Open Loop/Closed Loop
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Tuned
Joined: Aug 2003
Posts: 346
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From: Eastern Virginia
Open Loop/Closed Loop
I am currently trying to fix a poor fuel mileage problem on my '96 F150 5.0L 5 speed. I have another post here also.
This truck has OBD II. I have a scanner but am not quite sure of some of the readings I am getting.
My question is: How do you know if the truck is in open loop or closed loop?
Right now the scanner shows "Fuel System 1-N/A" and "Fuel System 2-N/A".
I thought Fuel System 1 should say "Open" or "Closed".
Please help. Thanks!
This truck has OBD II. I have a scanner but am not quite sure of some of the readings I am getting.
My question is: How do you know if the truck is in open loop or closed loop?
Right now the scanner shows "Fuel System 1-N/A" and "Fuel System 2-N/A".
I thought Fuel System 1 should say "Open" or "Closed".
Please help. Thanks!
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Tuned
Joined: Aug 2003
Posts: 346
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From: Eastern Virginia
It is an Actron scanner. Yes, I had to enter all of the truck's info. Year, Make, Model, Engine, etc.
If i'm not mistaken it used to say open or closed. Now it just displays N/A for them both. What does this mean?
If i'm not mistaken it used to say open or closed. Now it just displays N/A for them both. What does this mean?
Posting Guru
Joined: Jun 1999
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Refer back to the scanners manual.....N/A could mean "Non-Apllicable" instead of "Non-Available"..... 1996.....the first "Full" year for OBD II......don't take much in context from what you see on the scanner.....go back to basics..you'll discover more.
Post Fiend
Joined: Nov 2001
Posts: 14,947
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From: Topsfield, MA
That can mean anything from a bad cat...to a bad 02 sensor after the cat....to bad wiring to that o2 sensor....to a poor running condition.....
...Likely the first few options.
...Likely the first few options.
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Tuned
Joined: Aug 2003
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From: Eastern Virginia
I will be replacing the O2 sensors shortly. The front two have been replaced about 60K miles ago....the rear one has never been replaced. Truck has 114K.
Does the rear sensor do anything other than "monitor" the cat? Or does it also control A/F ratio?
Does the rear sensor do anything other than "monitor" the cat? Or does it also control A/F ratio?
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Postmaster
Joined: Oct 2005
Posts: 3,034
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From: NJ
Rear O2 sensor monitors cat efficiency. If you are getting P0420 which is cat efficiency your converter is bad. Rear O2 sensor should detect zero oxygen past cat. If you get efficiency code you need a new converter. Might as well replace O2 sensors while in there.
Post Fiend
Joined: Nov 2001
Posts: 14,947
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From: Topsfield, MA
The rear o2 sensor in some applications (probably including this one) will fine tune the A/F ratio, but the computer relies mainly on the front o2's for A/F.
Those codes never isolate one problem vs another....if the sensor isn't reading correctly....how can it tell you that the cat is actually bad?....it can't.
Those codes never isolate one problem vs another....if the sensor isn't reading correctly....how can it tell you that the cat is actually bad?....it can't.
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