Engine stalling

[blackflash]

I have posted before (I think!) about my car having gone into Restricted mode on a couple of occasions which had the following in common:
- cold weather (not a scientifically precise term, I know)
- engine not fully warmed up
- acceleration/kick down to overtake OR pull out into line of traffic sharp-ish in Sports mode having been flashed
- followed by braking...
So I assumed the problem was over-supply of fuel (flooding) of some sort.

At last service a few months ago David Marks investigated and found nothing untoward. I tried to recreate the situation (without traffic of course) in the summer months but to no avail. I have generally avoided accelerating other than v gently until thoroughly warmed up which probably makes sense anyway but sometimes I'm heading for a train to London and there's that tractor in the way...

This morning the car caught me by surprise. 11 degrees is not exactly cold weather; no acceleration (and certainly no kick-down); went round a bend which needed gentle braking and... no response on throttle out of the corner. Pulled into convenient layby which is about where the car has struggled before... no Red light, no Restricted mode but as I gently pulled into the layby the panel showed "Engine Stalled". I turned the key and it started first time and the rest of the journey was fine (and I caught my train). Not sure if this is related to/a different version of my earlier problems.

In David, I know I have one of the best around and it makes me glad I live near Nottingham. But i'd appreciate any suggestions or similar experiences which would give us a clue where to start looking. This is so sporadic and it's frustratingly difficult to recreate the problem on demand for diagnosis...

Thanks in anticipation,

Nigel

[dhammond]

It may be the engine coolant temperature sensor (the one that feeds to the ECU, not the one that goes to the temperature gauge). If this has failed into a lower resistance mode the engine will think that it is warmer than it really is and not use the correct fuel mapping. This type of fault can only be found when the engine is cold as once the engine is warm the sensor can be giving the correct reading.

Unfortunately I cannot find any resistance vs temperature tables for the sensor used in the XJ8 which would allow you to use a multimeter to fault find. Without a resistance table, you need a fault code reader that can display live data to see what the engine thinks the temperature is when it is cold. Other options are:-

a) An engine data recorder such as a Launch CRecorder (around £45) to record sensor data over a full drive cycle and then download to a PC later for monitoring.

b) A in car display such as DashDaq (around £370) or Autel MaxiTrip (around £90) to display the information whilst you are driving.

These all take their information from the cars OBDII socket (diagnostic port).

c) Buy a engine coolant temperature sensor (around £7) and measure the resistance on that using a multimeter and compare it against the resistance of the sensor in the car.

If you do not have access to diagnostic equipment then the vehicle needs to be left overnight at a car maintenance garage (when you know it will be cold the next day) so that they can connect up their diagnostics equipment when the whole car is cold and see what faults are flagged.

Regards,

David

[blackflash]

That's really helpful David; many thanks for such a quick and full response. I will consider further with a view to discussing with David Marks how we might pursue this line of enquiry.

[u102768]

Unfortunately I cannot find any resistance vs temperature tables for the sensor used in the XJ8 which would allow you to use a multimeter to fault find. Without a resistance table, you need a fault code reader that can display live data to see what the engine thinks the temperature is when it is cold.

If you mean the engine coolant temperature sensor that feeds the engine control module, then the data is:

Temp - Resistance
deg C - K ohm

-20 = 15.04
0 = 5.74
20 = 2.45
40 = 1.15
60 = 0.584
80 = 0.32
100 = 0.184