I have a 78 280z and wonder what the two screws (they have rubber plugs covering them) that are located on each side of the lower out take port (the side that is closest to the throttle chamber) are designed to do. When I cleaned the air flow meter, I noticed that the screws seem to adjust the size of an air bypass port channel. I have played with the adjustment and have likely adjusted the setting out of the factory setting. Can anyone tell me what the function of the two screws is and how I should adjust them to get them close to the factory setting? Is there a test to see if the air flow meter is functioning properly? Lastly, does my car have an air temperature sensor on the air flow meter? Thanks for your help in advance.

Those are the air bypass screws. I wouldn't play around with them too much wihout some sort of meter to read the air/fuel mixture, CO, etc. because that's what it will affect. I use a Gunson Gastester for that ususally every other year just before I have my car smog checked. The air temp sensor is located just in front of the flap in the AFM. It's the white plastic thing sticking out into the opening on the air cleaner side of the AFM.

THanks for the reply. I presume that the temp sensor is not visible from the outside. I cannot see any connection apparent on the outside except the multi-contact connector that is black.

Can you give me a rough idea of how many turns from a seated position (all the way in) the two screws are backed out in your AFM?

Seated? As I recall, those screws will go a long way down. I've never had them all the way in on either car. I make my adjustments based on the readings on the meter I use.

Higuys,

What kind of places have the equipment or knowledge to adjust these things properly? What kindf stuff should you be looking for- O2 or HC meter? My AFM hasn't been checked in a few years now. It's about time for a tuneup and get the AFM stuff checked too.

thxZ

I try to get the CO% in range. With that in the correct range, about .6% @ 15mph, 1st gear and .2% @ 25mph, 2nd gear, everything else, HC, NO, air/fuel ratio seem to fall in place. At those readings, may cars get the best balance of performance, fuel economy and they pass the smog check well below the max limits.

My 280Z is already way below all the limits for everything, but if I can, I will get the AFM checked again, including the idle readings.

thxZ

It's a delicate balance. You don't want to be too far below or it takes other parts out of whack. At idle the air/fuel ratio should be as near to 14.7:1 as possible. That's what I use as a benchmark before I do the CO% settings. I use a different tool for that. It's easier for me to do it than it is to explain it. There are several steps it. But my results are such that I've never failed a smog check with either of my EFI cars. But I cringe when I hear about someone adjusting the AFM without the proper tools or knowing what the range of the settings should be. You can't really just tighten or back out the adjustment screws on EFI without having some kind of way of knowing the readings those adjustments create. It isn't 'x' number of turns in or out, like carbureators. It differs from vehicle to vehicle

OK, I finally found it; "bypass screw" in Section ET (Engine Tuneup) page ET-8. The spec for CO is 0.5% for CA cars,and 1% for Fed. cars. the timing and RPM specs vary for manual or automatic transmissions.

You might be right, that having emmissiond TOO low, might mean that the engine isn't getting the right fuel mixture, and maybe even not performing as it could, so that is why I will get it checked when I can.

thxZ

Well, I used to use those settings but .5% at idle decreases too much by 1/4 to mid throttle and in doing so skews the readings that are used for the California test. That's why I use the A/F ratio at idle and run the other tests at the speed/rpm that is used for the test. Being in Ohio you probably don't have to deal with all of that. If Cali had their way, we wouldn't be driving older cars. The limits are more stringent for my 810 and Z than they are for newer cars like my wife's HHR. I've experimented enough to come up with what works for the system I have to work with and then I readjust for the way I really want the car to run in between smog checks.