Toyota Fuel Sub-Systems (OPEN/CLOSED LOOP) Feedback Control
10-25-2006 | 01:18 PM
#1
Thread Starter
Member
SL Member
Joined: Jul 2006
Posts: 70
Toyota Fuel Sub-Systems (OPEN/CLOSED LOOP) Feedback Control
Cuppajack, myself, and many others were starting to go off topic in the ICE/Interior forum (In this thread) talking about the output from our ScanGauge II's OBD-II Scanners. Cuppajack noticed that most of the time, the ECU runs in Closed loop mode and that seemed curious to me.
In my past vehicles, closed loop mode was a state where the ECU ignored inputs from the O2 sensors, possibly the MAF sensor (depending on conditions), and other sensors and utilized stored 'Fuel delivery maps' to keep the engine running. Now, as you can imagine, trying to get a good mixture with limited or no sensor input is near impossible.
Ok quick, read Cuppajack's thought's below.
I took my xB out for a run through the paces and noticed the same behavior regarding the Open/Closed loop operation. In fact, the only time I saw Open loop operation was during situations where I was cruising at 40mph or hugher and let completely off the gas. Note: I never tried going W.O.T., yet ;) I'll test that on my way home from work to see if I get an open loop situation.
Anyway, as you can imagine, I was not happy about having the Scangauge tell me my xB was 95% of the time in closed loop mode. Was something wrong?
Then I started poking around the internet for some info on Toyota fuel system feedback loops.
I found this great publication on Toyota Emission Sub System Feedback Control Loops. This pub answers many of our questions.
Further, this pub may be of great use for those of you going with forced induction power adders. I understand from the brief reading of the F/I forum that these fuel systems can be a bugger to force feed ;)
As a paraphrase, in Closed loop operations the ECM utilizes many sensors input including the O2 sensors to keep the Air/Fuel ratio around a stoichiometric value (14.7 parts air to 1 part fuel). The various sensor inputs are utilized to trim the A/F ratio to keep as close to 14.7/1 as possible to keep the engine running clean as well as promote high catalyst efficiency.
(on a side note, I'm curious about whether the ECM doesn't try to lean burn to get even better emissions and power. I.E. 15.0/1 or so AFR... I know Toyota employs this technology in the Prius engine ... but, that's for another thread.)
Open loop operations occur when the ECM determines that the engine needs to run either more richly or leaner than 'ideal'. Situations when this may occur are Cold startup, WOT, heavy load conditions, heavy acceleration, and deceleration. In open loop mode, the ECM ignores O2 sensor output and controls fuel using other sensor input. Although the pub doesn't exactly explain what the other sensor inputs are ... You can probably guess they are the MAF, Intake air temp sensor, coolant temp sensor, etc. But, those are *my* guesses.
Well, I hope you all enjoy the pub like I did. Time to de-geek.
In my past vehicles, closed loop mode was a state where the ECU ignored inputs from the O2 sensors, possibly the MAF sensor (depending on conditions), and other sensors and utilized stored 'Fuel delivery maps' to keep the engine running. Now, as you can imagine, trying to get a good mixture with limited or no sensor input is near impossible.
Ok quick, read Cuppajack's thought's below.
Originally Posted by Cuppajack
Mmmm stoichiometric....
Speaking of AF ratios, O2 Sensors etc, What are peoples general "Fuel System Loop" and "timing advance" readings? I'm surprised to see my “Fuel System Loop” occasionally read as OPEN even after the car is fully warmed up and I’m cruising far below Wide-Open Throttle… Is this normal behavior? My Timing advance usually sits between 6-9 @ idle, though it will sometimes dip down to 1-2. It seems to hang-out around 30-35 when cruising.
I’ve usually got my display set to: LOOP, WATER TEMP, RPM, and in the last slot I toggle around between MPG, TIMING, and IA TEMP.
I have posted in a few threads about being disappointed w/ my fuel mileage, and was hoping the Scangauge would help me get to the bottom of it.
Speaking of AF ratios, O2 Sensors etc, What are peoples general "Fuel System Loop" and "timing advance" readings? I'm surprised to see my “Fuel System Loop” occasionally read as OPEN even after the car is fully warmed up and I’m cruising far below Wide-Open Throttle… Is this normal behavior? My Timing advance usually sits between 6-9 @ idle, though it will sometimes dip down to 1-2. It seems to hang-out around 30-35 when cruising.
I’ve usually got my display set to: LOOP, WATER TEMP, RPM, and in the last slot I toggle around between MPG, TIMING, and IA TEMP.
I have posted in a few threads about being disappointed w/ my fuel mileage, and was hoping the Scangauge would help me get to the bottom of it.
Anyway, as you can imagine, I was not happy about having the Scangauge tell me my xB was 95% of the time in closed loop mode. Was something wrong?
Then I started poking around the internet for some info on Toyota fuel system feedback loops.
I found this great publication on Toyota Emission Sub System Feedback Control Loops. This pub answers many of our questions.
Further, this pub may be of great use for those of you going with forced induction power adders. I understand from the brief reading of the F/I forum that these fuel systems can be a bugger to force feed ;)
As a paraphrase, in Closed loop operations the ECM utilizes many sensors input including the O2 sensors to keep the Air/Fuel ratio around a stoichiometric value (14.7 parts air to 1 part fuel). The various sensor inputs are utilized to trim the A/F ratio to keep as close to 14.7/1 as possible to keep the engine running clean as well as promote high catalyst efficiency.
(on a side note, I'm curious about whether the ECM doesn't try to lean burn to get even better emissions and power. I.E. 15.0/1 or so AFR... I know Toyota employs this technology in the Prius engine ... but, that's for another thread.)
Open loop operations occur when the ECM determines that the engine needs to run either more richly or leaner than 'ideal'. Situations when this may occur are Cold startup, WOT, heavy load conditions, heavy acceleration, and deceleration. In open loop mode, the ECM ignores O2 sensor output and controls fuel using other sensor input. Although the pub doesn't exactly explain what the other sensor inputs are ... You can probably guess they are the MAF, Intake air temp sensor, coolant temp sensor, etc. But, those are *my* guesses.
Well, I hope you all enjoy the pub like I did. Time to de-geek.
10-25-2006 | 09:30 PM
#4
Senior Member
SL Member
Team N.V.S.
Joined: Sep 2006
Posts: 152
From: Hollywood, CA
Holy crap!
I just checked out the site that hosts that file, and WOW! There is a TON of info there.
http://www.autoshop101.com/
I just checked out the site that hosts that file, and WOW! There is a TON of info there.
http://www.autoshop101.com/
Thread
Thread Starter
Forum
Replies
Last Post
evolving_machine
Scion tC 2G Drivetrain & Power
17
10-21-2023 02:16 PM
cid_mcdp
Maintenance & Car Care
4
01-05-2015 03:45 PM
