Engine cuts out at a specific temperature

[steve-V8s]

I have been asked about a petrol engine vehicle that runs a closed loop control system and controls the idle speed with a throttle bypass valve. The car always starts from cold and runs fine until just below normal operating temperature at which point more times than not it cuts out and will not restart until the temperature has dropped (typically two minuets or so). If during the warm up it manages to get past the particular troublesome temperature point it then runs fine. The oxygen sensor has been changed and the throttle bypass disabled also tried a different ECU but no change. It seems it may fail at the point where it is switching from the warm up map to closed loop map.

Any ideas anybody ?

[steve-V8s]

Mr2Mike said:

Crank sensors can give odd temperature related faults. Worth a check anyway.

Thanks for that but have tried new crank and temp sensors

[steve-V8s]

GreenV8S said:

Does it only die if if it left to idle while it passes that critical temperature, or is it something that can be overcome by the driver?

No, nothing the driver can do about it. To the driver it feels as if the fuel pump or ignition has been switched off. With a view to eliminating this possibility the supply lines to these now have LEDs fitted for next time it stops, they are both powered from the ECU.

[steve-V8s]

Mr2Mike was on the money with this one, turned out to be the crank sensor which on this engine actually looks at the flywheel, it repeatably failed at a specific temperature. Diagnosis wasn’t helped by the ECU turning off the fuel after about four seconds of cranking with no result.