immobiliser mischief
 

I am having exacly the same problem, doen't start randomly. Today started fine, travelled 50 miles , restarted 3 times, travelled 50 miles, stopped for lunch, refused to start.
I shall be trying again after sending this.
Is it possible to disengage the immobiliser?

Immobiliser, non starting
 

After a 2 hour wait the engine has started, any views

As mentioned before Cam Sensor most likely the culprit when there is a hot start problem.

Quick test if car doesnt start when hot take off the cam sensor, place in fridge for 10 mins, and refit. If the car then starts you need a new sensor.

How about the under bonnet diesel pump.........??? Mine did this the other day, gentle "adjustment " with a hammer and it's been fine (Touch Wood)

No. It would be a bit pointless if you could overcome it without major trauma.

Is the transponder in the key active or passive?
 

My 75 Tourer has just started playing me up with the immobiliser. What triggers the transponder chip when it is in the ignition lock? Is this a passive transponder or does it rely on a battery in the key? Is there a way of completely bypassing the immobiliser? This is now happening with both of my keys. HELP!!!!! :(

In what way is your car playing up? A list of the symptoms will help diagnose the problem as it may not be immoboliser related - for example other electrical gremlins can produce strange results.

Hi. The transponder doesn't rely on the battery. The coil around the ignition lock transmits a signal to the chip. The chip powers itself from this signal, and modulates the signal to talk to the immobiliser. The immobiliser also modulates the signal to talk to the chip. It's triggered as you turn the key from off, to accessory.

The battery is for the remote control: in the same box as the transponder, but not connected to it. The transponder has nothing to connect it to anything. You could take the battery out, and the transponder will still work. In fact early cars were meant to have one normal key an one key with only a transponder. Don't know whether this ever happened, but it would explain why so many early cars have only one key.

As I said earlier, the immobiliser would be a little pointless if it could be overcome without a good deal of effort: whoever wanted to steal your car would simply switch off the immobilser and drive your car away.

Diesel Intermittent Strating problems
 

Like many of us I have suffered the frustration, although rarely, of the starting problem. Usually resolves itself after being left alone for periods of time but still left me baffled. Tonight it happened again. RAC man turned up and immediately stated that he had dealt with this problem before. Popped the bonnet and tapped the top of the fuel pump. I turned the key and the old girl fired up immediately.
I have had my 75 since new (6 years) and 65,000 miles later I still believe it is one of the finest cars on the road. Hope this helps.

:welcome: to the Club Paul. :)

Thanks for the informative first post. As you have discovered - a sticky/failing underbonnet pump can cause starting issues. A quick tap unsticks it. Other fuel-related issues include the other fuel pump in-tank (where fitted) and the fuel filter which can come unscrewed (this is a simple fix with £2 spare part fitment to prevent repeat unscrewing).

Hope you enjoy your stay here - plenty to read up on and do if you haven't already seen. :)