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Old 01-15-2015, 09:47 AM   #1
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Closed Loop Control?

2002 ZTEC 2.0 DOHC. At what CHT temperature increasing does the PCM change to closed loop control? And at what CHT temp decreasing does it drop out? I put in a new thermostate housing and noticed the dash engine temp gage is really low for most of my 50 mile commute in the morning. I put the scanner on this morning and stayed at ~170 degrees until I was cruising at 70mph for 5 minutes and finally saw 199F. The housing came with a thermostate already in the housing.


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Old 01-15-2015, 02:02 PM   #2
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You confused me.

Typical references of "open loop" verses "closed loop" are used to describe the PCM's mode of how it is adjusting air/fuel flow rates. The only/primary sensor involved in this process is the O2 sensor; however other sensors such as CHT might also be involved in the process. I am guessing you are not asking about this (are you???) and are instead asking about temperatures that the engine cooling system opens and closes the thermostat?

BTW: once started with cold engine, my car switches into Closed Loop mode very quick. Guessing about 30 seconds or less.

Nothing in your story seems odd to me. Weather there this morning was cool/cold, so those readings seem normal.

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Originally Posted by 1turbofocus View Post
Low speed (cooling fans) isnt set to come on till 220 and high speed (cooling fans) comes on a 232 Deg and that straight out of what a stock ECU is set to

Stock thurmostat wont open till 192 Deg

Tom
I think the quote above should answer most of your questions. If not, come on back.
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Old 01-15-2015, 04:22 PM   #3
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My understanding is the coolant temp is the parameter that signals the fuel strategy into closed loop. The O2 sensors respond to what the fuel strategy is doing.

I am able to see when the system goes into closed loop on my scanner and will see when it changes on the ride home tonight.
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Old 01-15-2015, 04:42 PM   #4
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I do not know the system well enuf to answer or argue any details of how the PCM decides when to enter or exit Open/Closed loop.

My belief is/was the car enters into Closed loop soon after start-up and stays in this mode as long as no problems are detected by other sensors. It may however switch during WOT or similar conditions (??).

Very soon (30 seconds) after engine-on I have seen my car switch from Open to Closed loop and I have never seen it go back into Open loop (based on the few times I have looked).

We need an expert who knows if and how the CHT influences the Open/Closed loop modes. I will PM TurboTom and ask him to review this thread.
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Old 01-15-2015, 04:56 PM   #5
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The ECU looks at a few things , time , ECT , EGT to switch from open loop to closed loop even if the ECT isnt to what it should be you will still switch to closed loop at a given time

If you installed anything less then a 180 deg thermostat then you need to change it to a 180 in some rare occasions some ECU with a 180 needs to ECT changed in the tune for the cooler thermostat

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Old 01-15-2015, 10:44 PM   #6
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Within 1 minute of starting the engine it went to closed loop, and btw coolant temp was at ~80F. I'll have to check into what t-state is in the new housing.

Thanks guys
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Old 01-16-2015, 10:21 AM   #7
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Thank you Tom! Geezzz, crazy fast response, you rock!

Plugged in my ELM327 (bluetooth) to OBD and used Android App Torque...

First engine start of day (engine cold) and here are the results;

Key On Engine Off
Fuel Status: Open Loop (Low Temp)

Key On Engine On
<<< 10 Seconds after engine was turned on >>>
Fuel Status changed.
Fuel Status: Closed Loop (using O2)

The PCM obviously does not care too much about CHT/ECT -or- does not prevent Closed Loop mode if ECT is cold.

It stayed in Closed Loop during my 15 minute drive. I forgot to do a WOT to see if it would change into Open Loop.
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Old 01-17-2015, 01:49 PM   #8
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O2's have nothing to do with Open Loop or Closed loop.


It's time based, temp based and throttle position based, and time since last start/soak time.



People put too much stock in what the O2's do, which isn't much really. They are an after the fact sensor only, second order sensor.
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Old 01-17-2015, 02:29 PM   #9
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Quote:
Originally Posted by Marde View Post
I do not know the system well enuf to answer or argue any details of how the PCM decides when to enter or exit Open/Closed loop.
Quote:
Originally Posted by iminhell View Post
O2's have nothing to do with Open Loop or Closed loop.

It's time based, temp based and throttle position based, and time since last start/soak time.

People put too much stock in what the O2's do, which isn't much really. They are an after the fact sensor only, second order sensor.
This post is meant to help me and others learn; not to argue with you; I am a fan of your work here, thank you.

I would bet that disconnecting the upstream O2 sensor would knock the fuel system out of Closed loop and into Open Loop... if so, the O2 sensor DOES have something to do with it.

Edit: O2 sensor is most definitely a primary sensor while in Closed Loop -and- if defective, would push system into Open Loop. Even the scan tool software reports "Fuel Status: Closed Loop (using O2)". Previously shown above in blue font.

time based: only thing I know is my car waits 10 seconds (while PCM is checking other sensors and heating O2 sensors right?) before entering Closed Loop.

temp based: my car entered into Closed Loop on a cold engine/45 F, if low Temps (ECT/MAF Temp adjusted?) prevent Closed Loop, it is something lower than 45 F. This goes back to the OP's question; and nothing I have seen so far proves that Open/Closed Loop is toggled because of ECT.

TPS based: I guessed this earlier, but have not tried WOT yet to see if my (cheapo) scan tool would detect a moment/switch into Open Loop. Instead of Visual, maybe I could datalog this PID (Fuel System Status) in a future test.
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Last edited by Marde; 01-17-2015 at 03:47 PM.
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Old 01-17-2015, 05:35 PM   #10
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Quote:
Originally Posted by Marde View Post
TPS based: I guessed this earlier, but have not tried WOT yet to see if my (cheapo) scan tool would detect a moment/switch into Open Loop. Instead of Visual, maybe I could datalog this PID (Fuel System Status) in a future test.
Just got back from driving it like I stole it, that was very fun. Need to do that more.

WOT or similar will pull it out of Closed Loop -and- goes into Open Loop. The message was "Open Loop Engine Load/Deceleration". It snaps back into Closed Loop pretty fast, but one time it took about 5 seconds.
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