Right following on from a very informative discussion about air flow rates into a car engine I have a new problem. My Fiesta MK4 ECU has decided to no longer turn the radiator fan on. I have been to a mechanic and we have checked. He was able to make the fan run by instructing it to via his diagnostics machine and he as I is getting temperature readings from the diagnostics bus. So somewhere in the ECU it has decided to no longer turn the fan on. I am rather perturbed by this as clearly it is not just a blown output transistor as he got it to work via the ecu with manual instruction and the requuired information is coming in. It's like the things programming has changed.
I don't know if it is relevant but a few miles prior to this problem being discovered (on being stuck in traffic) my engine suddenly started running more smoothly and with less petrol (I had a few miles back accelerated to 3700 rpm which I rarely do so might of shook some rubbish out somewhere ?). Is it possible that the ecu reprogrammed to account for a change in the engine condition and forgot it has to activate the fan ? or has something burnt out. I am puzzled as the information is going in and it can be made to actuate the fan but it chooses not to.
He said I can have it sent away and fixed for about £200, but as this point I wonder, should I just get a new one, it's 12 years old, will anything else in it fail. Or is it a program fault. Educate me on ECU's