle higher power).

You could automate your set-up so that the glow plugs are deactivated whenever coolant temperature is above 60°C, for example. This can be done with a simple circuit of the type found in household thermostats for controlling central heating.