Closed loop mode. Is this true?

[oldmaninsc]

I saw this on another forum I belong to. The subject was about how to tell if a car is in "open loop" or "closed loop" and what factors are involved.

My question - are the following statements true?

"On EEC-IV PCMs ECT *can* be a factor as can HEGO switching frequency, but the primary factor is TIME.

With EEC-V/Power PC vehicles (all OBD-II and later) it's TIME only except for WOT when the PCM reverts to open loop."

Thanks for the input. I was always under the impression that the ECT had to be at a predetermined temp. before the PCM is in closed loop mode.

 

[brianl703]

Most vehicles go into closed loop as soon as the oxygen sensor is warm enough to start responding.

 

[OVERKILL]

On EEC-IV, the ECT must read 170F before the ECM will go into closed loop. This is well documented in the GUFB.

I am not sure with EEC-V.

 

[OrdnanceMarine]

Mine does as well as reported on my ScanGaugeII.

 

[GMBoy]

Originally Posted By: brianl703
Most vehicles go into closed loop as soon as the oxygen sensor is warm enough to start responding.



This is true, along with the ECT. You really have to be careful what you read on these internet forums. I get so frustrated at times with all the wrong info posted out there. Best bet? Get yourself a factory OEM service manual (not haynes and other offbrand ones) and read it.

 

[eljefino]

Or get a scan tool, my saturn goes into closed loop at around 120'F.

To me the definition allows semantics, many would argue that it's perfect, ultimate economy and going ten degrees cooler on a thermostat will knock it out. My angle is if the o2 is switching and adding to the fueling decisions, other factors like cold start enrichment can also come into play.

Others would argue with that saying if there's cold start enrichment, a narrowband o2 wouldn't see it or switch anyway.

 

[moribundman]

Originally Posted By: brianl703
Most vehicles go into closed loop as soon as the oxygen sensor is warm enough to start responding.


That applies most certainly to my Audi. I monitor both pre-cat O2 sensors.

 

[andyd]

I have no clue how long it takes the O2 sensor to heat up. Its heated so it prolly doesn't take too long. To test, I use a a DVOM set to dc volts. A good working O2 sensor swings between .2 and .8v every second or so. If it changes slowly or hangs midrange around .5 v it is bad.

 

[StevieC]

I know my Santa Fe goes into closed loop on my Scan-Gauge at different Water temperatures all the time. I think it's watching the 02 sensors and determines based on the readings and the mixture it knows it's feeding the engine and somehow determines when it's good to go.

 

[moribundman]

Originally Posted By: andyd
I have no clue how long it takes the O2 sensor to heat up. Its heated so it prolly doesn't take too long. To test, I use a a DVOM set to dc volts. A good working O2 sensor swings between .2 and .8v every second or so. If it changes slowly or hangs midrange around .5 v it is bad.


My O2 sensor monitor (a Voltmeter, really), dithers. After a while you get used to averaging the (digital) needle flicker to something that makes sense.

 

[GMBoy]

Originally Posted By: andyd
I have no clue how long it takes the O2 sensor to heat up. Its heated so it prolly doesn't take too long. To test, I use a a DVOM set to dc volts. A good working O2 sensor swings between .2 and .8v every second or so. If it changes slowly or hangs midrange around .5 v it is bad.



That's the hard way. Much easier and safer using a scan tool.

 

[BuickGN]

My TL goes into closed loop within 10 seconds of startup. I've heard this is part of the ULEV status.

The one GN we have that still uses a stock ECM takes a loooooooong time. It doesn't help that I drilled two small holes in the thermostat many years ago to "help" with cooling in the hot summers.

 

[oilyriser]

A heated sensor might be preheated if you turn the key to Run and wait a little while, then start the motor. I'll have to try this on my car one day.

 

[eljefino]

Have also heard of putting a heated o2 in an originally 1-wire setup, and splicing the heater element into an ignition hot wire.

 

[BuickGN]

The way the TL fires the 02s and cats off so quickly is running very rich with intentional misfires. I believe the timing is retarded also but not sure.

 

[Gary Allan]

Err..I didn't read into every detail here ..but you appear to be talking about closed loop being "enabled" ..not being in closed loop ..which unless you've got some trick system, you're not in all the time.

 

[andyd]

Mori, that's what the Bosch site said a good 'un behaves. GM Boy, I see no reason to buy a scan gauge for testing an O2 sensor when I have a dvom I'm just a shade tree hack.

 

[Buffman]

Originally Posted By: Gary Allan
Err..I didn't read into every detail here ..but you appear to be talking about closed loop being "enabled" ..not being in closed loop ..which unless you've got some trick system, you're not in all the time.


Guess it depends on the system. My LT1 has open loop which runs off preset tables for AFR, etc, until car is able to go to Closed Loop. Thereafter it Runs in closed loop, until car is shut off, or you go WOT. That in turn enables Power Enrichment Mode which is pretty much similiar to Open Loop (ignores 02 input for the most part)..

Heater 02 sensors usually are warm enough within minutes of Start. However depending on system, closed loop will vary. I set min coolant temp for closed loop at around 130* (which is close to factory). In conjuction with 02s giving ready state, and I do believe there is a timer, but no one has found that table in the code yet.

 

[Gary Allan]

My Jeep (and I assume all Mopar's of its vintage 2002) are only in closed loop at idle and at cruise. The long and short term adaptive tables operate it in any other state based on MAP readings. MAF systems are probably more articulate and discriminating ..but speed/density systems are numb.

In something other than highway (and not always there) ..or sitting still..it's in open loop more than closed.

 

[mechtech2]

You gotta have both warmed up to be in closed loop.