adjusting air fuel mixture/ratio
Hi everyone. So my car was having a lean misfire. You could hear the exhaust popping when you held down the gas peddle at a consistent rpm. I went o my friend who is a mechanic and he said he adjusted the mixture by turning a screw on the mass air flow. The car was instantly better but it still popped a little bit out the exhaust at low rpms. I went to fiddle with the MAF but I screwed it all up now. The popping is gone but I can smell the exhaust a lot more and at higher rpms the car vibrates because I believe there is too much fuel and not enough spark. Some people told me to adjust it till the idle is at 800 but the idle screw has also been tampered with so its no longer an accurate measure to work off of. Plus there is supposed to be an idle bypass in the mass air flow anyways. How do i get the air fuel mixture and idle back to where they should be stock? I need to know as soon as possible because my school (UTI) is giving me the priveledge of dynoing my car on thursday. Can anyone please help?
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"default setting for idle air screw is 6.5 turns out from full rich. I cranked it in 3 turns and got it to idle a hair better. After test drive, car hot, 17.5" of vacuum."
http://www.zcar.com/70-83_tech_discussion_forum/is_it_time_pull_head_894425.165.html
http://www.zcar.com/70-83_tech_disc...gulator_bad_893825.msg2683010.html#msg2683010
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http://www.zcar.com/70-83_tech_discussion_forum/is_it_time_pull_head_894425.165.html
http://www.zcar.com/70-83_tech_disc...gulator_bad_893825.msg2683010.html#msg2683010
learn more about your car for a start. you have an air flow meter not a maf. that unit appeared on the z31. get the fsm. download the fuel injection bible.
I actually own the original repair manual but it doesnt say anything about adjusting the air fuel mixture in there. So if what we were adjusting only affects the air/fuel mix at idle, why did it get rid of my popping sound in my exhaust at 2000+rpm? I dont see how that makes any sense. And for anyone who thinks I might have a faulty AFM, I have 3 and they all work exactly the same. Also why is the car now vibrating at 70+ mph? I figured it was due to it running so rich that there was too much fuel for the spark. For a matter of fact the whole car feels different accelerating at anything above 3500 rpm. Also my throttle response is much poorer. How does this make any sense if the only thing we touched was just supposed to adjust my mixture at idle? Im lost. Also just double checking, to turn the mixture more rich you turn the screw counter clockwise and to make it more lean you turn it clockwise? I think this is right but I just want some confirmation. Thanks guys for all the help.
"I actually own the original repair manual but it doesnt say anything about adjusting the air fuel mixture in there. "
Uh, then what might you deduce from that fact? Seriously, if it's not in the FSM might there be a REASON it's not in there?C'mon now, THINK, I know you can do it. Cogitate on it a bit. Perhaps this will help:
"And for anyone who thinks I might have a faulty AFM, I have 3 and they all work exactly the same. "
Now let's put 2 and 2 together....no guidance in the FSM, three components doing EXACTLY the same thing...C'mon, c'mon...
Seriously is this that hard to grasp?
"I think this is right but I just want some confirmation."
No confirmation, other than you're screwing things up. Adjustment of the AFM will screw up your car 999 times out of 1000. It's just people screw with it and the terribly coarse adjustments they make so severely alter the way the car runs they perceive it as 'doing something' and of course 'something is better than nothing'... I posit you go back and learn about the Bosch EFI system, you quickly learn simple mechanical maintenance is all that is necessary to keep it working right. You start fu.king with the electricals, and you're done.
Uh, then what might you deduce from that fact? Seriously, if it's not in the FSM might there be a REASON it's not in there?C'mon now, THINK, I know you can do it. Cogitate on it a bit. Perhaps this will help:
"And for anyone who thinks I might have a faulty AFM, I have 3 and they all work exactly the same. "
Now let's put 2 and 2 together....no guidance in the FSM, three components doing EXACTLY the same thing...C'mon, c'mon...
Seriously is this that hard to grasp?
"I think this is right but I just want some confirmation."
No confirmation, other than you're screwing things up. Adjustment of the AFM will screw up your car 999 times out of 1000. It's just people screw with it and the terribly coarse adjustments they make so severely alter the way the car runs they perceive it as 'doing something' and of course 'something is better than nothing'... I posit you go back and learn about the Bosch EFI system, you quickly learn simple mechanical maintenance is all that is necessary to keep it working right. You start fu.king with the electricals, and you're done.
I think your friend the mechanic isn't so good a mechanic for z cars as he doesn't seem to understand the system.
These are all valid points but they are also useless to this thread. In either one of those comments did I find any information on how to repair an issue with my Z. Id like to keep this thread on track.
Get some bright lights, or the sun, and a magnifying glass and see if you can match up the original factory glue marks.
It does sound funny, but I think it would actually work. Unless the sprocket has been turned around more than 360 degrees, which is not likely.
Lionel280z, yes the idle air screw richens up the idle mixture when the screw is turned in. All it's doing is blocking an air passge that bypasses the vane. And if you live in a metro area in Portland it will cause you to fail the emissions test. Alternatively, if you fail the test, back the screw out until you pass.
Edit - the stuff below won't really help with adjusting the spring tension but might help in seeing if your potentiometer is right -
I just realized that I had posted some numbers over on classiczcar that might help you out. Some one is having tuning problems there so I measured the voltage range from closed vane to open vane on a spare 1978 AFM that I have. The AFM came from a running car, although I never did drive it, just ran it in my garage. But, of course, it "ran great when parked!". It ran great in my garage also.
If you can get your AFM to match these numbers, you should be as close to stock as you'll ever get. Note that the battery I used was putting out 12.89 volts, so if yours doesn't you might have to estimate up or down a little. Be very careful if you try this because the two pins that you apply 12 volts to are right next to each other and you could melt your test leads. You'll need some wire with alligator clips or make your own with female ends to fit the AFM. Or you could work from the ECU connector if you don't want to take the AFM completely out. This is the same test from the FSM, but I actually measured voltages, the FSM just recommends watching the smoothness of the voltage drop as the vane opens.
1978 AFM
Pin 8 to 6 - 182 ohms resistance
Pin 8 to 9 - 102 ohms
Apply 12.89 volts across pins 9 and 6
Measured 6.6 volts across 7 and 8 with vane closed
Measured 0.17 volts across 7 and 8 with vane open
Smooth rise and drop
Lionel280z, yes the idle air screw richens up the idle mixture when the screw is turned in. All it's doing is blocking an air passge that bypasses the vane. And if you live in a metro area in Portland it will cause you to fail the emissions test. Alternatively, if you fail the test, back the screw out until you pass.
Edit - the stuff below won't really help with adjusting the spring tension but might help in seeing if your potentiometer is right -
I just realized that I had posted some numbers over on classiczcar that might help you out. Some one is having tuning problems there so I measured the voltage range from closed vane to open vane on a spare 1978 AFM that I have. The AFM came from a running car, although I never did drive it, just ran it in my garage. But, of course, it "ran great when parked!". It ran great in my garage also.
If you can get your AFM to match these numbers, you should be as close to stock as you'll ever get. Note that the battery I used was putting out 12.89 volts, so if yours doesn't you might have to estimate up or down a little. Be very careful if you try this because the two pins that you apply 12 volts to are right next to each other and you could melt your test leads. You'll need some wire with alligator clips or make your own with female ends to fit the AFM. Or you could work from the ECU connector if you don't want to take the AFM completely out. This is the same test from the FSM, but I actually measured voltages, the FSM just recommends watching the smoothness of the voltage drop as the vane opens.
1978 AFM
Pin 8 to 6 - 182 ohms resistance
Pin 8 to 9 - 102 ohms
Apply 12.89 volts across pins 9 and 6
Measured 6.6 volts across 7 and 8 with vane closed
Measured 0.17 volts across 7 and 8 with vane open
Smooth rise and drop
http://atlanticz.ca/zclub/techtips/afm/calibration/index.html
Okay thank you blue for the link. PDX280 I'll look into that this weekend when i have a space to work in (apartment not very accommodating). Im going to mess with the idle screw a little more tomorrow. I think I am very close. Another question I have is after looking on the atlantic z site they show a way to richen the air fuel ratio by taking apart the airflow meter and adjusting the spring. Does anyone suggest this with an entirely standard motor? Should I upgrade to the 280zx distributor first so I'd have a better spark for all of that fuel? I do daily drive my car but I am looking for more performance than gas mileage. Thanks everyone
Actually, what I posted about measuring output voltage is only relevant to seeing if your potentiometer works right. It won't help with adjusting the spring, since that just determines how much air it takes to move the potentiometer.
My mistake.
My mistake.
In your first post you said "I went to fiddle with the MAF but I screwed it all up now. ". But now you're talking about "taking apart the airflow meter and adjusting the spring." How did you screw it up the first time, if you weren't adjusting the spring?
I wouldn't upgrade anything until the stuff I already had was working.
I wouldn't upgrade anything until the stuff I already had was working.
This is what was making me confused. I never messed with the spring but the car still acted like I was adjusting the air fuel ratio by turning the screw for the idle adjustment. All of a sudden today the car was running perfectly. No sounds out of the exhaust and had plenty of power. It also wasnt shaking on the freeway anymore. It seems like I have a phantom issue with my car.
Check all the wiring connections in your efi system and clean them.
I checked them all but im really going to clean them this weekend for some piece of mind.
That, sir, is because you don't want to HEAR what people are telling you. Those too stupid to hear the train are fodder to get run over by it. Good luck with your 'diagnosis' --- keep replacing what YOU think it is, eventually you will stumble across it.lionel280z said:These are all valid points but they are also useless to this thread. In either one of those comments did I find any information on how to repair an issue with my Z. Id like to keep this thread on track.
Or not.
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