gpsman1 and glennb — As I understand it, the O2 sensor measures the amount of O2 in the exhaust gases, and the MAP (Manifold Absolute Pressure) and and Air Flow or MAF (Mass Air Flow) gauges in the intake air path compute the O2 being taken into the cylinders. When operating closed-loop with fuel present, running tests are made to determine whether or not stoichiometric balance conditions are being met, and if not, adjustments are made to the air/fuel ratio going into the cylinders so as to achieve stoichiometric balance. This ensures just the right amount of oxygen for the fuel used. I don't see how the feedback loop can be kept closed if no fuel is being injected. I may be mistaken, but can you explain how and why?

Stan

 

I think we are talking technical semantics. The injectors are injecting based on several inputs to the PCM.....when one of those inputs is O2 measured in the exhaust.....then the system is termed "closed loop". (Specifically, the 'chemical reaction loop' is completed or "closed") Regardless of how balanced the reaction is. Cold O2 sensors are not accurate so the system "ignores" them until they are ......and then moves from "open" to "closed" loop - don't know if the system knows of other conditions that it should be running "open loop"- such as coasting with no fuel injected.

 

glennb — I don't think this is semantics. The loop that gets "closed" is not the chemical reaction loop but the electronic feedback control system's loop. This feedback system could go unstable if its control loop was closed before the needed stability criteria were met. The sensor data (including such things as catalyst temperature, etc.) are monitored by the engine control system, and used to determine when the control loop should be closed. I'm surprised to find that it says "closed" even when no combustion is occurring. It may say closed, but perhaps it is not actually closing the loop?

Stan

 

Or, it is closing the loop but ignoring the input when it is out-of-range.....again, I assume the PCM takes in a host inputs before it decides what to inject.....acknowledging the signal from the O2 sensor (but not necessarily using it alone) "closes the loop" from the particular language I've seen in the manual (some might choose to call that "open loop").....just my 2cents, thought it might avoid some confusion in the discussion

 

glennb — If the PCM is ignoring the sensor input, then the sensor is no longer in the feedback control loop — the loop is "open." Indeed, if there is no fuel going into the spinning ICE, the amount of O2 in the exhaust air will be the same as in the intake air; and if the loop were closed (i.e., the O2 sensor data were being used), fuel injection would have to start to bring the O2 level down. But I've pushed this point far enough! Can we believe the FEH's indication that zero fuel is indeed being used?

Stan

 

I know my engine temperature falls like a rock during open loop, downhill coasting. Like from 190'F to 140'F in just a couple of minutes.

So if info can be inferred.... at least there is indirect evidence.
It takes fuel to keep an engine hot.

 

gpsman1 — Okay, your argument is persuasive! (That is, unless the outside temperature was cold enough to cause the heating of the passenger compartment to result in the rapid cooling of the ICE that you observed. For example, in my TCH in winter, I have seen the ICE's coolant temperature drop surprisingly rapidly while "off" — maybe 5 deg. Celsius per minute.) Until we have evidence to the contrary, I'll accept that the FEH's ICE is not using fuel under the condition we are discussing, even though the readout says closed-loop.

Stan

 

No, heater to the cabin was off. Once the cabin is warm ( 60's ) the bodies inside do a pretty good job keeping it there. Outdoors it was maybe 35-40'F.

 

The fact that the FEH apparently indicates "closed-loop" while coasting in fuel-cut mode throws a spanner in the works for Ron DeLong of Linear-Logic (the ScanGauge manufacturer). Ron was planning (hoping?) to use open-loop operation as one of the necessary conditions to tell that the ICE was in fuel-cut mode. I wonder if there are other vehicles that do the same?

Stan

 

Stan, I have NEVER seen closed loop and infinate MPG at the same time.
Coasting in Fuel-Cut is always "open loop". Car must be in D or L. Fuel is burned in N.