Member Since: 17 Apr 2012
Location: London
Posts: 425
"normal" values?
Where can I get a list of "normal" values for my car? Obviously, having diagnostic information is only part of the trick - one needs to be able to interpret it . So, for example, what should the engine coolant temperature be normally? Or the Air Conditioning pressure? How do I find the norms for the EGRs to work out if mine are performing correctly? And so on...is there a central source for these kinds of norms?
-simon
22nd Aug 2012 6:12 am
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
You will get a number of opinions on this and all will be valid. Some DTCs are relational and so have no specific limits (ie the car senses something really hot here and really cold over there, so something doesn't add up), hence no absolute values. Others have defined limits listed in the manual. Other fixed limits are just preset without the values listed.
Some DTCs are tied to fixed values due to the specific operation of a component. In the example you give (engine temperature) the coolant thermostat should start to open at 88degC and be fully open at 95degC. The thermostat itself is a dumb component and can be tested separately. Cooling effect is also part controlled by the ECM with a signal to the fan, so that has values too (and uses the ECT sensor). A dead or failing ECT sensor is checked (iaw workshop manual) by starting the engine cold and ensuring, by running for 20 min, that the temperature has increased by at least 10degC. Of course, if a cold engine already reads well above ambient temp then you know it is bust before you start. As the TDV6 is a very cool running engine it may never get fully warm when the conditions are cold (hence the FBH). If you know what other systems use a suspect value (eg aircon, in your ECT example) then it helps to validate the results. Multiple failures are rare and are usually linked to just one failure.
My point is that DTC codes and live data are only an aid and it is easy to get paranoid. The values have to be compared with other related systems and the conditions at the time. Clearly a coolant temp of 45degC is fine and dandy, but if it is displaying that with a stone cold engine then it is bust. A mismatch between this reading and another functioning sensor on the car may trigger another DTC flag on a system that is otherwise ok. Knowing what system is linked to what is a key part of diagnostics.
My suggestion is to 'learn' the vehicle when all is well as this may help using live data when fault finding.
As for your question on aircon pressures:
Quote:
To protect the system from extremes of pressure, the ATCM sets the A/C compressor to the minimum flow position if the pressure:
- Decreases to 1.9 ± 0.2 bar (27.5 ± 3 lbf/in2): the ATCM loads the A/C compressor again when the pressure increases to 2.8 ± 0.2 bar (40.5 ± 3 lbf/in2).
- Increases to 33 ± 1 bar (479 ± 14.5 lbf/in2): the ATCM loads the A/C compressor again when the pressure decreases to 23.5 ± 1 bar (341 ± 14.5 lbf/in2).
Of course, sometimes other diagnostic tools are just as effective:
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 17 Apr 2012
Location: London
Posts: 425
Ok, that's wonderful reasoning. The only problem is not having done the diags on a "known working" version of my car makes it hard to now work out what seems off
So specific questions I guess - for example, what is the highest you would expect the engine coolant temperature to rise? I've seen 130c - much higher than the boiling point of water, but I assume the coolant has a higher boiling point?
23rd Aug 2012 8:39 am
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
As I have covered elsewhere, your ECT sensor is faulty so don't trust the temp shown.
The coolant mix does raise the boiling point slightly (to around 107degC) at normal atmospheric pressure. A car cooling system is pressurised and it is this that significantly raises the boiling point. Most cars run at 15psi giving a typical coolant mix a boiling point of about 129degC. Take the cap off when hot and you are not just hit with the psi you are also hit with fluid that has just remembered its normal boiling point.
The coolant mix is actually a poor conductor of heat. Pure water is a much better coolant but comes with side-effects that you would not want on a normal car, but it is used on some race cars due its increased thermal capacity.Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 17 Apr 2012
Location: London
Posts: 425
I've had various theories - yours with the ECT sensor, another with the IAT sensor (which seems to read quite a bit higher than ambient), and more. That's why I'm trying to get a handle on what things *should* be showing!
23rd Aug 2012 12:07 pm
mrszymon
Member Since: 17 Apr 2012
Location: London
Posts: 425
Other things I don't understand:
- EGR throttle position (12.993%)
- EGR throttle command (4.997%)
- cooling fan speed - always 0%?
-simon
23rd Aug 2012 12:15 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
mrszymon wrote:
I've had various theories - yours with the ECT sensor, another with the IAT sensor (which seems to read quite a bit higher than ambient), and more.
Hopefully I gave you a little more than a theory. The only sensor used to provide the dash coolant temp display is the ECT - nowhere else. This gave us two choices:
a. The coolant really is that hot
b. The sensor is wrong
We ruled out 'a' as the temp was rising faster and hotter on your IID than is possible for a TDV6; indeed you said the temp was 95degC just after start. This left us with 'b' which is not an uncommon failure.
Regarding 'b' an over-reading sensor would trigger the ECM to issue a PWM signal to command the fan to max (the noise you heard perhaps) and shutdown the aircon - a symptom you said you had experienced. The ECM varies the PWM fan signal according to ECT, transmission oil temp, aircon switch, charge air temp and road speed from the ABS sensors (to allow for ram air effect).
The IAT is not connected to the coolant system or the aircon.
mrszymon wrote:
- EGR throttle position (12.993%)
- EGR throttle command (4.997%)
These values are fine and within spec.
I'm trying my best for you here.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 17 Apr 2012
Location: London
Posts: 425
Eeep, I didn't mean to sound disparaging! That's what comes from writing on an iPhone in the spare moments of a 300 mile journey, sorry
The suggestion of the other sensor was based on the fault codes mentioned in my other post. The thought was that the disparity of temp readings cause the engine to run lean, which in turn causes the engine to overheat when under heavy load. Hence my question of what is "normal". It it even possible for the temp to get that high? It seems it might be from what you've written. So that worried me.
Either way I have some more data from my drive today (Pisa to Chamonix).
1. Coolant temp at cold start was shown as 33c - ambient at that point was 30c.
2. Coolant temp very quickly rises to 90C or so, and hovers +/-5c of there while driving in the city
3. Coolant temp when the problem showed itself (uphill at speed) was 116c.
4. IAT after a short drive seems to show a difference of up to 20c higher than ambient temp
5. IAT when the problem manifested was only 3-4c higher than ambient
In addition, the route today was much more hilly (Alps!). I noticed that the car really seems down on power going uphill at speed. You hit the gas and it just doesn't go. There was a point where up a hill it was struggling to maintain 70mph...
Again I apologise if Ive come across negative, and appreciate your comments greatly
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. So, for example, what should the engine coolant temperature be normally? Or the Air Conditioning pressure? How do I find the norms for the EGRs to work out if mine are performing correctly? And so on...is there a central source for these kinds of norms?
