Open Loop vs. Closed Loop?

[David K.]

What is the difference btwn. open and closed loop in the ecu? I cannot seem to recall, however I was reading a thread on ClubRSX that discussed O2 sensors and cel's. Specifically one member was stating that running no cat for long enough without an O2 simulator would result in the ecu going into open-loop mode, which would cause the car to run rich, hurting performance. Is this correct?

[DavidT]

Open lope basically means the ECU cannot correct the readings from the sensors it's inputing because they are out of range for the ECU to compensate for. So when that happens, the ECU goes into open loop mode and runs off it's PROM (Program Read Only Memory) instead of running off what it's sensors are outputing to it. Most cars tend to run richer (Especially Hondas) when they are in open loop mode. o2 sensors are a major cause to open and closed loop operation, because they output to the car's ECU how dirty the air is coming out of the vehicle.

In closed loop operation, the ECU is adjusting everything it can adjust on the car based on it's sensor outputs to the ECU. If the knock sensors senses knock, ECU will retard ignition. If o2 senses dirty air, ECU will try it's best to optimize combustion for cleaner air by advancing/retarding timing, VTC control, etc. Of course our cars are OBDII, meaning the ECU has control over a lot of stuff. In older vehicles OBD0 and OBDI the ECU can only control so many things so open loop mode didn't hender them as much.

If you want there is a lot of info on google if you do a search for "ECU open loop operation" At the beginning of this article is a perfect example of open loop vs. closed loop. http://www.jefferies-au.org/My16M/Closed_Loop_Operation.html

[David K.]

Good shit; thanks!

BTW - Now there is a member named "David L". Soon the Davids will own ephatch! Muahahahaha!!!!!:mad:

[andy]

I've been running around with my CEL on (eBay cat installed about
4K miles ago) for a while now.
I haven't noticed any lack of performance or seem to be running
"real" rich (I get about 260 miles before the fuel light comes on
and then usually end up putting 8.5-9 gallons of gas in, so that's
about 28-29 miles per gallon). I still want to get a CEL-eliminator,
but I'm honestly not sure if it's really needed.

[SiRman]

Would it be possible to check if the ecu is going into open loop with the use of a scan tool? It would be nice to get a factual test to show this is happening instead of just speculation and theories.
I'm just curious for future reference, no headers/testpipe here:(

[02HatchSI]

Good thread man... This knowledge is very handy :)

[fsugatorbait]

Originally posted by SiRman
Would it be possible to check if the ecu is going into open loop with the use of a scan tool? It would be nice to get a factual test to show this is happening instead of just speculation and theories.
I'm just curious for future reference, no headers/testpipe here:(

With the scan tool I have, im not sure how you would go about testing if its open or closed loop. I did however, run a graph of the two o2 sensor readings and found that the first sensor was at a pretty constant voltage, but the 2nd sensor ranged from .1x-.8x volts in a consistent pattern with the test pipe. I havent tested them in a while so im not sure how long its been like this, but this wasnt the readings I was getting when I first installed the pipe. btw I erase the DTC every week or so to refresh the ecu and get the CEL to go off, its back on now usually within 50 miles or so of driving, where as before it took a few days. Im gonna order the o2 sim later today to see if I can get rid of this little problem.

[SiRman]

Afer browsing through the service manual. Found that it says that if the sensor reads a abnormal reading for a certain period of time, the ECU stops running off the reading from the sensor and uses a default value from memory. Not sure what this value is but is probably somewhere in the middle of what it reads for a stock setup so that you are never too rich or too lean but will always be a liitle of one or the other.

[andy]

Originally posted by fsugatorbait
With the scan tool I have, im not sure how you would go about testing if its open or closed loop...

fsu, what data is available via that logging tool? I would think
that if you logged A/F, or maybe EGTs, you could determine what
is happening without CEL and with CEL. Like it runs leaner without
the CEL, richer with, that sort of thing.
If I'm getting this right, it sounds like "closed loop" mode means
that it is constantly learning/adjusting and so you should see some
sort of variance with what's going on when the CEL is off. When the
CEL is on, all the values should produce very little change.

Also, just some fyi info from Hondata:
[quote]
In closed loop operation the ECU uses one or more oxygen sensors as a feedback loop in order to adjust the fuel mixture. This gives the name

[fsugatorbait]

Unfortunately because we dont have a MAF sensor, the scan tool cant read the a/f ratio. If the ECU goes into open loop mode, how would you get it reset back into closed loop? I just ordered the o2 sim from casper electronics, so hopefully if my ecu has gone into open loop mode ill be able to reset it somehow to correct the problem, we'll see.

[myeverlovinsir]

Good info. I guess the only way to take the engine out of closed loop for sure on the dyno while tuning, would have to be done in the ECU (Programmable Unit). To the casual observer, there would be no tell tail sign that the ECU was in open or closed loop. If you were running in open loop I think a quick reset of the ECU could help, however how would you tell, short of buying an expensive scan tool?
I can't wait to see the programmable ECU and what it entails.

[DavidT]

OBDI and OBDII ECUs were designed to set off a CEL when it goes into Open loop mode. That's how you would know if it's in open lope if the CEL is on.

You can reset the open loop by resetting the ECU. This will be a short fix since the ECU will give a CEL within a few days. Pull the DTS code, fix the problem and CEL will go away and you're back in closed loop operation. BTW, the engine is in open loop until it reaches normal operating temp then it goes into closed loop.

[fsugatorbait]

Originally posted by DavidT
OBDI and OBDII ECUs were designed to set off a CEL when it goes into Open loop mode. That's how you would know if it's in open lope if the CEL is on.

You can reset the open loop by resetting the ECU. This will be a short fix since the ECU will give a CEL within a few days. Pull the DTS code, fix the problem and CEL will go away and you're back in closed loop operation. BTW, the engine is in open loop until it reaches normal operating temp then it goes into closed loop.

Interesting, I didnt notice any difference in performance after reseting the DTC with the scan tool. I wonder how much of a gain/loss you would experience with closed vs. open loop?

[David K.]

All I know is that my car is running quite rich; you can smell it. Plus on Jotech's dyno my A/F was hovering around 12:1-13:1. All of this with the cel on. Maybe it's my imagination, and I know butt-dyno's are not reliable, but when my cel sometimes goes off the car seems to pull harder and smoother, especially from lower RPMs.

[myeverlovinsir]

Originally posted by DavidT
OBDI and OBDII ECUs were designed to set off a CEL when it goes into Open loop mode. That's how you would know if it's in open lope if the CEL is on.

You can reset the open loop by resetting the ECU. This will be a short fix since the ECU will give a CEL within a few days. Pull the DTS code, fix the problem and CEL will go away and you're back in closed loop operation. BTW, the engine is in open loop until it reaches normal operating temp then it goes into closed loop.

The engine is also in Open loop under heavy load and there is no cel associated with that. A CEL is not a definitive way to determine Open loop. ECU can go in and out of Open loop without a CEL and the CEL may be based on poor emmissions from the 2nd heated oxygen sensor or any number of things other than Open loop.;)

From Hondata:
[QUOTE]The ECU won

[yellerep3]

o this is probably similar to a infinite for loop that has no ending opposed to one which captures a range of numbers for all the programmers

[k20beast]

how do i know if my car is running in open or closed loop???? i am running a straight pipe (i just took off exhaust from axle back) everything else is sock would that cause it to change????? im not too familiar with stuff like this???

[fsugatorbait]

Originally posted by k20beast
how do i know if my car is running in open or closed loop???? i am running a straight pipe (i just took off exhaust from axle back) everything else is sock would that cause it to change????? im not too familiar with stuff like this???


Is your CEL on? Am I reading your post right that you exhaust ends at the end of the b pipe? Say it aint so. :confused:
With the info ive read I think that the car after running for an extended period of time with the CEL will switch to open loop. I havent read of a way other than having a a/f gauge to be able to tell if your running in open or closed loop.

[David K.]

I called Caspers Electronics and gave them the cel code from my car, which I got scanned at Auto Zone. P1167 - front O2 sensor is trashed. The guy at Caspers said driving with your cel on for extended periods will definately cause the ecu to go into open-loop, thereby richening your A/F to the point that eventually you will foul your primary O2 sensor. This is what happened to me. My car definately has been running rich since the cel has been on, and now I need a new front O2 sensor; they're not cheap.

So a word of caution to everyone with a cel due to no cat - Get an O2 simulator.

[andy]

Originally posted by David K.
I called Caspers Electronics and gave them the cel code from my car, which I got scanned at Auto Zone. P1167 - front O2 sensor is trashed. The guy at Caspers said driving with your cel on for extended periods will definately cause the ecu to go into open-loop, thereby richening your A/F to the point that eventually you will foul your primary O2 sensor. This is what happened to me. My car definately has been running rich since the cel has been on, and now I need a new front O2 sensor; they're not cheap.

So a word of caution to everyone with a cel due to no cat - Get an O2 simulator.

Bummer. I think AdamNQuickCivic is selling his 02 sensors from his
K20A3 on eBay. You may want to PM him about it.
I've got probably 5K on that eBay cat and CEL is on all the time,
but both times it's been cleared it's been a P0420, secondary 02
sensor. So hopefully the first one has survived (I just got my
Caspers MIL eliminator in yesterday) long enough.

[andy]

Originally posted by andy
So hopefully the first one has survived (I just got my
Caspers MIL eliminator in yesterday) long enough.

Heh, quote myself. PostCount++. ;)

Anyway, put the sim in today. The ECU had been out long enough (just
got it back from Hondata) that the CEL was gone, but it stayed off
for about 40 miles. Of course, time will tell on this one, but
hopefully that'll do it. I'll update more over the next week or
so (it seemed like it took 50-200 miles for it to come back on
before).