Closed Loop Mode
 

Ok, I just got my scangauge installed and have a question about the Open/Closed Loop mode. While I know what they signify, I don't know why my Jeep goes into Closed mode so quickly. Example, on a 45 degree morning, startup, wait about 30 seconds while I get my seatbelt on, adjust the wipers and such, and pull out of the parking lot, and it goes into closed loop as I pull out. The Temp needle hasn't pulled off of the 110 degree mark (sorry, didn't get the water temp off of the Scangauge this morning).

On the upside - my scangauge says that I got an average 21.7 MPG for my last 90 mile trip to my relatives house in moderate highway traffic, heavy rain and no aeromods as of yet.

I'm not seeing the problem here, closed loop is good. Open loop is really only needed for starting, extra power, and drivability under certain circumstances.

My brain is obviously not working right this morning, so I'm gonna have to ask...what exactly is "open loop" and "closed loop"? I'm almost positive I've seen it explained elsewhere, but could somebody give me a refresher, please?

Very simply, open loop is when you are not running at stoichiometric air/fuel ratios. Your vehicle is using the maf or map sensor in combination with a few other sensors to determine how much fuel to inject. In this mode you are almost always injecting more fuel than necessary (except in a fuel cutoff situation, in gear deceleration for instance). During closed loop the fuel injection is based mainly off of the oxygen sensor in the exhaust. It holds the air/fuel ratio to stoichiometric ratios and is in general more efficient than running in open loop.

Definately not a problem, I just wanted to know if it was unusual for an unwarmed vehicle to go into closed loop so quickly.

It would not be unusual at all for a car with a wideband O2 sensor to enter closed loop mode quickly. With the wideband the closed loop can control warmup at a richer AFR and then transition to a leaner AFR when warmed up. With a wideband there is almost no reason to stay open loop except start up and maybe after start enrichment because AFR can be controlled across a wide range. With a narrowband O2 sensor it wouldn't make a lot of sense for the car to enter closed loop until the engine is warm because you will only be correcting to 14.7 AFR. My 2 cents

JeepNmpg2 -

Can you find out how many wires are attached to your exhaust manifold 02 sensor(s)? You could have a wideband sensor as mobythevan says, or you could have a heated narrowband 02 sensor. I think wideband are also always heated(?). In both cases it would go into closed-loop faster.

CarloSW2

O2 Sensor
 

Sure, when I get off work, I'll go and look. Do you know which sensor I should look at, I think mine has two or three O2 sensors (1 or 2 on the manifold and 1 after the cat).

-Andrew

JeepNmpg2 -

Thanks, the one(s) on the manifold. Those are the ones that are most important for closed-loop AFR (Air/Fuel Ratio).

CarloSW2

It's probably worth noting that stoichiometric ratio (lambda 1.0) is the peak thermal reaction, but it is not the best place to run an engine for either fuel economy or power.

Best economy is leaner (around 1.05 lambda), best power is richer (around .86 lambda, but with a lot of variation depending on engine design).

The only reason that vehicles target stoich is emissions. Stoich is the highest EGT, and that gas temp is needed for the CAT (which has a very narrow efficiency band). Also, it is a good spot on the HC, CO2, NOx emissions curve.

As a practical matter, closed loop IS usually more efficient than open loop because the cars always error rich open loop.

Generally speaking, vehicles with heated narrowband sensors tend to go closed loop a little faster than cars with wideband sensors (which are always heated as well). There was actually a good discussion about this at the recent Consolidated Research Council conference.

Much of the time, the limiting factor in keeping a vehicle from going closed loop right after startup is not rather or not the engine is ready to run at stoich, but waiting on the sensors for reliable measurements.

In an unheated UEGO sensor, the system can't go closed loop until exhaust gas heats the zirconia ceramic to the point that a reaction can occur.

A heated sensor is faster (and generally heated so that the vehicle can get closed loop for emissions purposes faster), but there are still some undesired delays. You can't pre-heat the sensor for startup, because unburnt fuel or condensation would shock cool the ceramic and crack it.

A wideband takes longer to bring up because of the way UEGO sensors work. Stoich is a reversal in chemistry, and effectively correct as long as a reaction is occuring. But the curve off lambda 1.0 with a wideband sensor is complicated, and only 'calibrated' at a specific temp. So instead of just heating above the reaction threshold, a wideband is generally heated more, up to about 750 degrees C, and held there before readings are reliable.

You ALWAYs want to measure lambda pre-CAT. The sensors don't really measure AFR, but equivilency ratio (which is inverted to give lambda). Basically O2 is added or removed to the test chamber until stoich is reached. Since CAT is supposed to be removing hydrocarbons, the post cat sensors are there to see rather or not there is a proper shift from the real (pre-cat) equivelency ratio measurements.

When you get a 'cat efficiency' DTC it generally means that one of the sensors has gone bad, or the shift between pre and post CAT is below expected.

-jjf

Sorry guys, I didn't get a chance to as it was pouring rain and I don't have a garage or carport.:mad:

I'll try again this evening, but the weather is supposed to be the same.

JeepNmpg2 -

No problem. Don't get all wet over it, ;) .

CarloSW2

jfitzpat -

Yikes, that's egg-zactly what I am doing here :

http://ecomodder.com/forum/showthrea...2-a-10921.html

From what you just wrote, I should expect my heated 02 sensor to fail early.

I'm already committed, so I am going to keep using it as intented and see how long it lasts (aka a tootsie roll pop). Another sacrifice in the name of science!

CarloSW2

EQ ratio is a command NOT a measurment
 

...."You ALWAYs want to measure lambda pre-CAT.
The sensors don't really measure AFR, but equivalency ratio

(which is inverted to give lambda). Basically O2 is added or removed to the test chamber until stoich is reached. Since CAT is supposed to be removing hydrocarbons, the post cat sensors are there to see rather or not there is a proper shift from the real (pre-cat) equivelency ratio measurements.

When you get a 'cat efficiency' DTC it generally means that one of the sensors has gone bad, or the shift between pre and post CAT is below expected.
"....

The sensors don't really measure AFR, but equivalency ratio
the above statement is not really true
AFR sensors do measure AFR and
EQ ratio is a command NOT a measurement

in the real world
for actual cars driven on the road -
the ECM does not add or remove 02
the ECM changes the amount of fuel from a base value depending on inputs from various sensors
the amount of change is represented by fuel trim values
short term trim and long term trim on most cars
not all cars

when you get a cat efficiency DTC it almost always means bad cat
because
the cat test WILL NEVER RUN if there is a problem with the 02 or AFR sensors
the 02 or AFR sensor testing must be complete
and it must pass before cat testing will be enabled and
if a 02 or AFR sensor should set a DTC , cat testing will be disabled until the DTC has been cleared
and
then
the 02 or AFR sensor testing will have to run to completion and pass in order to enable cat testing

which would be the reason we save the last run mode 6 test for the cat
prior to clearing DTCs , so we have an idea if the cat will fail when testing is re enabled

if you have a cat efficiency DTC and no other DTC and
all mode 6 and mode 5 tests (if present) have passed
except the cat tests
the cat is bad -

a 2000 jeep has 02 sensors , plain jane bang bang sensors

front 02 heater gets powered up on start not preheated
 

mwebb -

Nope. I *implemented* it so that it's on when the key is turned to the on position. My goal was to pre-heat the 02 sensor before starting the car. I know it's heating up because I have a digital AFR gauge that I watch "go lean" as it heats up.

CarloSW2

Interesting read... I've been pondering URDUSA.com's MAF Calibrator and AFR Calibrator for my 2TR Tacoma.. along with AFR Gauge.. not so much as to juice up the numbers for racing, but to tweak for economy as well. Anyone else doing the same?

4 wires each
 

Ok, like the title says, there are two O2 sensors; one post exhaust manifold, one post catalytic converter and they each have four wires. I discovered this while under my Jeep changing the differential gear oil front and back for some royal purple synthetic 75-90 (got it half off it's normally ridiculous price of 18.99) and my transmission oil and filter (also went to synthetic, but not RP). Hopefully over my next few fuel logs there is some improvement. Can't be too much worse without any towing and running the vehicle for diagnistics for a little while :D

JeepNmpg2 -

Cool. Four wires says (to me) that you have a heated sensor. I call that a superior setup. Unlike my home-made version, your ECU/PCM *knows* it's heated, hence the 30 second transition to closed-loop.

CarloSW2

"Nope. I *implemented* it so that it's on when the key is turned to the on position. My goal was to pre-heat the 02 sensor before starting the car. I know it's heating up because I have a digital AFR gauge that I watch "go lean" as it heats up "....

ok
understand that with a heated 02 sensor or AFR ,
even in very cold ambient temperatures
(i have many many graphs which prove that on various makes and models )
most systems will get to closed loop in 1 to 2 minutes anyway so preheating the heater gains little ,
and if it were or is possible to wipe out the thimble because of temperature shock due to preheating .....

you could always reconfigure your modification such that it powers up when the key is in the RUN position .
and if you choose later to preheat , turn key to run for a minute prior to start .
having said that engineers position the 02 / AFR sensor to minimize the possibility of thermal shock and

and
you should not use an 02 sensor from a system with
an ECM CONTROLLED Heater on time , like for instance from a
2001 VW passat with ATQ engine or a BMW from the same era
because if one of those 02 heaters is run at 100% on , it will have a much shorter life than if it were installed in the correct type of system

a heated 02 sensor from say a 1997 chevy cavalier with a 2.2 IS designed to have the 02 heater powered up with the key in run and would be a better choice
for your particular application
imho
==========================
a digital AFR "gauge" connected to a system with heated 02 sensor
can show you only 1 thing
stoich or lambda or 14.7 to 1
OR unknown amount leaner than stoich
OR unknown amount richer than stoich
if it shows anything else it is showing blarney as 02 sensors CAN NOT measure any other condition

because 02 sensors only show stoich , if they are cycling , the system is at stoich , if the 02 sensors are not cycling , the system will set a DTC
if there is no DTC related to 02 sensors , the system is at stoich
so
on systems with 02 sensors ;
those "AFR Gauges" are as useless as mudflaps on a sledge hammer.
fact .

mwebb -

The digital AFR proves what I want to know. It shows the "cold 02 sensor" go from the 0.5 signal from the ECU/PCM to a lean condition as it warms up. Going lean with the engine off is the proof I need.

I got advice from a dude that works for NGK(NTK?) :

Using heated 02 sensor in place of non-heated 02 sensor? - SaturnFans Forums

Start reading from post #23 and you'll hear what he has to say. His handle is "NGKTECH". He has run my setup for a couple of years without problems, and others have done the same. That *doesn't* document miles, but he appears to come from the harsher climate of Michigan.

Like I said, I'll take the hit if it doesn't last too long.

CarloSW2

proof that the atmosphere is leaner than lambda
 

what is it , that you think you are proving ?
my statement below your quote is correct
so
you are showing that the ratio of the mass of combustibles to mass of air in atmospheric ambient air ...
is LESS than 1 to 14.7 .

anyone can tell you that , with out pre heating their 02 sensor .



a digital AFR "gauge" connected to a system with heated 02 sensor
can show you only 1 thing
stoich or lambda or 14.7 to 1
OR unknown amount leaner than stoich
OR unknown amount richer than stoich
if it shows anything else it is showing blarney as 02 sensors CAN NOT measure any other condition

because 02 sensors only show stoich , if they are cycling , the system is at stoich , if the 02 sensors are not cycling , the system will set a DTC
if there is no DTC related to 02 sensors , the system is at stoich
so
on systems with 02 sensors ;
those "AFR Gauges" are as useless as mudflaps on a sledge hammer.
fact .

Awesome, thanks for the link :thumbup: I just installed a potentiometer in parallel with my coolant temp sensor, with the goal of reduced cold startup enrichment. It works great, except that the idle bounces pretty hard when it first goes into closed-loop, so I'm thinking my single-wire unheated O2 sensor isn't warming up quickly enough.

I just ordered a heated O2 sensor, can't wait to get this in the car and see what happens. Fighting the winter blues...