Member Since: 04 Feb 2015
Location: Gloucester
Posts: 352
Science experiment
anybody up north or in colder climates want to try the resistor trick and see if the discovery 3/4 will start in temps lower than -4.
Being a southern softy that's as cold as it gets here.
6th Dec 2022 11:29 am
Flapper
Member Since: 04 Feb 2015
Location: Gloucester
Posts: 352
bump
bump
6th Dec 2022 12:49 pm
classic kev
Member Since: 12 Feb 2021
Location: Mold
Posts: 204
Stuck glow plugs would be a bit of a problem. £5k from Land Rover to replace the glow plugs seems more than just a tad steep to me. Anyway, a D3 will start without modification in low temperatures; when I bought mine it was in an unusually cold snap and sub-zero temperatures. It took a bit of cranking but it would start but was rather smokey with a rough idle.
With 5 of 6 glow plugs replaced this year it now starts easily and quickly and a working FBH helps it warm up.
7th Dec 2022 8:00 am
Unbeliever
Member Since: 28 Aug 2022
Location: South Yorkshire
Posts: 27
Been having the same issues as you Flapper since the temp dropped last week.
Once the temp gauge reaches 0 deg. she just cranks and cranks but wont fire, without pouring a kettle full of boiling water on the ECT.
Have used the same trick each day over the last week when external temp was supposedly -4 deg C (according to the information screen).
Well, having consulted the Service Manual, the Engine Sensor section lists the ECT (Engine Coolant Temperature) sensor description as follows:
"The engine coolant temperature sensor is located in the top hose at the coolant manifold junction. The ECT sensor
provides the ECM and the instrument cluster with engine coolant temperature status.
The ECM uses the temperature information for the following functions:
Fuelling calculations
Limit engine operation if engine coolant temperature becomes too high
Cooling fan operation
Glow plug activation time.
The instrument cluster uses the temperature information for temperature gauge operation. The engine coolant
temperature signal is also transmitted on the CAN bus by the instrument cluster for use by other systems.
The ECM ECT sensor circuit consists of an internal voltage divider circuit which incorporates an NTC thermistor. As the
coolant temperature rises the resistance through the sensor decreases and vice versa. The output from the sensor is the
change in voltage as the thermistor allows more current to pass to earth relative to the temperature of the coolant.
The ECM compares the signal voltage to stored values and adjusts fuel delivery to ensure optimum driveability at all
times. The engine will require more fuel when it is cold to overcome fuel condensing on the cold metal surfaces inside the
combustion chamber. To achieve a richer air/fuel ratio, the ECM extends the injector opening time. As the engine warms
up the air/fuel ratio is leaned off.
The input to the sensor is a 5V reference voltage supplied from the voltage divider circuit within the ECM. The ground
from the sensor is also connected to the ECM which measures the returned current and calculates a resistance figure for
the sensor which relates to the coolant temperature.
The following table shows engine coolant temperature values and the corresponding sensor resistance and voltage
values."
Coolant Temperature Sensor Response
If the ECT sensor fails, the following symptoms may be observed:
Difficult cold start.
Difficult hot start.
Engine performance compromised.
Temperature gauge inoperative or inaccurate reading.
In the event of ECT sensor signal failure, the ECM applies a default value of 80°Celsius (176°F) coolant temperature for
fuelling purposes. The ECM will also permanently operate the cooling fan at all times when the ignition is switched on, to protect the engine from overheating.
If I'm understanding this correctly, a normal cold engine starting temp. of 15 deg. C would have a sensor resistance of ~ 45Kohm.
Only got it fitted this afternoon and it was -1 deg. C when I'd finished. I set it to 10K ohm (~50 deg. C) and I did get it fired up after about 20 seconds of cranking I also had to give it some right foot and keep the starter cranking whilst she started. Does this sound right?
Am 100% going to get the Glow Plugs done after Xmas but I'm hoping this will get me through 'til then.MY06 D3 SE 2.7 V6
MY15 FL2 SE 2.2 I4
11th Dec 2022 11:18 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10673
Not sure why your straying away from proven values. I think 2k and 5k are proven to work.
Then return to the sensor once running.
11th Dec 2022 11:35 pm
Flapper
Member Since: 04 Feb 2015
Location: Gloucester
Posts: 352
Spot on Pete that's what I was going to say.
You want it to think it's just above freezing about a quarter or less on the temp gauge.
12th Dec 2022 7:23 am
Flapper
Member Since: 04 Feb 2015
Location: Gloucester
Posts: 352
Also check you starter speed, mine was very slow 100 ish rpm this is way to slow to start the car in the cold.
Check out https://www.disco3.co.uk/forum/fast-d3-turn-200919.html
i had mine changed (i think its a disco 4 as your have to change a bracket) and now it starts at about
280 rpm. the difference is the motor fires up instantly no more churning over it just starts.
The problem is you dont notice it slowing down
I only noticed how slow it was, when i was parked next to my brother in laws disco4
so far i have used the magic button twice in December -1 and -2.
If you have a variable resistor turn it down to 5000 ohms or less you just want the sensor to think its about 2 degrees C not think its been belting down the motorway and it needs to do a hot start.
f
12th Dec 2022 10:42 am
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10673
Think about it.
A 5k resistor means it’s around 70C
And boiling water means it’s hot.
Ecu must inject more fuel when it’s hot to make it start ok without Glowplugs
12th Dec 2022 10:48 am
epninety
Member Since: 12 Oct 2012
Location: Hampshire
Posts: 329
Had to try the boiling water trick this morning, for the first time after 10 years of D3 ownership. Happy to report it works exactly as stated
Thinking about why it works though, I wonder if it's not the temperature reading itself that's important, but the effect it has on the engime trim. It seems quite 'digital' to me, in that my 220k D3 starts easily at 0C, but at -3C shows no hint of starting at all. So I wonder if what really happens is that some calculated value in the ECU is adjusted by the temperature reading, and it's just reaching an 'error' value and dropping back to a safe default (which isn't enough to allow the engine to start when cold).
Doesn't really matter, just thinking out loud.
12th Dec 2022 11:46 am
Flapper
Member Since: 04 Feb 2015
Location: Gloucester
Posts: 352
Pete
Have you got the same table as above as im sure you posted one on here which was the other way round
f
12th Dec 2022 11:52 am
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10673
That table is the same as I remember it.
12th Dec 2022 4:35 pm
munst
Member Since: 16 Sep 2020
Location: GLOS
Posts: 155
I remember reading in another thread that the same engine in the Peugeots start much better even without glowplugs so the assumption was that it is down to the engine management map that LR uses.
12th Dec 2022 8:38 pm
Unbeliever
Member Since: 28 Aug 2022
Location: South Yorkshire
Posts: 27
Pete,
Quote:
Not sure why your straying away from proven values. I think 2k and 5k are proven to work.
Then return to the sensor once running.
I was going to go with a 2K or a 5K, but according to LR's own data (in that table) that would tell the engine that the coolant was between 75 - 100 deg. C, and somehow that just doesn't seem right for a cold engine and I was worried about doing more harm than good.
Flapper,
Quote:
Spot on Pete that's what I was going to say.
You want it to think it's just above freezing about a quarter or less on the temp gauge.
Thats what I was trying to achieve, according to the chart 50K ohm = 15 deg. C (ish)
Maybe thats way off and you do need to fool it into thinking its near boiling?
As you said earlier in the thread, a variable pot ought to make it easier to fine tune...I think I'm going to have a few more days to try if the weather carries on like this.
As for the cranking, when it's warm it fires up within half to one second. It's just in the sub-zero that it's been struggling. I've got an Autel AP200 diag tool and hopefully will be able to check the crank speed/fuel pressure on that....failing that I might ask Mrs Santa if an IID is in her price range MY06 D3 SE 2.7 V6
MY15 FL2 SE 2.2 I4
12th Dec 2022 11:55 pm
Flapper
Member Since: 04 Feb 2015
Location: Gloucester
Posts: 352
If i sit in the drivers seat put the 5k resistor across the sensor my temp gauge sits at about a third so its above the blue bit but not as far at halfway.
Then i turn the key and it starts just like its 10 degrees outside. no endless churning over it just starts.
This may be to do with the new starter motor that spins my engine over at 280rpm or the new fuel filter or i have been very lucky and picked the resistance that just works.
Pete K helped at the beginning as i cant find the original post when the eureka moment happen and it started.
I would like to have new glow plugs but so far 2 independent LR specialist have both had a go and cant do them. Land rover can do them but want to remove the body then the heads and that's 5k.
Well the weather so far has tested it to -3 and it starts i'm a happy chappy.
f
14th Dec 2022 3:24 pm
Flapper
Member Since: 04 Feb 2015
Location: Gloucester
Posts: 352
Disco's normal temp is about 90 degree c so 70 is about a third which is about 5k on your table.
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I also had to give it some right foot and keep the starter cranking whilst she started. Does this sound right?
