Open vs. Closed Loop

[FLAteam]

I played around with the Loop gauge today too and it seems mine is closed loop when TPS is greater than 0 and open loop when TPS is 0 (closed throttle). Does this seem normal?

[Jay2TheRescue]

Doesn't sound normal to me. What kind of vehicle do you have again?

-Jay

[FLAteam]

I've got a 03 Mitsubishi Lancer ES. I mean, would it matter if its open loop when its closed throttle? it goes right back to closed loop right when i apply the accelerator...

[Jay2TheRescue]

It just doesn't sound right... There's got to be something else going on there.

-Jay

[GasSavers_JoeBob]

I don't know about modern cars....but my '83 Cadillac goes into closed loop at 81 degrees centigrade coolant temp. The only thing that WOT does AFAIK is cut the A/C compressor.

[GasSavers_JoeBob]

Originally Posted by Improbcat

I'm trying to clarify something. From what I've read open loop is when the engine is using a default a/f mix, and closed loop is when it is using an a/f mix based on the reading of the O2 sensor and such.

O know the engine runs in open loop until it is warmed up.

Once warmed up should it stay in closed loop or should it be cycling between open and closed depending on throttle, gear, etc?

I ask because I was noticing that Box cycles back and forth, but I have no idea if that is normal or not.

You might check your wires going to the temp sender, O2 sender...hell...just check them all if you have a chance.

On my '83 Cad, I have had issues with wires that were old, heat and oil cracking the insulation, and rodents chewing on the insulation. Had the car 4 years, and I'm still finding bad wires!

I realize your car is pretty new compared to my Cad, but things still can happen...maybe a dirty connection, something snagged a wire at some time and broke some of the conductors...a little corrosion somewhere...

That's pretty cool...a car named after my favorite character from "Logan's Run"...

[Improbcat]

I had a chance this weekend to experiment more with this. By paying close attention I noticed Box goes into Open loop a half second before the instant mpg goes to 9999mpg. So apparently what I was seeing is the engine turning off as I coast in gear, and the scanguage was reading that as going into open loop. As soon as I touch the gas or put in the clutch and the engine turns back on it goes right back into closed loop.

[Jay2TheRescue]

I've heard the same, that SG will report open loop in DFCO, but my truck doesn't do that. I guess that's why my SG does not report DFCO as 9999 MPG. To confirm DFCO I either have to watch live O2 sensor data (DFCO O2=0) or ignition timing advance (DFCO = -10).

-Jay

[dkjones96]

The only EFI cars that don't go into open loop at(or near) WOT are usually those that don't have a fuel enrichment mode or those that come factory equipped with a wide-band O2 sensor.

Since manufacturers try to get you good HP numbers and good fuel economy at the same time, almost all vehicles have a fuel enrichment scheme of some sort for heavy load.