downstream o2 and what it does - Page 2

-Alero- · 06-04-2009, 09:59 AM

Quote:

Originally Posted by lvemy3100

All of this discussion is making me lol

fact is on these cars the 2nd (after cat) o2 sensor does NOTHING other than monitor the exhaust gasses after the cat to let the PCM how the cat is working by comparing readings with the primary o2 sensor.

deleting the rear o2 sensor with a cat still installed will only set off the code in the PCM to let you know its not operating. if you change the DTC table properly the code wont throw but you wont have any kind of waring to let you know if your cat isnt working properly. this is not an issue if you also delete the cat but considering there is little to no HP to be gained from doing IMO its best to just run a cat and 2nd o2 sensor.

the primary o2 sensor is the ONLY o2 sensor that has anything to do with how the PCM calculates fueling needs...

having a code for a bad cat will not change how the car runs but the bad cat itself will.

oh trust me i dont plan on deleting the code i dont have a problem with keeping the cat on, in no way shape or form am i trying to do that, i removed my cat a few years ago to see what it was like, ended up putting back on within a week.

i removed my cat again to prove to a local dealer my cat had nothing to do with my idling and they simply just said "its because you need an OEM cat".....Tons of facpalming that day

-Alero- · 06-04-2009, 10:01 AM

Quote:

Originally Posted by bdyman

my car has the same problem same code, i have the ecotec, now my mechanic told me it could be a vacum leak,or a stuck fuel injector, iam going to him when the weather clears up here and when he fixes the problem, i will report back in here to give you a answer

yeah vacuum leak seems like it could be possible with me......its just playing the game of diagnosis is what the dealer doesnt want to do....its so lame...

my car is 90% stock now, stock airbox, stock pcm coils etc etc. all it has is the aftermarket exhaust, crank pulley and lowered......i only turned it to stock for the dealers to not label me as a "racer"

bdyman · 06-04-2009, 10:01 AM

according to my mechanic, if the cat is plugged or defective then yes replace i think we all know that one , but he said this problem is fixed without replacing the cat, as soon as mine is fixed i will tell ya what it is

-Alero- · 06-04-2009, 10:03 AM

Quote:

Originally Posted by bdyman

according to my mechanic, if the cat is plugged or defective then yes replace, but he said this problem is fixed without replacing the cat, as soon as mine is fixed i will tell ya what it is

ok that works despite our different engines i would still like to know. im going to another dealer today with alot on my mind, ill be sure to post on what they say.....dreading having this arguement with a biased service writer.... sigh

lvemy3100 · 06-04-2009, 10:04 AM

have someone hook up a scantool to your car and check individual cyl misfires and other parameters and see if you cant find your idle issue that way..

bdyman · 06-04-2009, 10:05 AM

Quote:

Originally Posted by -Alero-

yeah vacuum leak seems like it could be possible with me......its just playing the game of diagnosis is what the dealer doesnt want to do....its so lame...

my car is 90% stock now, stock airbox, stock pcm coils etc etc. all it has is the aftermarket exhaust, crank pulley and lowered......i only turned it to stock for the dealers to not label me as a "racer"

dealership tech are parts changers ,plug in the scan tool ohh its this part, unless your willing to pay out the ass for their work your alomost better off going to a ma and pop shop thats where i go hes updated on the newer cars gos to the gm training

like next week on a nice sunny day iam going to him as soon as iam back i will tell ya

bdyman · 06-04-2009, 10:06 AM

Quote:

Originally Posted by lvemy3100

have someone hook up a scantool to your car and check individual cyl misfires and other parameters and see if you cant find your idle issue that way..

yes like check fule injectors pulse, and some other shit he was going to do, check for vacum leaks, btw arent you a mechanic??

lvemy3100 · 06-04-2009, 10:10 AM

Quote:

Originally Posted by bdyman

yes like check fule injectors pulse, and some other shit he was going to do, check for vacum leaks, btw arent you a mechanic??

indeed I am.. and happy to help out almost anyone on this forum if they can make it to Round Lake, IL

-Alero- · 06-04-2009, 10:15 AM

i would seriously kill for MPracing or WOT to look at my car. but yeah its just, i think we have lazy techs here or something because none of them want to use thier scan tool.... they just pull the code and go from there....so lame

lvemy3100 · 06-04-2009, 10:25 AM

Quote:

Originally Posted by -Alero-

i would seriously kill for MPracing or WOT to look at my car. but yeah its just, i think we have lazy techs here or something because none of them want to use thier scan tool.... they just pull the code and go from there....so lame

Idk where you are located but if you can make it out here I am happy to check it out..

kinda weird that they dont wanna do any more than pull the code since out here the first thing they (dealer techs) try to do is tell people that they need to hook up the scan tool and then try to charge an minimum of an hr labor @$120/hr that no one can afford anymore. only reason i know is cause I end up with alot of them coming to me for the free 5min scans I offer (if they are lucky enough to hear about me before being ripped off)

[ion] C2 · 06-04-2009, 11:37 AM

Long term fuel trims are not what the downstream O2 is for. The computer starts to make long term fuel trims based on the sheer amount of the same values for the short term fuel trims. If there's a lot of -5% going on all the time, that's going to be logged as long term eventually since it's obviously not a short term fueling change.

Rear O2 is solely for catalyst efficiency monitoring and has nothing to do with fuel control in closed loop operation, as Cliff8928's post clarified.

bdyman · 06-04-2009, 01:03 PM

Quote:

Originally Posted by lvemy3100

indeed I am.. and happy to help out almost anyone on this forum if they can make it to Round Lake, IL

dude i would like to but thats just way to far for me to travel, you could come to me if ya want........

Cliff8928 · 06-04-2009, 01:17 PM

Quote:

Originally Posted by -Alero-

hmm nice post cliff but where di you get it from?

also this ite explains alot http://www.aa1car.com/library/p0420_dtc.htm

factory service info.

Raziel · 06-04-2009, 03:24 PM

I don't know if it would make much sense, but have you checked your IAC modual or motor, I had a prob with my Alero with starting and idling rough and that is what it turned out to be. Maybe try that and see what happens.

Raz

-Alero- · 06-04-2009, 07:18 PM

idle air control valve gets cleaned regularly, havent changed it but seems to be in working order....

got back from dealer, no help, they said all my sensors read just find and that i need a new catalytic converter.....just like all the others

they also said i had nothing wrong with my idle, and said they have no reason to perform diagnosis on an engine they believe nothing is wrong.

i told them over and over how little influence the cat has on my idle and i can come in with a hollow cat no cat, disabled downstream O2 sim, and it will still run the same.

they said it needs a OEM cat and nothing in the world is better than a OEM cat. i then asked why would companies produce OBDII spec 50 state legal EPA approved converters, and he said they are no where near oem spec.

i then got in a very very heated arguement with the service writer/manager who took a ride with me, and the last thing i said was "im not going to play the game of buying your 900$ cat and then come in a week later with the same code and the same problem" he then said "well then this game is over" and got out.....

end of story, back to square one......no idea what to do.... it idles like garbage and im told it idles flawlessly hwen you stare at the engine it bucks back in forth like its having the time of its life....

FML

jackal2000 · 06-04-2009, 07:40 PM

have you checked the motor mounts?

-Alero- · 06-04-2009, 08:02 PM

have not looked at the very rear one near firewall. the side one near pullies seems fine, and the front tranny mount seems just fine.

pushing weight in different directions on the engine while its off, seems fairly solid....

but if i took this thing to ASS and let any one of you sit in it i guarentee every single one of you would say "whats wrong with your idle?".......

sigh might cut my losses i dunno.....dont have the money to replace the car though so im basically in a sweet spot

[ion] C2 · 06-04-2009, 08:23 PM

take it to ass dude it's easier to diagnose a problem when you have 24 alero guys on site

-Alero- · 06-04-2009, 08:27 PM

the car is basically stock now i dont have much to show anymore...... jackal actually lives relatively close he has a program ive been wanting to use for a while....

[ion] C2 · 06-04-2009, 09:01 PM

not that excuse again. zoL's coming from massachusetts, so is nate's alero from NH and they're basically stock.

hell 3 california guys are coming, a pretty close to stock, why not come check out everyone's aleros?

guiguilandry with his 3800 s/c swap, custom hood, custom trunk, custom interior
rowdygls with his all around modified car
bdyman's work of art
etc.