open or closed loop
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Freshman User
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open or closed loop
Hi Everyone
I was wondering is ther a way to tell if your truck is in closed loop or open loop for fuel? Is this also dependent on engine temp?
Thanks Seumas
97 Mazda b4000 230000KM gas hog
I was wondering is ther a way to tell if your truck is in closed loop or open loop for fuel? Is this also dependent on engine temp?
Thanks Seumas
97 Mazda b4000 230000KM gas hog
Post Fiend
Joined: Jan 2003
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From: Connecticut
Open loop occurs when the engine temperature is cold. It used to be that systems would not go into closed loop (i.e., using 02 and other sensor feedback) until a certain engine temperature was reached. This is especially true with the older EEC-IV systems.
However, many systems these days utilize heated O2 sensors, which allows them to be programmed to go into closed loop after a specified period of time, instead of waiting for a certain engine temp threshold to be attained.
However, many systems these days utilize heated O2 sensors, which allows them to be programmed to go into closed loop after a specified period of time, instead of waiting for a certain engine temp threshold to be attained.
Post Fiend
Joined: Jan 2003
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From: Connecticut
As far as I know, your system goes into closed loop around 30 seconds after startup, regardless of temperature. However, keep in mind that the computer (PCM) constantly engages in a "monitoring" of the system, and it will throw codes if your engine coolant temperature (ECT) sensor does not indicate a certain temperature within a certain time. If that happens, I believe the system defaults back to an open loop-type of status, using stored/inferred values from a table that is hard-programmed into the computer, making adjustments based on feedback from other sensor inputs (TPS, for example), but not from the 02 sensors.
This is my understanding of how the modern OBD-II system works with respect to open/closed loop operation. But like you, I am interested to hear what other people might have to say about the subject.
This is my understanding of how the modern OBD-II system works with respect to open/closed loop operation. But like you, I am interested to hear what other people might have to say about the subject.
Moderator
Joined: Jan 2004
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From: SW Va
That's about as I understand it Rockledge, although I didn't know heated O2 sensor systems would go into open loop as quickly as 30 seconds.
Thats nice to know.
His question was, "how do you know if it's in closed loop or not" & after thinking about it some, I don't know either, unless one monitor's the O2's output & the responding changing pulse width of the fuel injectors squirt signal.
Thats nice to know.
His question was, "how do you know if it's in closed loop or not" & after thinking about it some, I don't know either, unless one monitor's the O2's output & the responding changing pulse width of the fuel injectors squirt signal.
Hotshot
Joined: Aug 2002
Posts: 12,679
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From: BC, Canada
The only way that I know how to tell if it's on open or closed loop is to monitor the loop status on a scan tool.
The programming built into some PCMs is strange. Sometimes even with the engine warm it will go into open loop and then back to closed under certain conditions.
At a course I was at a while back we asked the instructor about this and he didn't have a good answer as to why they do that.
The programming built into some PCMs is strange. Sometimes even with the engine warm it will go into open loop and then back to closed under certain conditions.
At a course I was at a while back we asked the instructor about this and he didn't have a good answer as to why they do that.
Post Fiend
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Post Fiend
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On the older trucks I would say yes, the newer ones might wotk a little different since they are a little smarter.
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