Open Loop/Closed Loop
 

I was aware that DFCO doesn't come into effect until the engine is sufficiently warmed up and thought it was a function of the Open Loop/Closed Loop. This morning I set the ScanGauge up to show me Coolant Temperature and Loop ststus, with a view to finding out at what temperature the changeover occurred, but almost from the get go the system was cycling between Open and Closed Loop. This happened even before Blue dashboard Engine Temp light went out.
I take it there is more in play than I first though?

More than likely your vehicle has a heated O2 sensor. O2 sensors only work reliably in a certain temperature range, and many now have heaters built in to get them up to temperature faster.

Thank you. I checked my schematics and the O2 sensors are heated. So that brings me to the next question, what else inhibits the fuel system from going into DFCO mode until engine gets warm? Is it just the coolant temperature? Or is there even more Black Magic at work?

There is usually an additional air control valve that gives you faster idle speeds during warm up. Possibly when that valve is open and until it closes to normal idle position there could be an affect on DFCO.

It's most likely that DFCO will not function until the engine is close to operating temperature.

That is what I have found. My coolant low temp light goes out at 55°C and about 60°C the DFCO starts to operate.

Do you have an older Scangauge that can't 'see' DFCO on its own? I had to use the Loop gauge to determine DFCO operation in the past, but after the firmware update, the instant MPG gauge goes 9999.9 now when it happens.

My ScanGauge shows DFCO. 999.9 mpg, as you say. What I was trying to determine was, at what coolant temperature system went from Open Loop to Closed Loop, thinking that as I monitor coolant temperature that would give an indication of how far away I was from switching to DFCO. But Closed Loop doesn't appear the sole factor in determining when DFCO comes into operation.

Funny as you started this topic, I noticed the other morning on a cold start, the instant mpg reading, which usually reads 999.9 mpg when you lift off, just read --- instead, below a certain speed. Like you say, it's still using fuel to warm up first thing.

Yes, it takes me about a mile and a half until DFCO starts to work. Up until then the instantaneous fuel figure is the same as for tick over.

Never thought to monitor temperature and loop together, but I notice the loop can close really quickly after a cold start up.

Honest cars are going to operate in a manner to maximize the emissions reduction, and only CO2 is directly related to the amount of fuel used. Thus the early closing of the fuel trim loop and no DFCO while the catalytic converter can still be cold.