O2 simulators? (R.I.P. another catalytic)

[Tommymc]

My CEL went off and is indicating the catalytic is shot in my '96 Legacy wgn. This will be the 3rd or 4th replacement and I think enough is enough. The aftermarket cats don't work at all, and I only get a couple of yrs out of the OEM ones.

Sooooo........I'm looking at DIY alternatives and have a few questions. I thought the first and easiest 'fix' would be the mechanical one using spark plug anti-foulers:http://www.importpassion.com/forums/showthread.php?t=15507

1. Has anybody tried this and is 18mm the correct thread for Subaru?

2. Assuming it works, will the CEL go off after enough cycles or is there another easy way to shut it off?

3. O2 simulators...a bit more expensive. Has anybody had luck with them?

Thanks.

[Gloyale]

Have you tested the O2 sensor? Had it replaced? The sensors fail more often than the Converters.

[WJM]

Do a tailpipe sniffer test. If the values are within range then you have other problems...electrical ones with the sensors.

[Tommymc]

Do a tailpipe sniffer test. If the values are within range then you have other problems...electrical ones with the sensors.

I had the car into a shop that specializes in Subarus. It was their call that the converter is shot. The other times the cat went, the sensors were replaced too. I went through 2 or 3 aftermarket cats (under warranty) and finally had to put in an OEM part before the problem was solved. Two different shops have told me this is a real problem with Subarus. Has nobody else experienced this?

 

Anyway, I picked up a pair of spark plug non-foulers and assembled the 'extender' for the o2 sensor. 18mm is the correct thread. The CEL is still on, so either the fix isn't working ($3.97 down the tube) or I need to reset it. Any suggestions on how to do that without a scanner would be appreciated.

[nipper]

Let me guess, thosae 3 cats all came from the same supplier....

 

who is?

 

 

nipper

[porcupine73]

Does it begin with E and end with N?

[nipper]

Does it begin with E and end with N?

 

Thats what i was thinking.

 

nipper

[WJM]

I had the car into a shop that specializes in Subarus. It was their call that the converter is shot. The other times the cat went, the sensors were replaced too. I went through 2 or 3 aftermarket cats (under warranty) and finally had to put in an OEM part before the problem was solved. Two different shops have told me this is a real problem with Subarus. Has nobody else experienced this?

 

Anyway, I picked up a pair of spark plug non-foulers and assembled the 'extender' for the o2 sensor. 18mm is the correct thread. The CEL is still on, so either the fix isn't working ($3.97 down the tube) or I need to reset it. Any suggestions on how to do that without a scanner would be appreciated.

 

its not a 'problem' but on average an N/A SUBARU will usually eat a set of cats and sensors once every 100k~140k miles. thats the average I've seen. However, I have seen MANY that go well past 200k before needing them. Some have issues before the 8yr/80,000 federal warranty runs out.

 

But in most cases they usually go 100k~140k. thats the average I've seen.

 

Areas with a higher SUBARU population a shop/dealer will see a larger volume of P0420 vehicles. Its not a problem...its just normal wear and tear.

[Tommymc]

Let me guess, thosae 3 cats all came from the same supplier....

 

who is?

 

 

nipper

I really don't know. The shop I went to has specialized in Subarus and Saabs for at least 25 years and is reputable. They were trying to save me money by using aftermarket cats. When the aftermarket cats failed almost immediately, they took them back under warranty and put in a Subaru part. This was in 2003. Two years later, (after ~25k more miles) the engine was replaced, (my daughter didn't notice the car overheating until too late when the water pump failed.) and shortly after that the cat went again. The shop theorized it might have been damaged when the old engine blew. Now here we are after another 25k-30k miles and it's gone again. I've got it in a different shop and they are telling me the same story: "we see it all the time." Subaru is the unofficial 'state car' of VT so they are seeing a large sample. BTW, does that 8yr/80k warranty apply to the replacement cats too, or just new cars?

That's why I'm looking at alternatives....so back to my question about o2 simulators and turning off the CEL. Do any of the simulators get the job done, and is there any way to reset the CEL without a scanner which I don't have? Thanks.

[WJM]

I dont know how that warranty affects cats put on after the original 8/80 has expired.

[Skip]

Hi Tommy

in reference to O2 simulators

I've never heard of one so I can't answer that

 

but I have read about the anti foul adapter trick.

 

To clear the codes the item causing it must be repaired.

 

If as some eluded to the 02 output or it's wiring is faulty

the code will not clear, or will reset it self

as soon as closed loop mode is established

(engine at normal op temp)

 

Battery disconnect used to work on the OBD I

cars but I don't think so on OBD II vehicles.

Plus you then have to deal with readiness monitors...

another topic

 

Go to a large chain auto parts

(i.e. AutoZone or Advanced Auto)

They will scan and clear codes for free.

 

This shop you go to must have a scanner capable also.

 

Hope you get it fixed.

 

Sounds like an 02 problem or something is killing your cats

(too much lead in the gas???, too rich a mix due to tired 02 sensors??)

[WoodsWagon]

Cat's don't just die in 30k miles, they get killed. Something else is wrong. The engine has to be running too rich. What's the MPG like on the car?

 

You put the anti fouler on the O2 sensor after the cat right?

 

Oh, by the way, these aren't O2 simulators. All this does is shroud the O2 from the exhaust gas flow, slowing the readings down and making the computer think that the cat is working.

 

This is an O2 simulator http://www.afterthoughtsauto.com/o2sim.html

[WJM]

Battery disconnect used to work on the OBD I

cars but I don't think so on OBD II vehicles.

 

I've actually had several OBD-1 Imprezas very UNwilling to clear with just a battery disconnect. I had to get out my Select Monitor 1 and clear it. However, on 100% of the OBD2 cars I've dealt with, the battery disconnect has cleared the codes...unless its one of those 'immediately upon fault recognition' codes like a MAF or MAP or something like that.

 

It does reset the I/M tests...but thats another topic entirely.

[WJM]

Cat's don't just die in 30k miles, they get killed. Something else is wrong. The engine has to be running too rich. What's the MPG like on the car?

 

You put the anti fouler on the O2 sensor after the cat right?

 

Oh, by the way, these aren't O2 simulators. All this does is shroud the O2 from the exhaust gas flow, slowing the readings down and making the computer think that the cat is working.

 

This is an O2 simulator http://www.afterthoughtsauto.com/o2sim.html

 

 

From the site:

The PCM does NOT use any data from the secondary O2 sensor for engine management.

 

That is absolute BS when dealing with SUBARU. SUBARU's use the front O2 or AF sensor when doing the primary short term and long term fuel trimming while in closed loop.

 

However, there is this long term and short term '#3' trimming which the ECU uses the rear most O2 sensor for. It uses it as a fail safe to make sure both sensors are seeing the same trimming. If the two readings are out of whack, it sets off codes...as you have a fuel control issue with either the front or rear or both sensor sets.

 

IF that rear O2 sensor is not present or fooled in some way on the 2000+ cars (1999 for Calif. cars) it will severely mess up the long term and short term fueling. It will also severely affect your fuel mileage in negative ways.

[WoodsWagon]

Good info, but this is a 1996 legacy we're talking about. So the rear O2 is there as a catalyst monitor only.

[Skip]

"However, on 100% of the OBD2 cars I've dealt with, the battery disconnect has cleared the codes..."

 

WJM, I thank you kindly sir for the correction and

will use this information in future studies.

 

I use my scanner to clear codes as to not mess with the

readiness monitors.

(or more importantly-> the radio presets - arf arf)

 

Also thanks for the explaination of the 02 sensors operation.

[WJM]

Good info, but this is a 1996 legacy we're talking about. So the rear O2 is there as a catalyst monitor only.

 

It still uses it as a fuel reference. I ran w/out a rear O2 for a month on my 96 Outback and MPG dropped from 30 to 22.

[WoodsWagon]

This is pulled off of EndWrench for the '99+ speed density systems

 

In reference to the rear O2 sensor

When a lean air-fuel mixture is burnt in the engine, oxygen remains in

the exhaust gases even after the catalytic action, and this results in a small

difference in the oxygen concentration. The electromotive force generated

is very small.

The difference in oxygen concentration changes greatly in the vicinity of

the optimum air-fuel ratio (stoichiometric), and the change in electromotive

force is also large at this point. By inputting this information to the ECM,

the air-fuel ratio of the supplied mixture can be determined. Since this

information is collected after the exhaust gases have passed through the catalytic

converter, the effectiveness of the converter can also be determined.

 

Normal O2 sensor boilerplate description, but it seems to say the for the speed density system, it uses the rear sensor as well to determine the fuel air mix.

[WJM]

Speed Density=MAP.

 

Yes, in 1999 calif and 2000+ Fed cars they started using the rear O2 more for fuel trimming.

 

while its affects are not as large on the older cars, they still incorperated it.

 

large meaning that w/out it there on the 2000+ cars, the ECU is just not happy at all.

 

the older ones...it seems to be fine but something is amiss as the MPG drops pretty noticeably.

[subaru360]

For the original poster- Your '96 legacy doesn't use the rear oxygen sensor for anything but catalyst monitoring. If you disconnect the battery for a few hours, or overnight it will clear the code without a scanner. The 2 anti-fouler trick usually does work good on these year cars.

[destey]

Not sure if its been said yet, but a leak in the pipes upstream of the sensors can change the readings.

 

Are the formulas on how the ecu figures fuel trim known outside of subaru engineering?

[WJM]

Not sure if its been said yet, but a leak in the pipes upstream of the sensors can change the readings.

 

Are the formulas on how the ecu figures fuel trim known outside of subaru engineering?

 

Agreed. Check for leaks as well.

 

as for the formulations...no. So far as I know it, Cobb, Ecutek and the opensource community have not gone so far as to decode that part of the ecu and alter it to not use the sensor. Its only the 2000+ ECUs that can be reflashed.

 

Some MY99 ECUs can be, but are finky when reflashed.

[Tommymc]

Well, this is a lot of info to digest!

Originally Posted by 91Loyale

Cat's don't just die in 30k miles, they get killed. Something else is wrong. The engine has to be running too rich. What's the MPG like on the car?

 

You put the anti fouler on the O2 sensor after the cat right?

 

Oh, by the way, these aren't O2 simulators. All this does is shroud the O2 from the exhaust gas flow, slowing the readings down and making the computer think that the cat is working.

Yup, I realize that. I just thought I'd try the cheaper option before springing for a simulator. I haven't checked the MPG recently because this is the car my daughter has at college. When it was the family car, it got around 25 mpg. I have wondered if there was something killing the cats. Wouldn't a rich mixture trip a code on the CEL? If there is something else wrong, I'd prefer to fix it before running through another new cat.

 

So I drove the car today, and the CEL reset itself. Now I'm just confused about whether shrouding the rear O2 sensor will adversely affect the car's performance. I'm hearing yes, no and maybe. Is there any difference between the anti-fouler and using a real O2 simulator in this regard? They are both sending false readings, correct?

 

Should I just keep an eye on the mpg and leave the anti-fouler in.....or deal with the annoying CEL until it's time for an inspection sticker?

[WJM]

Fouler would be better. I've not seen any problems from those used on older and new cars.

[Tommymc]

Ok thanks....I'll leave it in. She's headed back to school tomorrow. It's a 7 hr drive and any loss of mpg should become apparent. Only problem is that then I can't undo it till she comes home for spring break.