850 engine cuts out

Tricky one!!

I would suggest you check the connections at the ignition coil, and under-mounted amp, and especially the earth ring connector that is trapped under one of the bolts. Remove the coil unit entirely, as its often painted under neath and the earth connection is less than ideal electrically.

Also check the King HT lead is properly restrained in the clips around the air filter, and the Air temp sensor wiring is routed as far away from the HT lead as possible.

Also check the Cam Position Sensor (CPS) wiring plug on the end of the exhaust cam, and the Crank Angle Sensor (CAS) plug wiring below it.

I am mystifed by your weird temp gauge readings,- it may well the ECU is being spiked by stray HT, but it should restart straight away though.

Tim..

Thanks Tim, I had checked the wiring but not the coil earth - I will do that. It's tricky to find a fault that has gone...

But it's not entirely gone. You have a code stored in the ECU that caused the Lambda light. That code should point you in the correct direction.

Thanks guys. Today the car stopped again, but I had my trusty voltmeter with me. I measured the voltage on the coil: ignition on - nothing. Cranking - 12v to chassis on both red and blue wires, of course no voltage across the coil. I tried earthing the coil body/ amplifier heatsink - no change. I don't expect either coil connection to be grounded but the fault must be in whatever it is that drives the coil amplifier. Time, I thought, to read the fault codes: Socket A pins 2 and 3 give 1-1-1, socket B pin 5 gives 1-1-1. None of the other pins give any flashes. I hope this means something to someone... the temp. gauge was doing the same thing: switch on, the needle goes to halfway, pauses for second, then goes right up, pauses for a few seconds then falls to zero. After an hour and a half, as I was attaching the tow rope, my wife tried the key and she fired up, drove home with no problems. I didn't mention it before, but the central locking gives trouble in damp weather, especially the tailgate, and the remote often will not lock the doors although it will unlock them after I have locked them manually. Could this be an immobiliser fault? Where is the immobilser located, and can I disable it?

No, it wont be an immobilizer fault, as it is inhibited whilst the engine is running.

Seeing as you had no +12v at the coil with key on, I would head straight for the main relay (underside of fuse box) Sounds to me that the ECU is not powered up when it dies. - dry joint in the relay.

If you can- check for +5v at one of the engine sensors (pin 1 if its a 3 pin connector) the next time it quits. If 0v the ECU is not powered.

Either replace the relay, or open it up and resolder the PCB.

Tim..

Hi again just an update... the ECU was still powered because it started the fuel pump briefly when the key was turned. Someone on another forum suggested the coolant temperature sender - I replaced that, and the thermostat as well because you have to remove the elbow to get at the sender, and the car has not broken down for 40 miles so far (it wouldn't do more than 10 miles before). The only trouble is that the idle is now down to 550 RPM hot or cold, and it stalls easily.... I think I'll start by cleaning the idle valve, but what next? Cheers, Alan