Catalytic converters removed?

[TODD L GRIFFITH]

Hey DanHammer, Like that yellow coupe with those rims

 

[DanHammer]

Hey thanks Todd ... I find these Z06 rims to be the best not only in looks and performance but in strenght and quality.

 

[Mike Mercury]

The BAD side to simulators, is that this will throw off your fuel trim calculations.

the rear O2's are not used for AFR adjustment... only the front 2 are. How do Sims (for the rear O2's) "throw off your fuel trim calculations" ???

 

[Terry Holtz]

>>>>>>the rear O2's are not used for AFR adjustment... only the front 2 are. How do Sims (for the rear O2's) "throw off your fuel trim calculations" ???<<<<

I am also curious to see this resolved. Am I right in that the front O2 sensors are placed before the catalytic converters??? And if Mike Mercury is correct, then the cats CAN be removed in non-emission states w/o throwing codes so long as simulators are in place????

Let's resolve this debate because alot of cheap horse power is waiting for us if the converters can be safely removed. Thanks.

 

[TODD L GRIFFITH]

The O2 Simulators transpond a fixed voltage value of .450mv. back to the PCM. This is a false reading based on a perfect 14.7:1 AFR. (although not the actual case at all) The actual reading could be .920mv or more being quite fuel rich. The need for tuning is important to avoid detonation and possibly damaging a piston running lean. A good programmer, or LS1edit with diagnostic capability will display your short and long term fuel trims based on what your PCM thinks they are. The chance of a code being thrown with O2 simulators is decreased, because the PCM thinks everything is hunky dory....................:L

 

[TODD L GRIFFITH]

Let's resolve this debate because alot of cheap horse power is waiting for us if the converters can be safely removed. Thanks.

I've seen quite a few threads where people have removed the cats, and were disappointed that they picked up 5hp, I assume at the rear wheels. Not bad, but alot of effort where long tube headers, high flow cats and an x-pipe is where alot more horses are unleashed.

 

[Terry Holtz]

Hib posted this on another thread and since it applies, I quote it here:

"The oxygen sensors which are behind the cats have no effect on the engine controls setting of fuel flow or any other function. The sole pupose of the rear sesors is cat monitering. This was one of the many functions mandated by "OBD2" which was part of the second Clean Air Act and was required (with very few exceptions) on all light-duty vehicles sold in MY96 or later. How the rear O2Ses work is simple. When the signal from the rear sensor(s) starts to mimic the signals from the front sensor(s), the engine computer assumes the cat(s) have failed and turns on the service engine light.

"O2" simulaters are used by those who want to remove the cats but not have the engine controller blow codes all the time. The simulators give the ECM the signals it expects from the rear sensors even thought the cats aren't there."

Thanks for all of the replies. Terry

 

[TODD L GRIFFITH]

If you read my post the PCM thinks everything is hunky dory, because it is getting a false reading from the rear O2's. It does think the cats are there because of the .450mv signal. You just need to keep your fuel trims slightly negative, but the need for a programmer, or LS1edit to tune your engine to keep it that way is important.
http://ls1tech.com/forums/showthread.php?t=121129&highlight=removed+catalytic+converters

Here is a link to LS1tech.com. This will show what I mean about dyno results.

 

[Mike Mercury]

no, nO, NO !!!

Some of you are either:

a. confusing the front sensor pair with the rear pair, or
b. guessing, but not labeling your response as a "guess".

On the C5, only the front 2 sensors are used in AFR determination and adjustment.

The rear pair of sensors are there to give a go/no-go signal to the PCM as to whether the Main Cats are working properly. All one needs do to for the rears is to simulate a voltage that falls within the "go" region. It doesn't matter where (within the "go" voltage range) the sims fall; as data for AFR determination and adjustment is not collected from the rear pair of O2 sensors.
"anywhere" in the GO voltage range means "handsoff, no throwing error codes, and not invoking the limp-mode".

When the rear sensors signal a "no-go" condition, you simply get a CE light that says get-serviced. I have read (but unable to verify) that driving too long with a rear sensor reported failure may result in inacting the limp mode.

Sims fool the PCM into thinking the cats are lit and working.

Now, after all that I've stated... I never suggest the removing of the main cats (unless your C5 is strictly race driven and trailered everywhere). There's little to gain on a mostly stock motor; which doesn't seem to outweigh the rancid smell you have to put up with after main cat removal.

I would suggest going to high-flow cats, like the Random Tech offerings.

 

[Mike Mercury]

Some of you are either:

a. confusing the front sensor pair with the rear pair, or
b. guessing, but not labeling your response as a "guess".

and :

c. Some of you are fast typists, and had the answer posted before i got everything typed !!!!



the best thing for all of us here is to label your answers as either:

* prove-able fact.
* good judgement derived from experience... but not specifically with this exact subject/system.
* common sense that should be correct... but then, may not be either .
* or an outright "guess".

Terry Holtz had the answer, but if he didn't speak out, many here would now be using incorrect info.

:cheers:

 

[TODD L GRIFFITH]

I've already told Terry to go with long tube headers and high flow cats instead. I had O2 simulators in my old 99FRC, after I added long tube headers and high flow cats, I was getting codes. If you check the voltages from the simulators they are in fact .450mv regardless of throttle position, and do emmulate the cats being there. Yes, the front O2's provide feedback to the PCM to determine A/F mixture based on the MAF signal to adjust fuel injector pulsewidth. I'm trying to get Terry interested in a programmer, or software, so he can monitor his short and long term fuel trims, to see if he is rich, or lean after removing his cats, and installing simulators. Then he can advance his timing if needed, and even get more fuel during power enrichment if needed. The original question was about removing the cats, and I recommended simulators and tuning, but didn't think the hp gain was worth the trouble. There were also concerns about getting the car to also pass inspection.

 

[TODD L GRIFFITH]

Terry's post earlier.

Hib posted this on another thread and since it applies, I quote it here:

"The oxygen sensors which are behind the cats have no effect on the engine controls setting of fuel flow or any other function. The sole pupose of the rear sesors is cat monitering. This was one of the many functions mandated by "OBD2" which was part of the second Clean Air Act and was required (with very few exceptions) on all light-duty vehicles sold in MY96 or later. How the rear O2Ses work is simple. When the signal from the rear sensor(s) starts to mimic the signals from the front sensor(s), the engine computer assumes the cat(s) have failed and turns on the service engine light.

"O2" simulaters are used by those who want to remove the cats but not have the engine controller blow codes all the time. The simulators give the ECM the signals it expects from the rear sensors even thought the cats aren't there."

Thanks for all of the replies. Terry

My post #5

Yes, the O2 simulators would trick the PCM into thinking that the cats were still installed by producing a .450mv signal back to the computer. The simulators are to go in place of the rear O2 sensors behind the cats. The simulators can be purchased through Mid America for about $150.00. The link to the online catalog is www.madirect.com .

 

[Mike Mercury]

The BAD side to simulators, is that this will throw off your fuel trim calculations.

since this is quite incorrect; I wonder if there is a way for a forum moderator to edit that post where this claim was made. It'd ba a shame for someone (months from now) to find this tread via a "search" and come away with the wrong info.

long tube headers, high flow cats and an x-pipe is where alot more horses are unleashed.

I gotta agree with that. :yesnod:

 

[TODD L GRIFFITH]

Found this interesting tidbit.

http://www.ecutek.com/tuning/diagnostics/

A/F Correction #3
Short term correction percentage applied to fuelling based on the output of the rear O2 sensor. This sensor is after any catalytic converters and helps to fine tune the fuel mixture to minimise emissions.

A/F Learning #1
Long term correction percentage applied to fuelling based on feedback from front and rear sensors.

Front & Rear O2 Sensors
These parameters report the output voltage of the O2 sensors. Early vehicles tend to have a single 'Front O2 Sensor', whereas newer vehicles have both a 'Front A/F Sensor' and a 'Rear O2 Sensor'. These sensors do not report an accurate air/fuel ratio, but instead provide a rich/lean signal to the ECU. Their output voltages switches sharply as the AFR crosses the stoichiometric ratio. Values of approx 0 to 0.9 Volts are normal. 0 being lean, 0.9 being very rich. The sensor voltage will oscillate between these extremes when under closed loop control. Under high loads, the voltage should never drop below 0.7 Volts. If it does, this means that the fuel mixture is too lean when on boost. Quite possibly there is a fault with the air flow sensor.

This says that the rear O2 sensors do provide the PCM with info. so that your STFT's and LTFT's will be thrown off with simulators. This makes c4c5specialist correct.

 

[Mike Mercury]

This says that the rear O2 sensors do provide the PCM with info. so that your STFT's and LTFT's will be thrown off with simulators.

only if the car is a Subaru. From that text:

"This page details some of the more important diagnostic data that may be retrieved from Subaru vehicles via DeltaDash or the Subaru 'Select Monitor'"

I thought we were talking about the LS1 C5 setup ???

Hib Haverson's text is strictly dealing with the unique LS1 system.

 

[TODD L GRIFFITH]

Here is the point I'm making. The PCM compares the front O2 voltage to the rear O2 voltage to measure catalytic efficiency. Simulators have a "fixed" resistence that always puts out a "fixed" .450mv signal when voltage is applied. The PCM is trying to establish STFT's and LTFT's, but the only thing the PCM can do is look at the delta of the voltages and compare the readings to a table of fixed fuel management values in a given cell, and give it it's best shot. This would be a different table of values in a different cell, if both front and rear sensors were hunting between .100mv to .900mv., thus effecting STFT's and LTFT's based on catalytic efficiency. I think c4c5specialist is technically correct, not flat out wrong. Tuning to offset the +/-25% disparity in other than normal voltage readings between the front and rear O2's would be needed, especially if you are trying to make power and get fuel. The PCM will try to lean the mixture during good emissions. This is what you don't want based on the fixed .450mv signal from the simulators.

 

[Mike Mercury]

Tuning to offset the +/-25% disparity in other than normal voltage readings between the front and rear O2's would be needed, especially if you are trying to make power and get fuel. The PCM will try to lean the mixture during good emissions. This is what you don't want based on the fixed .450mv signal from the simulators.

yep; the reason to reprog is like what you stated - except it's more to keep from invoking the limp mode- due to the disparity between front/rear as you described. The same can be accomplished my maintaining a rear sim voltage that is always on the good side of system normalcy.

And of course this all gets thrown in the trash can when going WOT - when the PCM is no longer in the closed-loop mode and ignores (to the most part) the oxygen sensors all together.

-----------------------------------------------------------------------

"When going to WOT or Power Enrichment Mode. The PCM does several things.


It no longer is concerned with maintaining economical or environmental operations. It freezes the fuel trim adjustments, stops monitoring the O2 sensors, and looks briefly where it was at in “closed loop mode”. It then starts to rely almost exclusively on the MAF sensor input for proper a/f adjustment."