Member Since: 31 May 2015
Location: Perth
Posts: 2
TDV6 2.7 High fuel rail temp
Hi,
I've been chasing a problem on my 2010 Disco 4 for a few months now, my scan tool is throwing circuit high faults on the Fuel Rail Temp Sensor.
So I ran the data logger and when the engine is cold, it's reading 74C+ sometimes higher, depending on the ambient temp. When I unplug the fuel rail temp sensor the reading goes down to 50C.
The car is down on power and throwing some smoke out of the back under hard acceleration, according to the workshop manual when the fuel temp goes above 83C then the engine 'derates'. So it reduces the fuel pressure and I think I read somewhere that it changes the injector spray pattern. The result is performance loss.
When I unplug the fuel temp sensor and drive with it disconnected, it does throw a performance restricted error on the dash, but it feels no different to drive. i.e still low on power, but no worse than with the sensor plugged in.
According to the diagnosis steps the resistance between the power signal and ground should be above 100k Ohms, when I test it's reading 1K Ohm which according to the test procedure indicates that I have a ground to power short.
However, I have removed the wiring loom and inspected the wires and it all seems fine. When I put a multimeter on the pins at the PCM (ECU) I get zero resistance.
If I put a 270K Ohm resistor between the signal and ground wires, the temp on the data logger reads 67C. The workshop manual states that when the temp goes up, the resistance goes down.
When I load the wires with more resistance the temp goes up instead of down, so I'm at a loss what's happening there.
So, two questions :
1. Can anyone else verify that when they unplug their fuel temp sensor, can they check what the baseline temp is.
2. Does anyone have some test procedures so I can determine my PCM is faulty ? It's an expensive item to replace so I don't want to drop the cash on it without knowing for sure...
31st May 2015 6:43 am
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
BTTT to aid my memory!
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
The fuel temp sensor is a standard 5v NTC on the LP return line and yes, the resistance should go down as the temperature increases.
I cannot recall a default value for a detected short or open, but 50ËšC is a reasonable value to pick. It should also use a default value for rail pressure too as the two values are linked. The engine should go into derated mode when the rail temp hits 85ËšC to force more fuel flow around the fuel cooler. If the default set-points and remaining references become too divergent the engine will restrict performance further, prevent starting or even kill the engine when running.
I don't know how Australian vehicles are configured but I suspect you may also have the extra fan in the air intake ducting to the fuel cooler as we get on the armoured vehicles over here. This fan is not controlled by the ECM but has its own thermostat. I've had this clog with fine talcum-like sand/dust just as the locals got that murderous look in their eyes.
I'll grab some baseline figures for you later.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
Nobody brought me a 2.7L today, so no baseline readings for you.
The 3.0L engine fuel temp sensor is less than helpful in that it is buried in the V of the engine under a bunch of lines. I could only just reach it with my long backprobes. It is a lot easier to get to on the 2.7L engine.
For interest on the 3.0L it is located under the schrader valve at the back of the engine, grey connector with pink and green wires:
Click image to enlarge
Click image to enlarge
Key On Engine Off on IID:
Click image to enlarge
Idle on IID:
Click image to enlarge
The only odd thing I noticed is that when I faulted it to mega high resistance it was capped at minus 30ËšC.
If I see a 2.7L in the coming days I will take some values for you. To rule-out your wiring you could use backprobes and a jumper wires direct from the PCM to the sensor.
Hopefully a forum member with a 2.7L and a DMM will come to the rescue with some comparison figures.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 31 May 2015
Location: Perth
Posts: 2
Thanks Robbie,
Looks like Land Rover fixed the easy access to the fuel temp sensor on the 3.0L.
I removed the pin out of the PCM so the signal wire was completely disconnected and it defaulted to 50 C, so it looks like it is a default value I will run a jumper wire to rule it out 100%.
I've not found the fuel cooler, apparently it does have one... just a matter of digging around, the local off road environment over here is very fine talcum sand, so it might have been clogged by the previous owner
1st Jun 2015 2:19 am
lynalldiscovery
Member Since: 22 Dec 2009
Location: Maidstone
Posts: 7274
Ive seen the cooler on mine but for the life of me cant remember where! but pretty certain its a watercooled job so dirt clogging it wont really make any difference
1st Jun 2015 6:41 am
jimjpoole
Member Since: 08 Dec 2017
Location: Aberdeen
Posts: 1
Sorry to resurrect an old thread but I have exactly the same problem, if it is one.
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