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

[Captain Obvious]

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!

[rcb280z]

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.

Edited May 21, 2012 by rcb280z

[grantf]

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.

Edited May 21, 2012 by grantf

[Zed Head]

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.

[grantf]

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.

[ZCurves]

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

[rcb280z]

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.

Edited May 23, 2012 by rcb280z

[ZCurves]

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..

[rcb280z]

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.

[ZCurves]

Nice, I have an '09 Altima too - something else to look forward to (although not as strict as CA).