Open/Closed Loop and Scan Gauge
 

A quick question - I had an erratic FE reading on my scangauge in my Saturn yesterday (I usually see 5.8ish litres per 100km's, but I suddenly had 9.9 litres per 100km's - today was back to normal, not sure why it showed so bad yesterday, the car ran exactly the same as always). Maybe the SG lost its marbles for a day. But I digress.

So I had changed the parameters I was monitoring on the SG to see if something was amiss that may have caused my FE reading change. I monitored Intake Air Temp, Cooloant Temp, Litres per 100 km's and Open/Closed Loop operation. I noticed whenever the injectors shut off, that the car slipped into open loop for the duration the injectors were off. It went Closed loop as soon as I pressed the throttle again.

Does this make sense? I guess the ECU goes open loop because since there is no fuel flow, checking for a rich/lean condition is a moot point. Maybe it would throw a code if it didn't go open loop. Please forgive my ignorance on the subject, just trying to make sense of it all.

Thanks

Rick

I see the same thing with my Jeep. I think it must be the way most ECUs are programmed. I suspect it's the only way the logic in the computer will allow it to shut off the injector pulses, since it is doing the shut off based on RPM and throttle position alone. I don't worry about it, since the injectors are off I'm getting infinite mileage anyway:)

Good to hear its more commonplace. The more I think about it, it does make sense that this happens.

Cool.

My FE readings today were bang on again...wish I could figure out why they were so high that one day.

Rick

That is how it works. No fuel = open loop. :)