I have a 1978 280z 5 speed. It has the AFM on it, that has an air bypass screw on both sides of the AFM. Can someone tell me more about them, when to adjust them, when to leave them alone etc? I searched the forums and didnt really find what I was looking for. For one thing....turn CW will richen the mixture and turning CCW lean it out, is that right?

What is the way to adjust the CO readings on the car (assume a normal running engine)? Do you just need to adjust the AFM screw(s), or do you also have to adjust the air bypass screw(s) too?

Lastly, does the idle adjustment spring and the AFM air bypass screws work in conjunction with each other? I dont understand yet how adjusting one, will effect the other, and vice-versa.

It seems if I would turn the AFM bypass screws to richen or lean out the engine, that its going to effect the idling speed of the engine because more or less air will be going into the running engine. So it seems like if youre idle is set OK to say 800 or 900, but then you need to adjust the AFM screw in order to change the CO readings, in the process of doing that, the idle is going to change. SO it seems like a cat and mouse game.

I do have an innovate AFR meter at least, so I can get some readings. But I dont have a CO meter to monitor that.

Without some data about where you are at, it doesn't make sense to change anything. What are your numbers? The bypass screws are more about idle than anything else. I wouldn't stress over them.

I wouldn't touch the bypass screws w/o something to monitor the changes in both AFR and CO (which I do have). That being said there's really not much to gain from adjusting them (as Rob said) since the changes will basically only affect the idle.

I just want add that I said 'basically only affects the idle'. To be a little more accurate, based on tests I've done, I should have said that the more the flap is open, the less effect the bypass screws have. This is important for California emissions testing since that is done at part throttle in an area where the bypass screw adjustment would still have some effect.

Well yes, I have the innovate LM-1 meter hooked up now with the exhaust clamp. And have run two tests so far. I had a local mechanic doing some other testing if you read this thread...you can find out more about what I have been doing lately. http://www.classiczcars.com/forums/showthread.php?41966-noob-valve-adjusting-on-1978-280z

As far as AFR numbers, well that are not looking good at all. WOT is like 10.1 or 10.2, crusing is averaging maybe 12.5. Idling seems to be very lean now at least around 18.x, but I am pretty sure I saw the AFR LED screen showing 25 to 29 AFR when sitting at stop signs. This gets back to my low vacuum condition I am getting close to adjusting valves. That other thread above is where I am asking for help on that issue.

I made a video of the innovate tests results during the two test drives. So some friends of mine who dont have the software could at least see the AFR data as I went on 44 minute long test drives because I ran the LogWorks software, and captured screen videos and added great color commentary and saved the screen videos as wmv files.

It seems from what I remember reading, that the AFR bypass screws are used to make CO adjustments. But one thing I was wondering, do both the screws only effect at Idling? Or is one of them made to adjust for when car is running down the road and NOT idling?

And why are there even two of them in the first place? I would kind of like to understand that a little better. Thanks

PS Is there a CO meter that is affordable? It seems when I was looking a while back, they were all pretty expensive for my tastes.

Edited April 15, 201113 yr by argniest

It's a rather primitive system that is often over thought when trying to troubleshoot it. The two screws are somewhat redundant, IMO. They're on opposite sides of the same bypass port in the AFM so they both do the same thing, which is allow the engine to run with the flap closed. And once the flap is open enough, they don't really do anything. I use a Gunson Gastester to test CO. Bought it years ago when they were somewhat reasonable and it still works fine.

Its kinda of funny and interesting to me, why we need two screws on the AFM that apparently do the same thing. Is it just so that they can let air bypass equally on both sides of AFM body?

Does adjusting them serve the purpose of adjusting the CO of the engine? I still have a lot to learn about my engine and how it relates to CO settings.

How is the CO adjusted when car is running down the road? I suppose the answer to that, is to have your engine is good working order and then it *should be* OK. It sounds like these two AFM screws are only when car is sitting an idling.

Is this the device you have: http://www.amazon.com/Gastester-portable-powered-exhaust-analyzer/dp/B000RT8ER0

I also found this one: http://www.etoolcart.com/gunson-gastester-portable-exhaust-gas-analyzer.aspx for less than 300$

hmmmmm

I also thought someone was telling me that measuring CO without being able to also measure HC's at the same time is kind of pointless. But I dont remember anywhere in our manuals that says anything about measuring HC. They just have the specs on measuring CO from what I remember anyway.

Edited April 15, 201113 yr by argniest

I am wondering why you are focusing on the AFM? Your rich part throttle numbers lead me to believe your problem is elsewhere. The AFM is approximating how much air is coming in. TPS, WTS, CHT and injectors are effecting fuel.

Ok, after reading your other thread I have a bit more to work with. You state you have the FSM. Good. In there you will find a proceedure for troubleshooting and tuning. You must follow the procedure in the order they prescribe. One thing effects the next. Don't follow the path of least resistance. Some people will check the fuel pressure because they don't know how or don't have a feeler gauge for the valve adjustment. Don't get caught in that trap. Very little about this LJet system has adjustment. Mostly it requires service on vacuum and injectors. If you want to continue your fuel system refresh (I would from what you described) I would pull the injectors and send them out for a rebuild and calibration. Sticky injectors will increase your HC and CO especially at idle. This gives you an opportunity to replace those 33 year old high pressure fuel lines. Be sure to use hose rated for EFI! Marren and RC engineering come to mind for injector rebuilding.

Next, I would find and fix any and all vacuum leaks. Any and all adjustments are pointless with a vacuum leak. EFI hates vacuum leaks.

Adjust your valves. Did I mention that you should adjust your valves?

If all the sensors are sensing, and the vacuum leaks have been conquered and the injectors are in good service, EFI requires very little adjustment. My bottom line point is that any adjustment without these things taken care of is pointless and costs you money. There was a guy who used to have an EFI video he sold, I think his name was Scott Bruening? Anyway, he owned Z Therapy before the current owners. If I can paraphrase him - most fuel injection problems are not fuel injection problems at all.

Edited April 15, 201113 yr by conedodger

BTW conedodger, I did replace fuel injectors :-) just a few weeks ago with brand new ones (that was NOT an easy process for me, but I was very thoughtful and careful and the local mechanics who did the smoke tests, ingition testing with oscilliscope computer, and timing changes, (as described in my other post) thought the FI's were fine. Also, you can hear them all clicking the same degree of loudness when you listen to with a stethescope). Also, yes, I replaced every single fuel related hose from the tank to the injectors, with EFI rated hoses where needed, and I cleaned metal fuel rail while it was off the car, shot carb cleaner thru the metal fuel lines under the car a bunch of time, which did remove a little debris. Did it until they were clean looking from bucket contents that it was emptying into. And I installed that G3 fuel filter back by gas tank, so I can see into it, and tell if anything is getting into fuel system. but with the gas tank being cleaned and sealed, I should hardly ever see anything in there, unless the gas station has bad gas storage tanks.

And there are no fuel leaks anywhere. I have checked many times now. Those hoses/clamps are good. I also had the local mechanics dbl-checking my clamping, and they said I did a good job on all of them. And they did the smoke test for 5 minutes and we didnt see anything anywhere. No smoke coming out. It made me feel somewhat better that I dont have any vacuum leaks. Their opinion was I DONT HAVE ANY INTAKE VACUUM LEAKS I want to agree with them, but am not 100% sure of course.

I have found and fixed some cracked/split hoses this winter. And I thought I have clamped down any loose hoses like on Aux Air Reg for instance.

Does that help with what you said above...?

HEHE :-) ADJUST VALVES. I am hoping with help from a friend and your guys advice to be doing a valve inspection starting 2night. And adjustment if needed. Ive got to get get a good quality ft-lb wrench tonight first of all, but I have the feeler guage set and wrenchs I need otherwise.

I am very hopeful that valves will need some adjustment and after doing it, she will come back to life much more than now. I mean as its driving now, I could live with it. Because it is running better than ever before. However I am getting really bad gas milage, so I know I cant stop yet. Valve adjustment could be THE TICKET!!!! It may not solve all remaining problems, but I feel like it could give me the most bang for my dollar and a half.

I will also be checking the TVS as soon as I can. I know that can cause problems. There are soooooooooooooooooooooo many pages and pages and pages and pages of troubleshooting procedures between FSM, EFI bible etc. Its very daunting. I mean I have done some of the recommended things, and repalced many old parts with good quality name brand OEM where possible, parts. And I will keep at it, but I just hope I can get the valves adjusted and see a good performance gain out of it. I will be relentless to go through every diagnostic procedure that seems to apply to my sitation. But it will take me a long time to figure them all out. I have learned a lot about the car since getting hands dirty for past 6 months, slowly but surely, but have a much longer way to go!!!!!!!!!!!!!!!!!!!

Edited April 15, 201113 yr by argniest

Is this the device you have: http://www.amazon.com/Gastester-portable-powered-exhaust-analyzer/dp/B000RT8ER0

I also found this one: http://www.etoolcart.com/gunson-gastester-portable-exhaust-gas-analyzer.aspx for less than 300$

That's the one although they both look like later models.

That's the one although they both look like later models.

So, when you are using this meter, how (or what) are you adjusting on the car, to adjust your CO readings? I am reading over what someone just wrote back to me above, and it seems like there are not many things to actually adjust in this old EFI system in the Z car. Basically you have to get rid of any/all vacuum problems, and make sure your valves are proper, timing proper, and good fuel delivery system/EFI system from gas tank to injector. I mean, those are things you cannot tweak. They are just there, and neeed to be working properly.

FAIW, I've turned those stupid idle mix screws back and forth, with apparently no effect. I'd be very interested to see what sort of effect that adjustment has on the exhaust readings! I'll stay tuned.