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.

 

What car, model year is this on?

 

If anything you would have overheating issues, as the lower the pressure, the lower the boiling point.

Martin

 

Hi 3 door cosworth - No overheating issues. It's really strange.



Thanks.


Tim.

 

What afr gauge are you using ?

 

PLX, It is accurate as I have tested it against a couple of other units . you can also see the change in the fueling on the lambda sensor. (Soot)



Tim.

 

I would have thought the car would adjust fuelling from cold air map to hot but cannot see it being directly related to pressure in the water system as nothing is reading water pressure.

What management are you on?

I think you are going to need to replace pressure can and see if that solves the pressure change, then rule out head gasket issues etc.

Where are you based? I suspect someone like Mark Shead or MSD could diagnose and fix quite easily.

 

Knackered coolant temp sensor?

 

Sounds that way or maybe the loom corroding?

Has the connector at firewall been checked / replaced as is a common failure

 

Thanks all - will test this morning with new cap and see if pressure holds. The engine has been rebuild and does not use coolant or oil. The sensor are all new and a new loom was picked from Auto dynamix .
So we shall see, Thanks will let you know how I go.


Best.


Tim

 

Double check the Engine Earth too

 

A little normal change in pressure in the cooling system should in no way whatsoever affect AFR's

The only difference there is when it is at 10psi, presumably the engine is substantially warmer than when it was at 5psi ?

Of course engine temperature could affect AFR's