Open vs. Closed Loop - Fuelly Forums

Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

Reply
 
Thread Tools Display Modes
 
Old 09-18-2008, 05:42 AM   #1
Registered Member
 
Join Date: Nov 2007
Posts: 135
Country: United States
Open vs. Closed Loop

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.
__________________

__________________

Think inside the Box!
Improbcat is offline   Reply With Quote
Old 09-18-2008, 06:11 AM   #2
Registered Member
 
Join Date: Jul 2007
Posts: 280
Country: United States
I was always under the understand that once in closed loop (when warmed up) that it stayed there except for WOT. Probably about 90-100% of throttle it ignores the O2 and just starts dumping in extra fuel.

I've never had a meter to actually verify this on any of my cars though. My father has a Chevy scanner and I know our trucks stay closed once they close as does his Caprice.

I'm not sure about your car since it's a lot newer, I'm sure most new cars just read the TPS, but on my old Audi there was actually a switch at the end of the physical throttle movement, if this was adjusted too far in you could be hitting at 50-60% throttle maybe? Or actually just check your TPS, measure resistance at 0-50-100% and see if it lines up with what others report.
__________________

itjstagame is offline   Reply With Quote
Old 09-18-2008, 06:29 AM   #3
Site Team / Moderator
 
Jay2TheRescue's Avatar
 
Join Date: Sep 2008
Location: Northern Virginia
Posts: 4,657
Country: United States
Location: Northern Virginia
Arrow

Quote:
Originally Posted by itjstagame View Post
I'm not sure about your car since it's a lot newer, I'm sure most new cars just read the TPS, but on my old Audi there was actually a switch at the end of the physical throttle movement.
Are you sure that's what that switch is for? My old 1980 Bonneville had a switch at the end of the throttle travel as well, when the switch was activated the transmission kicked down to a lower gear. That switch seems kinda redundant on a newer car as the computer already knows how much the pedal is being pushed from the TPS.

-Jay
__________________






Jay2TheRescue is offline   Reply With Quote
Old 09-18-2008, 06:45 AM   #4
Registered Member
 
Join Date: Jul 2007
Posts: 280
Country: United States
Right that's why I suggested to check the TPS. Well my Audi was manual and I know for a fact when the switch was pressed that it goes to WOT, but the Audi isn't a good example of anything because it didn't have a TPS and measure fuel requirements with a flapper :-).
itjstagame is offline   Reply With Quote
Old 09-18-2008, 07:31 AM   #5
Registered Member
 
palemelanesian's Avatar
 
Join Date: Apr 2013
Posts: 364
Country: United States
My 1996 Civic goes to Closed Loop after about 10 seconds from a cold start. Warm start and it's almost immediate. It switches to Open Loop above about 95% load / throttle.

...according to Scangauge.
palemelanesian is offline   Reply With Quote
Old 09-18-2008, 10:18 AM   #6
Registered Member
 
Join Date: Nov 2007
Posts: 135
Country: United States
Would a bad TPS possibly cause this? Also the idle is uneven when in neutral and stopped, it drops til the engine nearly stalls then jumps back up to over 1000rpms, then drops steadily again.
__________________

Think inside the Box!
Improbcat is offline   Reply With Quote
Old 09-18-2008, 04:07 PM   #7
Registered Member
 
Join Date: Jun 2008
Posts: 256
Country: United States
Quote:
Originally Posted by itjstagame View Post
I was always under the understand that once in closed loop (when warmed up) that it stayed there except for WOT. Probably about 90-100% of throttle it ignores the O2 and just starts dumping in extra fuel.
This is how the 02 sensor is supposed to work. Sometimes it will even go to closed loop before the engine is totally warmed up to normal running temp, as long as it does not need the extra rich fuel mixture.

Could be something wrong with the 02 sensor if it is continually running open loop and wasting fuel.
__________________
Dave
GasSavers_GasUser is offline   Reply With Quote
Old 09-18-2008, 07:28 PM   #8
Site Team / Moderator
 
Jay2TheRescue's Avatar
 
Join Date: Sep 2008
Location: Northern Virginia
Posts: 4,657
Country: United States
Location: Northern Virginia
Almost sounds like a vacuum leak somewhere. My grandfather's Grand Marquis did that and the dealer found a cracked vacuum tee under the hood.

-Jay
__________________






Jay2TheRescue is offline   Reply With Quote
Old 09-18-2008, 07:42 PM   #9
Registered Member
 
2000mc's Avatar
 
Join Date: Oct 2007
Posts: 72
Country: United States
Quote:
Originally Posted by Improbcat View Post
Would a bad TPS possibly cause this? Also the idle is uneven when in neutral and stopped, it drops til the engine nearly stalls then jumps back up to over 1000rpms, then drops steadily again.

bulletin - EG012-04

INTERMITTENT ROUGH OR LOW
ENGINE IDLE AT A STOP

A small number of 2004 model year Scion xA and Scion xB vehicles equipped with manual transmissions may experience an intermittent rough or low engine idle at a stop due to a possible misadjusted throttle cable.
__________________
2000mc is offline   Reply With Quote
Old 09-19-2008, 05:58 AM   #10
Registered Member
 
Join Date: Nov 2007
Posts: 135
Country: United States
Quote:
Originally Posted by 2000mc View Post
bulletin - EG012-04

INTERMITTENT ROUGH OR LOW
ENGINE IDLE AT A STOP

A small number of 2004 model year Scion xA and Scion xB vehicles equipped with manual transmissions may experience an intermittent rough or low engine idle at a stop due to a possible misadjusted throttle cable.

That sounds exactly like my car. I dug up a copy of that TSB online and will have to look into it.
Sadly it also sounds like I've got another issue what with the going in and out of closed loop.
__________________

__________________

Think inside the Box!
Improbcat is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Default Car? jerryc41 Fuelly Web Support and Community News 2 04-04-2011 03:32 PM
Vehicles excluded from graph? jostlehim Fuelly Web Support and Community News 4 12-11-2010 03:24 PM
Synthetic motor oils and MPG TONYPR70 General Fuel Topics 13 01-06-2009 06:36 AM
BMW C.L.E.V.E.R. Concept MetroMPG General Fuel Topics 4 04-24-2006 11:59 PM

Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 11:59 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.