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Thread: Well what do ya' know...she passed!

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    Registered User rcb280z's Avatar
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    Default Well what do ya' know...she passed!

    A lot of you know I have been working on my "rich" condition off and on with my 77 280. California has some tough smog laws! So after replacing, rebuilding, testing, cleaning, adjusting, rewiring, searching, trial and error, cursing (lots) she passed. I'm actually looking at the numbers now and have come to the conclusion that I can richen her up a little. The CO and HC readings are very low, too low for the engines sake as far as the CO goes. The smog tech said he has never seen numbers like these on a Z. So that made me feel pretty good. Thought you all would like to know. And thanks to those that offered help and ideas during the past 6 months.
    Last edited by rcb280z; 05-19-2012 at 04:08 PM.

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    Registered User grantf's Avatar
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    Very cool! I sure am glad I do not need to smog my 77 here in Seattle, but if I did it would make me tune up my car more often. Good job.

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    Registered User ZCurves's Avatar
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    That is fantastic! So now that you have tasted victory, perhaps you could list the steps you took to remedy the issue. I am betting there are a bunch of others out there with similar problems. I know I am interested - even though I am in Texas I still would like to have my Z running as clean as possible.
    Congratulations again
    Andrew (ZCurves)
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    Boat Anchor Repairman Captain Obvious's Avatar
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    Congrats! Maybe drive it for a little bit and then pull the plugs to make sure that your aren't too lean?

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    Registered User rcb280z's Avatar
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    Yeah Capt. Obvious, just what I am going to do. After I make a small adjustment to the AFM....to richen just a little. I can tell I am a little lean...the test results prove it also. Andrew, this was definitely a challenge. And one I thought I wouldn't win a few months ago. It was just a matter of understanding what the service manual was saying and I needed you all for that help a few times. Andrew, I will share everything I learned whenever you need it. I'm on this site daily.
    Hey Grantf, YES be very thankful you don't need to smog! Unless you have owned your Z from day one and have performed the maintenance required and didn't have a PO get in there and screw things up then it can be tough. Anyway, now I can install my aluminum radiator and start other projects on my Z. Will post that as well.

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    Registered User beermanpete's Avatar
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    If the HC is low it is not too lean. When it gets too lean the HC will rise even though the CO continues to drop. Keep in mind the smog test is done at idle and light throttle. It can be a bit lean at idle and rich at large throttle openings and still pass the test.

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    Registered User rcb280z's Avatar
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    Actually the smog tests are done on dyno's now in CA. 15 mph and 25 mph tests. I believe they no longer do idle tests. I got to watch the process. The tech walked around to the back of the Z and shook his head. I asked if something was wrong and he said "oh no, thought the probe came out of the exhaust because the numbers are so low"! I'm not so concerned about the HC. CO is 0.01 at 15 mph test and 0.00 at 25 mph test....too lean depending on who you talk to. You are allowed 0.50 CO. HC readings were up there (but still really low for CA standards)) for both 15 and 25 mph test. It's only going to take a very small adjustment of the AFM bypass screw to dial it in where I want it. Just looked at plugs and they show lean as well. The leaner you go the more HC you produce. I am going to a shop here in Ventura to have them test it after I do a small adjustment and will post results. I'm curious just how much the numbers are going to change after my small adjustment.

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    Z geek at large FastWoman's Avatar
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    Congrats!!

    Wow, I sure am glad we don't have smog testing here in VA, not that my exhaust would be that awful. It sure must be a PITA!
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    Registered User grantf's Avatar
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    Curious: I think I have my AFM dialed in just about right, but I think I am running a little lean. So what is the difference between enriching the mixture through AFM adjustment and installing a resistor in line with the WTS that some have done?

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    Registered User rcb280z's Avatar
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    Never did the resister inline so I'm not really sure of the difference other than being able to do it while you are in the drivers seat while driving. I'm getting between 22 and 25 mpg right now and my plugs look good. She runs very well.

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    Boat Anchor Repairman Captain Obvious's Avatar
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    I don't know how sensitive the idle mixture adjustment screw is. I also don't know how much throttle opening you needed to maintain that 15 and 25 mph on the dyno, but remember that since the bypass screw is in parallel with the throttle butterfly plate, it will have more impact the less the butterfly is open. In other words, if you close that screw down some, it will make you richer across the entire operating range, but the change towards richer will be greater at idle than at WOT.

    I'd be interested in hearing how much of an effect that screw has for say one turn or so.

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    Registered User rcb280z's Avatar
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    Ok here we are. The HC dropped slightly when we adjusted the bypass screw in the AFM richer "CW". 1 full turn took CO from 0.01 to 0.28 still way within spec. This was the 15 mph dyno run. Took it out for a spin and am very happy with how she is running. I can't remember what the 25 mph dyno numbers were but they only increased slightly as well. Going to run it around a couple more times and then check plugs. If they look good I'm going to stop with adjustments. She is running fantastic!

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    Boat Anchor Repairman Captain Obvious's Avatar
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    Quote Originally Posted by rcb280z View Post
    The HC dropped slightly when we adjusted the bypass screw in the AFM richer "CW". 1 full turn took CO from 0.01 to 0.28 still way within spec.
    Isn't it great when stuff happens the way it's supposed to?? I find it even more satisfying that you made it a little richer and the HC went down.

    Thanks for the numbers for one turn. I know each car could be different, but it's a benchmark!

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    Registered User rcb280z's Avatar
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    Default my pleasure.....

    Capt, it is great to see it work the way it is supposed to! I would imagine that if I continued adjusting I would hit a spot when the HC would start to increase due to being too rich....engine can't get enough air to properly burn the fuel and the catalytic converter can only take so much as well. Going to take it out for a good run today. Maybe put a couple hundred miles on her and then check the plugs. If they look good I'm done! Then I can install my new aluminum radiator I got at MSA during the April show. Going to pick up my new (original) hood and start that project as well. It looks good now but I like the original look better.
    Last edited by rcb280z; 05-21-2012 at 07:57 AM.

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    Registered User grantf's Avatar
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    Quote Originally Posted by Captain Obvious View Post
    I don't know how sensitive the idle mixture adjustment screw is. I also don't know how much throttle opening you needed to maintain that 15 and 25 mph on the dyno, but remember that since the bypass screw is in parallel with the throttle butterfly plate, it will have more impact the less the butterfly is open. In other words, if you close that screw down some, it will make you richer across the entire operating range, but the change towards richer will be greater at idle than at WOT.

    I'd be interested in hearing how much of an effect that screw has for say one turn or so.
    I really have not played around with the idle Mixture screw. Hmmm I may need to look into that. It is between 800 and 1800 rpms that my car runs a little rough it seems.
    rcb280z I am impressed that you get the mileage that you do. I have improved mine from about 9 mpg to close to 18.

    And I think your cae could use a different hood.
    Last edited by grantf; 05-21-2012 at 05:20 PM.

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    Since I recently installed a different AFM with a lean spot right off idle, I've tried adjusting the idle air screw to give a little more fuel when the AFM vane is almost closed. It had almost no effect on the flat spot, but did make the idle exhaust smell more gassy.

    On the other hand, I had also installed a potentiometer on the coolant temp sensor circuit to test what I thought might be excessive leaning as the cause of the "hot start" problem. The knob is in the cabin so I can adjust on the fly. Adding fuel there does clear up the lean spot.

    So, in my experience, the idle air screw definitely affects the idle mixture but not much else. Just some recent results from my experiments. The idle screw can be reached easily though, so it's pretty easy to verify if you have a very short flat blade screwdriver.

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    Registered User grantf's Avatar
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    That is one of my main problems right now, the "hot start" symptom. The only thing is it seems sort of odd to be tuning the car from the drivers seat. Alas it seems that it may be the thing to do. Still My EFI was pretty messed up when I got the car and that screw setting is one thing I have not verified as being set correctly. Is there any way to know at least what the initial setting should be? I get a small amount of front fire after a hot start.
    Not trying to hijack the thread.

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    Registered User ZCurves's Avatar
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    This great news! I am still going through mine. I have installed a new Distributor and set the timing, now I am checking and adjusting everything else. My Z runs pretty well, its just that I believe it is too rich and I really do not feel that it is as "nimble" as I remember it to be...maybe because I am 75lbs heavier now . I am working through all of the write ups from Atlantic Z Club. I will be looking over the TPS and the Air-Bypass. rcb280z, can you recall the number of turns (from bottom out) on the Air Bypass screw that put you in the sweet spot to pass your smog?? Thanks
    Andrew (ZCurves)
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    Registered User rcb280z's Avatar
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    Andrew, Actually I think it is about 3 full turns CW from being completely "out" CCW. That is the bypass screw is flush with the AFM body and then 3 full turns in CW. It worked for mine but may not work for you. It all depends on what kind of shape everything else is in...tps, afm, aar, injectors, fuel pump, fpr, etc, etc. I had a problem with corrosion in connectors & wiring and replaced everything affected. Then you really need an analyzer of some sort to give an idea if you are heading in the right direction. Mine was trial and error. I really spent a lot of time on the afm! I will take a couple of pics of the inside of mine this weekend that may help you. It will show you one important adjustment. Again it worked for me and may not for you but is worth a try. You can always put it back to your last setting. Have you tested your TTS, and WTS when the engine is hot and cold? A Lot of the time a rich condition (except for mine) is due to a faulty thermotime and or water temp sensor. So check everything else first. How much vacuum are you pulling. I'm at 19 with 10 BTDC timing and 800 rpm with over 276,000 miles. 186,000 after my basic overhaul. So I'm doing good except for the coolant weep at the head. Keep me posted on your progress and I will try to remember to post those pics. You can tell if your aar is working properly also by connecting a good vacuum gauge to your intake and when the ingine is cold start it up and watch the vacuum gauge. Mine started at 14 (aar vacuum leak) and as it slowly closed my vacuum slowly increased to 19. Kinda cool to watch. Anyway, good luck and post results.
    Last edited by rcb280z; 05-22-2012 at 10:45 PM.

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    Registered User ZCurves's Avatar
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    I would say you are doing exceptional to have those numbers with that many miles... My engine has maybe 300 since rebuild. I did R&R on the entire harness and every component, but I could still have bad TTS and WTS - Thanks that is good advice. I will also go over my vacuum too. It is going to be a busy Memorial Day Weekend..
    Andrew (ZCurves)
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    Registered User rcb280z's Avatar
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    Default Forgot something...

    My 77 280Z passed CA smog with better numbers than our 05 2.5 Nissan Altima! Not that the numbers are bad for the Altima just that for some reason the altima is allowed higher emissions numbers! Doesn't make any sense to me. Oh wait, it's CA! It makes sense now.

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    Registered User ZCurves's Avatar
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    Nice, I have an '09 Altima too - something else to look forward to (although not as strict as CA).
    Andrew (ZCurves)
    1978 Coupe - HLS30-440105
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