Engine won't restart once warm?

[Cyclone1]

Hi all,

My Fathers 97 Jag 4.0 Sovereign is having a few problems. From cold the car will start with no problems, but after taking the car for a drive of no more than half an hour, if he switches the engine off and then tries to restart it, it will not restart?? This doesn't happen all of the time, but is starting to gradually get worse. He then has to wait for a couple of hours before the car will restart again. He has taken the car to his local dealer, but unfortunately every time he's took it there the car has behaved perfectly!! so they are unable to diagnose the problem. They have mentioned that it may be an ECU fault / replacement. Personally I think that it may be something simpler like a short somewhere or a sensor failing......

Hope someone can help....

[IOLAIRE]

Cyclone1 said:

Hi all, My Fathers 97 Jag 4.0 Sovereign is having a few problems. From cold the car will start with no problems, but after taking the car for a drive of no more than half an hour, if he switches the engine off and then tries to restart it, it will not restart?? This doesn't happen all of the time, but is starting to gradually get worse. He then has to wait for a couple of hours before the car will restart again. He has taken the car to his local dealer, but unfortunately every time he's took it there the car has behaved perfectly!! so they are unable to diagnose the problem. They have mentioned that it may be an ECU fault / replacement. Personally I think that it may be something simpler like a short somewhere or a sensor failing...... Hope someone can help....

There's a strong possibility it's the temperature sensor that's leaning the mixture back too far when it warms up; I have had this with a couple of XJs.
As the engine warms up the resistance inside the sensor alters to weaken the mixture, if it goes too far it will not start until it cools down again.
The other thing to check is the lambda sensors, I think from memory there are two on this engine and they're very accessible; when the engine fails to start, unplug them and try it. If it starts plug one in at a time to find out which is faulty.

[Cyclone1]

IOLAIRE,

Thanks for the reply, I will try the lambda sensors and see if it's this. Which temperature sensor is it that you referred too, and approximately where is it located?

Thanks

[IOLAIRE]

Cyclone1 said:

IOLAIRE, Thanks for the reply, I will try the lambda sensors and see if it's this. Which temperature sensor is it that you referred too, and approximately where is it located? Thanks

I'm really stretching my memory here, but I think it's in the front area of the inlet manifold; it is situated in the water gallery that runs through the inlet manifold and takes the temperature from the engine coolant.
It will have a multi plug connected to it and will probably be a Bosch sensor.
If you're near a Jag dealer ask the store to print you out a copy of the page that shows the sensors and you can track it down from there.
Better still get your hands on a workshop manual or a repair CD.