When does Open Loop become Close Loop

LeFrog · Post by **LeFrog** » 03 Sep 2004, 11:13

Related to my post titled 'Is my temperature reading normal?'
Assuming the ECU has an open and closed loop mode, what is the trigger for the closed loop to kick in? Is it the water temperature? If so, what temperature?

tomsheppard · Post by **tomsheppard** » 03 Sep 2004, 13:34

Who is assuming that there is an open loop mode? Closed loop occurs when the system is controlled by a feedback mechanism, eg. the temperature sensor. The closed loop works continuously.

Post by **RichardW** » 03 Sep 2004, 14:00

I think Le Frog is referring to the lambda sensing circuit running 'open loop'. AFAIK, catalysed cars ignore the reading from the lambda sensor on cold start until the engine temperature comes up to the point where the cold start enrichment switches off - otherwise the lambda reads rich, and the ECU would cut back the fuel on the main injectors to try and balance things, and then the engine would stall as the 'choke' would not have any effect. I guess this happens somewhere about 60°C? The ECU uses a different sender to the gauge and warning lights though.
Back to the previous post about temperature gauge reading - if the gauge jumps about in normal driving, and doesn't hold onto a minimum temperature (eg 80°C on both my TDs), only rising when working hard or sitting in traffic, then it's probable the thermostat has failed partially open or has gone 'lazy'.

LeFrog · Post by **LeFrog** » 03 Sep 2004, 14:38

You're right Richard, I'm refering to the Oxygen sensor. My understanding is that when the ECU is in 'Open Loop' mode, it refers to it's preprogrammed instructions about how lean/rich to run. i.e., it doesn't care about the Oxygen reading.
My question asking when the 'Closed Loop' kicks in is an attempt to discover whether I'm in fact running in 'Closed Loop' whenever my temperature gauge is less than normal (whatever that is). If so, this may explain the less than perfect idle when the the gauge is reading low.