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Thread: Failed Smog - need advice

  1. #1
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    Failed Smog - need advice

    Today I failed the CA Smog test. My car is a 1995 325 convertible with 130,000 miles on it. It currently runs without any problems. However my daily driver is a Harley and for the last five years or so I have only put about 1000-1250 miles per year on the car. It lives in the garage waiting for a nice day out at the weekend. The result of this is that maintenance stuff like oil changes is recent in terms of mileage but may still have been done longer ago than most people do it. It had (stock) plugs 30,000 miles ago and the Oxygen sensor was replaced once but not by me. It was done 50,000 miles ago. I don't think it has ever had a new cat.

    On the advice of the smog test shop I go to, I usually run a tank of gas with a bottle of ""Guaranteed to Pass"" in it before refilling the tank and taking the test. Doing this I passed first time two years ago although it was fairly close. Here are the numbers for today though. I'd be grateful for any advice. And if it helps I can post the numbers for two years ago and answer any questions.

    %C02 %02 HC (PPM) CO (%) NO (PPM)
    Test RPM MEAS MEAS MAX AVE MEAS MAX AVE MEAS MAX AVE MEAS Results
    15 mph 1266 14.6 0.5 59 29 231 0.34 0.08 0.46 486 131 1138 Fail
    25 mph 1380 15.3 0.0 35 17 85 0.33 0.06 0.11 502 94 163 Fail

  2. #2
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    Your going to have to drive the car more and harder, meaning higher rpm. Your injectors are probably gummed up and leaking , so it might take 3 tanks of gas with cleaner. I would replace the pre cat sensor, it's due. You should probably get a new set of coils, ebay has a full set for around $70. Don't do your cat, it's probably fine, it can regenerate once the rest of the system cleans up.

    - - - Updated - - -

    https://www.ebay.com/itm/Ignition-Co...e/130988601979
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  3. #3
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    Thanks, Eric. What is a pre-cat sensor? Remember my car is 1995 i.e. OBD I.

  4. #4
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    Referring to the oxygen sensor, modern cars have one before and after the oxygen sensor. If you had both, the one before the cat is always more important. Shop around for a good price, Amazon, Rockauto. NGK/Bosch/NTK/Denso all good brands.

    - - - Updated - - -

    Apparently the manual trans and automatic trans have different parts, just different length cables. You can get 5% off Rockauto if you go to Retailmenot.com for a code.
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  5. #5
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    I failed smog again this week with almost exactly the same numbers as I posted above. But I just remembered that I had one of the Peake tools for reading trouble codes. When I read them, it turns out that I have two: one is for the knock sensor for cylinders 4-6 and the other is for the Mass Air Flow sensor. Can anyone clue me in on what these could indicate in terms of my bad smog test readings? And what I can do about it? I bought a can of MAF cleaner and that will be my first step.
    Last edited by slamtry; 04-19-2019 at 11:09 PM.

  6. #6
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    What have you done to the car since the first test?
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  7. #7
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    Changed plugs, oil and oil filter.

  8. #8
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    Post the whole report with the proper lines redacted so we don't have to guess about what else is wrong.

    Did you take it to the same station for smog and what gear did they use to run the 15mph test.
    That original test looks odd considering a possible overly rich mixture AND the high NOx at the low speed. Doesn't make good sense.
    However, a good knock sensor would pull the timing back during the low speed/high load run which would also lower the NOx.
    The readings don't really point toward a MAF issue but regardless, you're not passing with any codes present.
    Last edited by tjm3; 04-20-2019 at 10:48 AM.
    See ya later,

    tony
    '98 M3, '92 Dinan3, '05 R1100S BCR, '07 R1200S, Aprilia T

  9. #9
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    Run a bottle of CRC GTP and change the oxygen sensor.
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  10. #10
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    First, check all your vacuum hoses. I would put a new o2 sensor, new cam and crank sensor, new maf, and new knock sensors. That is a basic sensor maintenance. The knock sensors usually last but they do go from time to time. The other sensors mentioned will make your car run like new when they are all replaced together, assuming there are no mechanical issues. The other possibility is an old/worn catalytic converter.

  11. #11
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    The latest test results are below.These are a month after the ones I posted above and in the interim I changed plugs and oil. I have also run through a tank of gas with a bottle of "Guaranteed to Pass" in it. I thought the numbers would get better but they are marginally worse.

    %C02 %02 HC (PPM) CO (%) NO (PPM)
    Test RPM MEAS MEAS MAX AVE MEAS MAX AVE MEAS MAX AVE MEAS Results
    15 mph 1890 14.5 0.5 85 39 242 0.50 0.07 0.53 695 164 1280 Fail
    25 mph 2000 15.2 0.0 50 23 96 0.47 0.06 0.17 717 152 241 Fail

  12. #12
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    I took out the MAF sensor and cleaned it yesterday. Maybe that will help. Never done it before.

  13. #13
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    It won't. Only if you have an oiled air filter (they suck).
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  14. #14
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    We had an e36 that didn't get driven very much put new plugs in it and super gas in it, drove it many time, a lot and finally the thing pasted. The cats need to be good and hot, they won't get hot enough just idling you need a freeway drive i think we drove in in 3 instead of drive to keep the rpm's up. Plus the more it's driven if there is stuff on the cats it will burn off

  15. #15
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    Quote Originally Posted by jclausen View Post
    We had an e36 that didn't get driven very much put new plugs in it and super gas in it, drove it many time, a lot and finally the thing pasted. The cats need to be good and hot, they won't get hot enough just idling you need a freeway drive i think we drove in in 3 instead of drive to keep the rpm's up. Plus the more it's driven if there is stuff on the cats it will burn off
    Absolutely correct. If the car is not driven hard often and only used for short trips the catalytic converter can become coked with un-burnt deposits. Then when you smog the vehicle, these deposits are being blown out the exhaust and in this scenario the buildup would be adding to your emissions. You could try a hard two hour drive to get the cat real hot before smog, but this may only make your numbers worse. I managed to get my car to pass smog with a new catalytic converter, it was right on the edge of passing, the new cat did it. I used a magnaflow ca legal cat welded in to a 49 state (50 now bitches) legal exhaust system.

  16. #16
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    Your car is not running correct. A CAT can allow you to pass for now but it is not a fix and may end up failing in 2 years again.

    At 25 MPH your HC and NOX get better. But HC is always high. Why is the O2 high sb 0.
    I think you may have a mis fire at low speeds and it is better by 25 mph.

    Are the CATS hot when you test? Was there oil on the plugs when you swapped them? Did you use reg copper core plugs? Were any more carbon coated than the others? Are the coils ok?
    The crankcase vent hose can crack or O ring leak at the connector especially on the 95 obd i cars just as bad as the Valve cover.
    Attached Images Attached Images
    Last edited by gc325is; 04-22-2019 at 11:57 PM.

  17. #17
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    Great news. It just passed. Here's the tale. I finally took it to a new and much more competent place. The first guy where it failed (first test, whose numbers are posted at the top of the thread) ran the test as though it were a four cylinder car, which did not suggest any great expertise. The second (second set of numbers posted above) seemed to think it was OBD2. He didn't seem really sure about the visual stuff and had to keep asking his son how to take stuff off. He told me the day before he was sure it would pass and then when it failed said he didn't want to waste my money by doing any work on it since it was an old car, blah, blah, blah. I now think he just wanted to take $70 off me and then get rid of me. Then I found a guy on Yelp with good reviews (A1 Smog, on Van Nuys Blvd, out in the San Fernando Valley) and went there.

    A day previously I had, as mentioned above, taken out and cleaned the MAF because I discovered it had thrown an MAF code. I didn't think it would pass but on the phone, Joe, at A1, had seemed sympathetic and I was also somewhat curious to see if the numbers got any better. Well he had a bunch of clients waiting so I had to hang about for an hour, but he was a very nice guy and anyway I like mechanic's shops. He said that the cat is so far back on these cars that it is hard to get it hot, so he made sure he got it good and hot. First I drove it 25 minutes on the freeway, then he ran it on his dyno machine under load right before doing the test. Anyway, it passed. He suggested I change the O2 sensor and I may get around to doing that if I can borrow the tool to get it off. But woohoo, my car - whose registration and insurance I have been paying pointlessly for the past three months is legally driveable. Of course, as I live in CA and summer's on the way gas prices have already gone well over $4, so I can't actually afford to drive it, but it's nice to know I could. The results are below in case anyone is interested. And I will never be going anywhere but to A1 Smog.


    %C02 %02 HC (PPM) CO (%) NO (PPM)
    Test RPM MEAS MEAS MAX AVE MEAS MAX AVE MEAS MAX AVE MEAS Results
    15 mph 1498 15.8 0.0 85 38 45 0.34 0.07 0.09 695 146 363 Pass
    25 mph 1445 15.9 0.0 37 22 19 0.33 0.06 0.2 502 122 138 Pass

  18. #18
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    Failed Smog - need advice

    You should be able to remove and install O2 Sensor w/combination wrench or an adjustable wrench. Should not be all that tight.


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    Last edited by bluptgm3; 05-04-2019 at 03:01 AM.

  19. #19
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    Quote Originally Posted by slamtry View Post
    But woohoo, my car - whose registration and insurance I have been paying pointlessly for the past three months is legally driveable. Of course, as I live in CA and summer's on the way gas prices have already gone well over $4, so I can't actually afford to drive it, but it's nice to know I could.
    Lol, I feel this. Also have smog, registration past due but have been too busy paying to get the damned thing together to smog. I need an alignment first ffs. They need to change the smog laws, this shit is getting ridiculous. How about we just pull petrol and put it all on E85 and remove smog laws all together? Seems like a good deal for everyone.

  20. #20
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    I shall be using this info for myself too.....if you need an o2 sensor wrench I have one you could probably borrow or something

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