Right - having some issue with a fluctuating AFR's. It appears that when the car in warming up and the pressure in the coolant system increases the AFRS settle at around 13.8AFR at idle.
I think that the header tank cap is faulty as I am losing the pressure in the system - When the pressure in the system is 5psi as opposed to 10psi the AFR's richen up at idle at 13.0.

Is this possible ? will a change in the coolant systems pressure change the AFR?


Thanks all.


Tim.