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Thread: Failed smog again but way closer to passing

  1. #1
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    Failed smog again but way closer to passing

    Everything came way down - now only the HCs are giving us issues.

    They start out great 10 to 20 or so - but slowly climb and go up to 250 to 500 then drop back down to 130 or so and then start up again. To pass it needs to stay below 140 parts all the time.

    This is at idle and 2500 in second. Talked to an older Germany "bosch factory" trained mechanic next to the smog place that said fuel pressure every important. I mentioned that my Lambda control valve "I think" or frequency valve buzzes all the time on this car - which he said is not right.

    As I understand the Bosch injection book, it basically says the O2 sensor feeds the computer and then it controls the frequency valve accordingly.

    So either the 02 sensor could be bad, computer could be bad or Frequency valve.

    Anyone have any quick test or ideas for trouble shooting this one?

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  2. #2
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    It is surprising that he said that the frequency valve buzzing all the time is not right, my understanding is that it should be buzzing all the time unless it is running rich.
    I have never heard or seen frequency valve fail, same for the "computer". 02 sensor is short lived and is cheap to replace ($30). If you have not replaced the 02 sensor, I'd do that first. Even though the 02 sensor does not do that much in these cars, bad one could mess everything up.

    After the new 02 sensor I'd try to find a gas analyzer and see what the pre cat numbers are, you may be running lean and it would drive unburned fuel (HC) up.

    Max

  3. #3
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    The FMV should be running quite a bit, bottom line Max other way around--too rich is too much fuel and some goes thru the cat unburned and is detected by the tail pipe sniffer---sounds like you need a new cat--California changes the standards on cats and once they are beyond warranty 5 years/ 50,000 miles-many do fail , a new 3 way-cat will lower CO's, HC's and Nox to pass Smog for another 5 years--3 Tests.

    Randy
    Last edited by 320iAman; 09-12-2018 at 10:00 AM.

  4. #4
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    Thanks for the help Max and Randy!

    Was tinkering with the car yesterday - while it was was running I bumped the engine wire loom at the fuse box the the engine died. Would not restart until I moved it again but moving it again kills it.

    So I have a wiring issue I need to look into, more fun.

    Thing that is confusing is how good the car runs? Use to start right up and great acceleration and runs great down the road, only issue is a little searching for idle speed. You can hear it searching but it is so little it does not show up on the tach, maybe 50 rpm or so.

    - - - Updated - - -

    Quote Originally Posted by 320iAman View Post
    The FMV should be running quite a bit, bottom line Max other way around--too rich is too much fuel and some goes thru the cat unburned and is detected by the tail pipe sniffer---sounds like you need a new cat--California changes the standards on cats and once they are beyond warranty 5 years/ 50,000 miles-many do fail , a new 3 way-cat will lower CO's, HC's and Nox to pass Smog for another 5 years--3 Tests.

    Randy
    Smog guy does not think it is the cat because of the way the HC move around. They start out great then go up and up and then back down to passing to only start over with going up and then back down. He says that if it was the cat it would just be bad go up and stay there.

    I am thinking now I have a wiring issue and a fuel pressure issue - WUR has power to it but not sure about the ground wire.
    Last edited by OLD MAN; 09-12-2018 at 11:04 AM.

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  5. #5
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    There is test only and test and repair shops, never heard of smog going up and down.

    Randy

  6. #6
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    Quote Originally Posted by 320iAman View Post
    There is test only and test and repair shops, never heard of smog going up and down.

    Randy
    I was in the back and saw the read out went up and then back down HC only everything else was great.

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  7. #7
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    Randy, my understanding is that HC is unburned gas, if it's too lean (almost missfire) HC number would go up as well. I have seen it happen on my car, too lean lowered CO but raised HC/Nox.

    Daryl, seeking idle is normal if the K jet is running in closed loop, that's how FV is working. If your CO # is not too high you may want to richen the mixture a little and HC may go down. How is NoX? If it's high then you have high temps in the combustion chamber ( lean or advanced timing).

    By the way, how is the timing? Retarding the timing may help and you can lean it out if needed. If the timing is too advanced, while on the dyno, vacuum advance might overadvance it and cause a miss which would raise HC... Just a thought.

    Max

  8. #8
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    HC and CO is easy to get mixed up when trying to describe.

    CO = Black Soot.

    HC = Raw Fuel.
    ---
    High HC could be from lots of things, some listed it the other thread.

    If it were me, I'd probably first make sure the plugs are gapped within spec. Plain copper or silver plugs too (get new plugs, maybe).

    Daryl, what did you do to get better HC readings this time around?
    Tbd

  9. #9
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    Thanks for all the input guys!

    Robert I -

    Ran two tanks of gas through it with Royal Purple injection cleaner in them
    reset AFR at idle
    checked plugs - which were new to start
    checked timing - which is 25 total advance at 2200 with vacuum attached
    plug wires, cap and rotor are almost new
    new O2 sensor


    I am thinking I have a fuel pressure issue -

    Maybe too low allowing plunger in fuel distributor to move too easy?

    CO and NOX are in the low area of the allowable range, both of which were really high the first time around.

    HC and CO where above 1,500 the first time through.
    Last edited by OLD MAN; 09-13-2018 at 10:56 AM.

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  10. #10
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    Thanks for that info Daryl. It's always good to know the fuel pressures when t-shooting. Hoping your testing reveals something.

    I was also curios of what plugs and gaps you are running. And if the valves are adjusted within spec - a leaky or tight (less than .006") exhaust valve could let some extra HCs out.

    Good luck and hoping you also figure out that wiring issue (may have something to do with the problem, if ignition/fuel related!)
    Tbd

  11. #11
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    Daryl, I'd try retarding timing a little. I think it's too advanced. I believe the spec is 25 deg. at 2200 with the vacuum disconnected, but it depends on the distributor, there were 2 versions. Also, I have learned that older stock motors can no longer run stock setting, may have to do with today's gas or carbon build up...

    Max

  12. #12
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    In Europe with adjustable CO's, these cars 80-83 run from .2 to 1.2% CO's, what most do is too adjust the CO to the lower end,this brings down CO and HC's as this shifts the air fuel ratio to more leaner setting - more air -less fuel ratio, then adjust it back to richer settings once the test is done and past, the motor though when running lean will heat extremely fast so you dont want to leave it there, richer air fuel ratios with higher CO's and HC's actually keep the motor cooler. There is nothing shady about this--you see .2 or leanest settings is acceptable to run in, both from BMW and Regulations, its allowable and has been for over 35 years. The final item here is NOX-- the hotter the motor the higher the NOX- State interpretation so there is a trade off to get Lowest CO,HC's and Nox's.

    Randy
    Last edited by 320iAman; 09-15-2018 at 10:55 AM.

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