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Discussion Starter #1 (Edited)
I attached my smog results from this morning. It was recommended that I replace my O2 sensors, as it failed on 15mph and passed on 25mph the first time, and vice-versa the second time, and so he made that suggestion based on the variation.

I have recently replaced the pre-cat sensors, and will be replacing the post-cat O2 as soon I order/receive them. Possibly clean my MAFs also.

Any other insight that you guys have that I might be forgetting?

Parts changed in the recent past:
Fuel filter
Pre-Cat O2
Spark plugs
Filters
Oil
Exhaust CPS
New MAFs

PS: Car has 71,xxx miles.
 

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Definitely new post cat O2. The zero on the NOx tells me that the posts are saying there is more O2 than there is. Standard way for them to fail. The HC and CO raising together is not a great sign, but does not mean de*ath (can't believe that got censored) either.Could be from a few things. Both could be because of to much exhaust gas being held in the system by the faulty post O2s. But its usually lack of efficiency of cats. High HC is usually oil or most likely poor atomization by the injectors.

Fast fix is injector cleaner double dose for two tanks. No injector cleaner in the tank for the test, instead use "CRC guaranteed to pass" Methyl hydrate if you are real cheap. No 96 in your tank for the test. Low Octane is better than high for the purposes of a emission test.
 

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Fast fix is injector cleaner double dose for two tanks. No injector cleaner in the tank for the test, instead use "CRC guaranteed to pass" Methyl hydrate if you are real cheap.

I have to change this. Bad info I hate when I do that. It appears that this product has changed at least here in Canada. Now as best I can tell it is just a super strong injector cleaner. So strong that it warns you to only use 4 times a year. The parts guy told me the product I used ten years ago was methyl hydrate + additives. It has been band because according to him it was to effective. He said if I had added a gallon to 5 gallons of gas and cut the cats out, you could still pull a pass on HC.

A substitute for that would be a few small bottles of gas line anti freeze. I would just dump methyl hydrate in but god knows it has not been purified for an engine.
 

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Check operating temp via OBC hidden menu, #7. Have seen a lot of thermostats failing around this age/mileage with car running too cold, this would definitely cause higher than normal HC levels due to quenching effect. A quick finger in the tailpipe will help determine this as well, if it comes out oily/greasy/black chances are your stat is bad.

I was also thinking Vanos O-rings/solenoids as well.
 

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Discussion Starter #8
Thanks for the heads up guys. I'm going to recheck everything this weekend. Menu #7 shows correct KTemp at highway cruising speeds, however, I may replace it as PM. I'll update on my smog re-check.
 

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What is correct temp at highway cruising speed?

These cars run at 79C up to about 50F ambient temps, after that they should run at about 83-85 up to about 70F, I have not had my car in warmer weather yet, however, I would expect 90+C temps once you get above 80-85F outside?

Just want to make sure you were not looking at 79C as the proper operating temp, this should be the "minimum" operating temp.
 

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cal

my car is always borderline in the HC tests. my mechanic suggested to run the car hot (get the cats hot - i just take it to a hway) and
go to the smog place asap without turning off your car... straight to the rollers! always worked no problem.
 

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my car is always borderline in the HC tests. my mechanic suggested to run the car hot (get the cats hot - i just take it to a hway) and
go to the smog place asap without turning off your car... straight to the rollers! always worked no problem.
A good old trick, my mate who used to MOT my old car locally used to take it for a blast first and get it all proper hot, once he'd refitted the cat, hten it would pass easily, and then he'd re-fit the de-cat pipe :)
 

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Discussion Starter #13
Thanks for everyones help.

I replaced the Post-Cat O2 sensors after the first initial fail, and I passed last night, well under MAX.

Note: I run Powerchip Header SW, SS header, stock cats, muffler deletes.
 

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Discussion Starter #15
The only difference in my situation between the first test (fail) and the second test (pass) was changing the Post-O2 sensors.
 

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Discussion Starter #16
Definitely new post cat O2. The zero on the NOx tells me that the posts are saying there is more O2 than there is. Standard way for them to fail. The HC and CO raising together is not a great sign, but does not mean de*ath (can't believe that got censored) either.Could be from a few things. Both could be because of to much exhaust gas being held in the system by the faulty post O2s. But its usually lack of efficiency of cats. High HC is usually oil or most likely poor atomization by the injectors.
Thank you for your help!
 
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Sorry to side track you fellas a tad with this small question but I must ask. I just replaced my pre-cat 02 sensors with the OEM Bosch units a few nights ago. Super easy install & made a noticeable improvement in throttle response. Guess she was running a tad rich before. My car is due for a SMOG test next month. Should I replace the post cat 02 senors as well... ?

All this talk about "post" cat sensors has got me thinking & my mind wondering about them...
 

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Thanks for everyones help.

I replaced the Post-Cat O2 sensors after the first initial fail, and I passed last night, well under MAX.

Note: I run Powerchip Header SW, SS header, stock cats, muffler deletes.
Glad to hear this, did you have any codes. soft or otherwise? Very strange
 
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Discussion Starter #19
Sorry to side track you fellas a tad with this small question but I must ask. I just replaced my pre-cat 02 sensors with the OEM Bosch units a few nights ago. Super easy install & made a noticeable improvement in throttle response. Guess she was running a tad rich before. My car is due for a SMOG test next month. Should I replace the post cat 02 senors as well... ?

All this talk about "post" cat sensors has got me thinking & my mind wondering about them...
It's not necessary, but if you are under the car anyways, it's an easy change as you know. It certainly does not hurt, except the wallet.

Glad to hear this, did you have any codes. soft or otherwise? Very strange
Thanks! No codes that we pulled. Based upon assumptive knowledge, changing the thermostat was next on the list if Post-O2 did not work.
 

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Yes, no, maybe, good answer ehh! Don't want anyone to get the wrong idea posts don't do anything to performance except make the car run a little rich when you are cruising down the highway at lower rpms up to 3000, if bad. Its main function is to check air after the reaction in the cat. If there is too much air then the Nox will be high so they ask the DME to get rid of it. This is all done by comparing the wave forms of the sensors. If they are totally done and failed in a none standard way, I have seen some weird drivability issues. Most of the time(when bad) they have the air cut back so far that there is not enough left over to complete the reaction in the cat. Exactly what went on with the OP.
The right answer is to check the emissions from the tail pipe with an exhaust gas analyzer. That will tell you when to change your post cat sensor. You don't have one handy and would have to pay for that service. You would also have a cost for the failed emission test. Bottom line most economical would be replace them at 100,000kms. That works out to about 15 cents per 100km in expense. Since it costs me about $22 in gas to drive that 100km I replace mine, you never know you might actually save that 15 cents in gas.
The life they see after the reaction in the cat is not nearly as harsh as the pre cat, and they last longer. The usual way I do it without any testing is to look at the protective sheath around the wires. If it is worn, has holes and the cloth threads are showing I assume they are original and read the mileage.
 
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