Takeing the AFM apart.
02-22-2003, 09:52 PM
#1
Nordschleife Master
Thread Starter
Takeing the AFM apart.
How do I get the AFM apart?
I noticed there is a sealed seam on the bottem side, but I can't get the bottem off.
I don't want to break the thing, but I can't figure out how to get it apart!
Suggestions?
I noticed there is a sealed seam on the bottem side, but I can't get the bottem off.
I don't want to break the thing, but I can't figure out how to get it apart!
Suggestions?
02-23-2003, 01:47 PM
#2
Nordschleife Master
Thread Starter
Somebody please help me here.
I'm still trying to trouble shoot my rich idle problem.
No matter which way I turn the mixture adjustment screw, stop to stop, I always get the same O2 sensor reading. My gut is telling me something is blocking off the by pass channal, at least partly.
How do I make sure the by pass channal is clear?
Thank you
I'm still trying to trouble shoot my rich idle problem.
No matter which way I turn the mixture adjustment screw, stop to stop, I always get the same O2 sensor reading. My gut is telling me something is blocking off the by pass channal, at least partly.
How do I make sure the by pass channal is clear?
Thank you
02-23-2003, 03:01 PM
#3
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VU,
It sounds like your car is running at the default mix (afm not working). But you should probably troubleshoot all the other possible problems before you rip the afm apart.
Try driving the car with the adjustment screw at each stop to insure that you are not just looking at a bad o2 sensor?
You certainly *do* have a way of finding yourself with some interesting problems...
It sounds like your car is running at the default mix (afm not working). But you should probably troubleshoot all the other possible problems before you rip the afm apart.
Try driving the car with the adjustment screw at each stop to insure that you are not just looking at a bad o2 sensor?
You certainly *do* have a way of finding yourself with some interesting problems...
02-23-2003, 03:26 PM
#4
Nordschleife Master
Thread Starter
I've tryed adjusting the car to each stop. It acts the same all the time. It's as if the screw doesn't do anything. The only way I could see this happening in the various diagrams, is if something else was cloging up the by-pass. To test this theory, I found I can't push a thin rubber vacume hose down the bypass, except for like an inch. Eighter there is a ridge thatI don't know about in there, about an inch down, OR there's something partaly blocking the by pass.
When I pull the O2 sensor, there is a nearly instant drop in the rpms. Between 50-100. The idles goes from reletivly smooth, to a 75 or so rpm up and down flux. The voltage from the O2 sensor stabilizes around .84-.86 V
The engine will not run with the AFM unpluged. The AFM matches the resistance values given in the service mannual.
I know I have a way of finding intersting problems. However, intersting problems beat the heck out of boreing ones!
When I pull the O2 sensor, there is a nearly instant drop in the rpms. Between 50-100. The idles goes from reletivly smooth, to a 75 or so rpm up and down flux. The voltage from the O2 sensor stabilizes around .84-.86 V
The engine will not run with the AFM unpluged. The AFM matches the resistance values given in the service mannual.
I know I have a way of finding intersting problems. However, intersting problems beat the heck out of boreing ones!
02-23-2003, 11:32 PM
#5
Nordschleife Master
Thread Starter
This thing has finaly reached my level of tollorance.
After I get off the gas, after a fast acceleration (like between stop lights, at the next red light...) the idle falls, and the recovers, just like when I unplug and then plug the O2 sensor.
Tonight, after a quick stop light run, I stoped for the red light, and the idled droped so far the engine died, before the computer cought the message and could fix it. She started right up again.
That is just past the very edge of my tollorance.
Is my mixture so rich that the engine dies? It's only reading .9 V at the most when I check it. Most often .85 or so.
I've adjusted the idle to the high side of the range, and the ignition timeing is spot on 10 degrees BTC, at idle.
Temp II checks out, Thermo-time unpluged, AFM matched the resistance values, the door swings smoothly, new vacume lines to all the limiters. All have solid vacume. The various actuaters don't leak.
What am I missing?
After I get off the gas, after a fast acceleration (like between stop lights, at the next red light...) the idle falls, and the recovers, just like when I unplug and then plug the O2 sensor.
Tonight, after a quick stop light run, I stoped for the red light, and the idled droped so far the engine died, before the computer cought the message and could fix it. She started right up again.
That is just past the very edge of my tollorance.
Is my mixture so rich that the engine dies? It's only reading .9 V at the most when I check it. Most often .85 or so.
I've adjusted the idle to the high side of the range, and the ignition timeing is spot on 10 degrees BTC, at idle.
Temp II checks out, Thermo-time unpluged, AFM matched the resistance values, the door swings smoothly, new vacume lines to all the limiters. All have solid vacume. The various actuaters don't leak.
What am I missing?
02-24-2003, 01:21 AM
#6
Photoshop Bully
Rennlist Member
Rennlist Member
Grab a seat, this is a long one. As far as AFM surgery goes. DON'T DO IT. I used to be heavily into 280Z's and ZX's in my younger days. They ran a Bosch injection w/ an AFM. Every time I opened an AFM with the thought of fixing a problem or adjusting my way around another problem, it ALWAYS came back to bite me in the a$$. Mostly in the form of compromised performance or the car wouldn't run right all the time. Running great cold, meant running crappy hot, or vice versa. This is why the cover is bonded onto the AFM, they don't want you in there. Your probably one of those people who jaywalks and rips off mattress tags too! Try to bump up your tolerance a little, you'll be glad you did. Every time I messed w/ a Nissan AFM, I would go to the junkyard and buy another for $20 along w/ other FI doo dads. You don't have that option w/o spending more $, and the yards aren't exactly littered w/ 928s. Now, to totally contradict myself, if I remember correctly, on the Z AFM's there was a switch inside that would turn on the the fuel pump when the AFM door was swung off its closed (car not running) position, hence the glorious vroom we all love to hear. Now, this was ions ago so I may be a little fuzzy on all of this. Seeing as 928's like to idle low, maybe you have a vacuum leak somewhere and the door isn't in sync w/ the air demands of the motor or the switch may be flaky (if there is one). Maybe you could try putting an indicator light on your fuel pump relay feed and go for a blast w/ a friend who likes to stare at test lites while being driven around recklessly to see if the light stays on when the car stumbles. Next, the inside of the AFM has a variable resistor that sends a value to the computer for mixture data. The thing looks like the inside of a hard drive where the p/u arm contacts the disk, or like a record player arm contacts a record. There is a toothed plastic gear that has a locking screw on it. When you loosen the screw you can adjust the spring tension of the AFM door which alters the signal to the computer to "fool" it into being richer or leaner, depending on which way you adjust the spring pretension. The problem is that when you adjust the AFM to get a better idle, you've essentially adjusted the mixture of the whole AFM range. Which would effect engine performance throughout its entire RPM range. Which masks one problem by creating another somewhere else. Of course all of this is based on my Z car experience, but it was still a Bosch setup. Even when looking at a picture of a 928 AFM in one of my catalogs, it looks identical to the Z unit.
(Paragraphs, don't see them in forums too often) Once again, those vacuum leaks can be a b!tch. So take a good long look and listen. I own a 69 vette, so I know a thing or 2 about vac leaks, seeing as the whole d@mn car is vac operated. One last thing I see is that your running w/o felines. If you've run the car w/ any strange additives or leaded race fuel, the 02 is toast. Even spraying your engine w/ any lubricants or shiny dress up engine sprays that contain silicone can toast an O2 sensor instantly if it gets inhaled while the car is running. Thats it, I'm done. I have to go to bed now so I can pay for the second mortgage I'm taking out to buy 2 motor mounts for my S4. Goodnight and Good Luck.
(Paragraphs, don't see them in forums too often) Once again, those vacuum leaks can be a b!tch. So take a good long look and listen. I own a 69 vette, so I know a thing or 2 about vac leaks, seeing as the whole d@mn car is vac operated. One last thing I see is that your running w/o felines. If you've run the car w/ any strange additives or leaded race fuel, the 02 is toast. Even spraying your engine w/ any lubricants or shiny dress up engine sprays that contain silicone can toast an O2 sensor instantly if it gets inhaled while the car is running. Thats it, I'm done. I have to go to bed now so I can pay for the second mortgage I'm taking out to buy 2 motor mounts for my S4. Goodnight and Good Luck.
02-24-2003, 01:29 AM
#7
Rennlist Member
Have you checked the AFM resistance readings AT THE BRAIN? This will verify that the brain is seeing the readings, not just that they are ok. All sensor inputs to the brain should be checked at the plug/connector so you know the sensor is good, and the wiring from it to the connector is good.
Also, do the readings change when you move the adjuster from one end to the other? If not, there is something wrong with the AFM, isnt there?
jp 83, running on instinct, not brains.
Also, do the readings change when you move the adjuster from one end to the other? If not, there is something wrong with the AFM, isnt there?
jp 83, running on instinct, not brains.
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02-24-2003, 02:57 AM
#8
Nordschleife Master
Thread Starter
Why would adjusting the idle by pass have no effect on the idle mixture? I mean NO effect. O2 sensor give me the same reading no matter what I do with the by-pass screw. I've tryed it at both stops.
This is not the first time the engine died after running the stop light special. This is the time that made me mad.
I've pulled the brake booster line, induceing a lean mixture, and the sensor reflects this, falling to under 1 volt in a few seconds. My nose still works OK, and it's saying OK mixture when I've got the sensor pluged in, and way rich when it's unpluged. Yea, I'm careful about smelling exaust fumes. Only a second or so, and I know, rich or right. I can't smell a lean mix, but a rich is pretty easy. My nose and the O2 sensor agree.
I haven't realy tryed a richer mixture. I have hit the WOT enrichment switch, it causes the engine's idle to drop, just like when I pull the O2 sensor. If I give the ECU a second or so to read the O2 sensor after pulling it's plug, the mixture leans up, and the idle speeds up, so I know the O2 sensor is doing something.
As long as I've had the car, I've never used a silicone anything. I mean anything. I haven't even gotten around to useing it on the interor.
I've gone through the HVAC system. The vacume tank is disconnected as it has a huge leak, somebody else must have gone through the HVAC system, as all the actuaters hold vacume, and whole systems holds vacume from the line on the brake booster back. Checked with mity-vac.
The vacume limiting system for the distributer, control valves I and II, vacume limiter, fuel pressure damaner, and regulaters, is new. I re did it this weekend. Now the right stuff gets the right vacume. I checked it with the mity-vac.
I have a new AFM to pendilum seal, as I thought the last one was leaking. The seal I removed was in good shape, but the new on fit tighter.
I've been through the whole intake system, all 8 runners, listening for bad injector noises and possible vacume leaks. There were none that I could find. I've yet to do the cover-the-MAF-with-a-cut-inner-tube,-and-pressureize check just yet, but I will, soon. My ears are a bit tuned to listen to leaks by going through semi-truck brake systems. Plus I'm still young, and my ears are still sensitive. I also used the garden hose stetescope on it to no avail.
There is a "woosh" noise comeing from the by-pass line for the venture for the brake booster. I only hear it on the by pass line, not the area around it. The noise does not varry when I shake the line, and stops when I disengage the top of the line. I'm guessing it's just the sound of the air going though the line, but I'm not sure.
I'm 99% sure that it's not the fuel system causeing my rev-limiting miss. When I hit the miss, the tach nose dives, practicaly to 0. Once I let of the throtal, the tach picks back up to right under 4k rpm instantly. Something is killing the feed to the tach. That says transisterized unit, or pick up coil to me. My pick up coil seems to ohm out OK, I've yet to check the transisterized unit. It is a pain to try and get in and out. The pick up coil was acting like it was the problem, but that was probably a coincident, and now it's acting like it's not the problem. I'm buying a good external tach, and seeing if I can get conformation from the ignition coil while I drive it, to be sure I don't just have a flacky tack.
Heck, if the AFM is already busted, I'm not too worryed about breaking it. I'll ponny up the 100 bucks for a used on from the big three and call it good, but I hate to replace something I might be able to fix. I have dreams that a mud dobber got into the AFM, buit a nest, and pluged up the by pass. This, I could fix.
The thing that bugs me, is I can't figure out why the by-pass, a simple tube around the barn door, with a screw at the end of it, has no effect on anything. If it was a bad vacume leak, I'd have a lean engine. If it was a bad set of fuel presure regulaters, I'd be able to move the mixture more rich, or leaner. If it was a bad temp sender, I should be able to move the mixture up or down with the by-pass, and the ECU should innore the O2 sensor. If it was a bad AFM, I should still be able to adjust the idle mixture up or down with the by-pass. If it was a bad throtal load swith, they wounld't work, and it would innore the O2 sensor. If it was a leaky cold start valve I should still be able to make the mixture leaner, or richer.
The only conclusion I can some to is something is counter adjusting for me moveing the by-pass screw, or something is preventing the by-pass from working.
You see why this is frustrating? I can't get the mixture to move, EXCEPT by induceing alought of false air.
So, since the bottem of the AFM is just bonded to the rest of the caseing, I remove as much goop as I can, and just press it up and out?
Thank you for bearing with me. I'm trying to give you as much information as I can, so you can maybe narrow it down, or see what I'm missing. I'm getting good are removeing 928 intake peices.
Thanks for the suggestion jpitman, I'll check them at the brain next. Even that wouldn't explain why the by-pass has no effect.
This is not the first time the engine died after running the stop light special. This is the time that made me mad.
I've pulled the brake booster line, induceing a lean mixture, and the sensor reflects this, falling to under 1 volt in a few seconds. My nose still works OK, and it's saying OK mixture when I've got the sensor pluged in, and way rich when it's unpluged. Yea, I'm careful about smelling exaust fumes. Only a second or so, and I know, rich or right. I can't smell a lean mix, but a rich is pretty easy. My nose and the O2 sensor agree.
I haven't realy tryed a richer mixture. I have hit the WOT enrichment switch, it causes the engine's idle to drop, just like when I pull the O2 sensor. If I give the ECU a second or so to read the O2 sensor after pulling it's plug, the mixture leans up, and the idle speeds up, so I know the O2 sensor is doing something.
As long as I've had the car, I've never used a silicone anything. I mean anything. I haven't even gotten around to useing it on the interor.
I've gone through the HVAC system. The vacume tank is disconnected as it has a huge leak, somebody else must have gone through the HVAC system, as all the actuaters hold vacume, and whole systems holds vacume from the line on the brake booster back. Checked with mity-vac.
The vacume limiting system for the distributer, control valves I and II, vacume limiter, fuel pressure damaner, and regulaters, is new. I re did it this weekend. Now the right stuff gets the right vacume. I checked it with the mity-vac.
I have a new AFM to pendilum seal, as I thought the last one was leaking. The seal I removed was in good shape, but the new on fit tighter.
I've been through the whole intake system, all 8 runners, listening for bad injector noises and possible vacume leaks. There were none that I could find. I've yet to do the cover-the-MAF-with-a-cut-inner-tube,-and-pressureize check just yet, but I will, soon. My ears are a bit tuned to listen to leaks by going through semi-truck brake systems. Plus I'm still young, and my ears are still sensitive. I also used the garden hose stetescope on it to no avail.
There is a "woosh" noise comeing from the by-pass line for the venture for the brake booster. I only hear it on the by pass line, not the area around it. The noise does not varry when I shake the line, and stops when I disengage the top of the line. I'm guessing it's just the sound of the air going though the line, but I'm not sure.
I'm 99% sure that it's not the fuel system causeing my rev-limiting miss. When I hit the miss, the tach nose dives, practicaly to 0. Once I let of the throtal, the tach picks back up to right under 4k rpm instantly. Something is killing the feed to the tach. That says transisterized unit, or pick up coil to me. My pick up coil seems to ohm out OK, I've yet to check the transisterized unit. It is a pain to try and get in and out. The pick up coil was acting like it was the problem, but that was probably a coincident, and now it's acting like it's not the problem. I'm buying a good external tach, and seeing if I can get conformation from the ignition coil while I drive it, to be sure I don't just have a flacky tack.
Heck, if the AFM is already busted, I'm not too worryed about breaking it. I'll ponny up the 100 bucks for a used on from the big three and call it good, but I hate to replace something I might be able to fix. I have dreams that a mud dobber got into the AFM, buit a nest, and pluged up the by pass. This, I could fix.
The thing that bugs me, is I can't figure out why the by-pass, a simple tube around the barn door, with a screw at the end of it, has no effect on anything. If it was a bad vacume leak, I'd have a lean engine. If it was a bad set of fuel presure regulaters, I'd be able to move the mixture more rich, or leaner. If it was a bad temp sender, I should be able to move the mixture up or down with the by-pass, and the ECU should innore the O2 sensor. If it was a bad AFM, I should still be able to adjust the idle mixture up or down with the by-pass. If it was a bad throtal load swith, they wounld't work, and it would innore the O2 sensor. If it was a leaky cold start valve I should still be able to make the mixture leaner, or richer.
The only conclusion I can some to is something is counter adjusting for me moveing the by-pass screw, or something is preventing the by-pass from working.
You see why this is frustrating? I can't get the mixture to move, EXCEPT by induceing alought of false air.
So, since the bottem of the AFM is just bonded to the rest of the caseing, I remove as much goop as I can, and just press it up and out?
Thank you for bearing with me. I'm trying to give you as much information as I can, so you can maybe narrow it down, or see what I'm missing. I'm getting good are removeing 928 intake peices.
Thanks for the suggestion jpitman, I'll check them at the brain next. Even that wouldn't explain why the by-pass has no effect.
02-24-2003, 12:16 PM
#9
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Hate to tell you this, but it could be the brain. Not easy to check though. That's why I've been posting recently about an aftermarket ECU. I don't like being in the dark.
I've just been through a similar experience as you only to find out that it was in fact the brain (among some other little things).
I've just been through a similar experience as you only to find out that it was in fact the brain (among some other little things).
02-24-2003, 02:46 PM
#10
Instructor
VU,
AFM is easy to open. Use box cutter to carefully
cut the silicone seal around the lid and carefully
pry it off by applying steady pressure with a wide bladed instrument starting at the thin tapered end. Go around several times and eventually it will pop off.
Clean the ceramic contact area with alcohol. Mine was pretty dirty.
Also check voltage output from terminal 7 to ground while AFM is plugged in with ignition on. Should vary from around .75v with door closed to 6.5v with door fully open. This is easy to do with cover off-you can probe the terminal from the inside.
Joseph
'83 928 5 speed
AFM is easy to open. Use box cutter to carefully
cut the silicone seal around the lid and carefully
pry it off by applying steady pressure with a wide bladed instrument starting at the thin tapered end. Go around several times and eventually it will pop off.
Clean the ceramic contact area with alcohol. Mine was pretty dirty.
Also check voltage output from terminal 7 to ground while AFM is plugged in with ignition on. Should vary from around .75v with door closed to 6.5v with door fully open. This is easy to do with cover off-you can probe the terminal from the inside.
Joseph
'83 928 5 speed
02-24-2003, 05:12 PM
#13
Rennlist Member
Vibrus, didnt read all the posts, but what o2 sensor are you talking about? the kind that the service station will use ( wideband) or the voltage out of the 02 sensor thats on the car!!
(very inacurrate, not much change )Plus, the O2 sensor at idle will very its voltage up and down as part of the closed loop idle system. Idle switch has nothing to do with idle mixture, only off throttle fuel supply.
you will never get a change out of the stock o2 sensor, it is too crude.
as was said, your AFM is probably fine, check the voltages. turn on ignition, voltage should be 4.5 to 8 full flap deflected.
MK
(very inacurrate, not much change )Plus, the O2 sensor at idle will very its voltage up and down as part of the closed loop idle system. Idle switch has nothing to do with idle mixture, only off throttle fuel supply.
you will never get a change out of the stock o2 sensor, it is too crude.
as was said, your AFM is probably fine, check the voltages. turn on ignition, voltage should be 4.5 to 8 full flap deflected.
MK
02-24-2003, 05:31 PM
#14
Rennlist Member
Ok, just read all the posts.
1. with 02 sensor disconnected, your idle should go high
2. idle air C0 screw wont do anything measureable to your voltage output of the 02 sensor that comes with the car. dont even think of measuring that. It will go to a voltage of full rich, ie 13:1 or so, if the 02 sensor is disconected.
3. with fuel regs' vacuum disconnected, idle should go up.
4. idle should hunt with the 02 sensor connected and stablizes and go up with it disconnected.
5. timing should be around 10 degrees at idle.
6. the idle screw has no measureable effect on anything you can check, including part throttle or full throttle operation. however, you can measure your 70% part throttle switch. if you disconnect it, the voltage on the o2 sensor will go way lean at WOT, and 4-5krpms. The idle screw is just an air bypass to relieve pressure on the AFM flap to increase or decrease idle emissions, that are not meausureable by the 02 sensor. (very very small changes in mixture)
Im pretty familuar with the US sytem as I was able to get it to respond with all sorts of modifications. cams, headers, bigger displacement, fuel regs, etc.
ask away
MK
PS, check for false air , you cold be lean.
disconnect the idle switch for awhile, you dont need it and it will narrow down the variables.
1. with 02 sensor disconnected, your idle should go high
2. idle air C0 screw wont do anything measureable to your voltage output of the 02 sensor that comes with the car. dont even think of measuring that. It will go to a voltage of full rich, ie 13:1 or so, if the 02 sensor is disconected.
3. with fuel regs' vacuum disconnected, idle should go up.
4. idle should hunt with the 02 sensor connected and stablizes and go up with it disconnected.
5. timing should be around 10 degrees at idle.
6. the idle screw has no measureable effect on anything you can check, including part throttle or full throttle operation. however, you can measure your 70% part throttle switch. if you disconnect it, the voltage on the o2 sensor will go way lean at WOT, and 4-5krpms. The idle screw is just an air bypass to relieve pressure on the AFM flap to increase or decrease idle emissions, that are not meausureable by the 02 sensor. (very very small changes in mixture)
Im pretty familuar with the US sytem as I was able to get it to respond with all sorts of modifications. cams, headers, bigger displacement, fuel regs, etc.
ask away
MK
PS, check for false air , you cold be lean.
disconnect the idle switch for awhile, you dont need it and it will narrow down the variables.
02-24-2003, 05:36 PM
#15
Nordschleife Master
Thread Starter
OK, I've been trying to use the stock sensor.
When I disconnect the O2 sensor, the idle falls.
The fuel regs don't seem to have an effect. Bad regs? I'm getting a fuel rail pressure guage here shortly, and diagnose that.
The idle hunts all the time, and is much worse with the sensor disconnected. I tryed raiseing the idle with the sensor disconnected, she hunts a bit like that too.
The timeing is at 10 degrees advanced at idle.
Any clue why the idle falls, and the exaust realy smells of gasoline when the O2 is disconnected?
When I disconnect the O2 sensor, the idle falls.
The fuel regs don't seem to have an effect. Bad regs? I'm getting a fuel rail pressure guage here shortly, and diagnose that.
The idle hunts all the time, and is much worse with the sensor disconnected. I tryed raiseing the idle with the sensor disconnected, she hunts a bit like that too.
The timeing is at 10 degrees advanced at idle.
Any clue why the idle falls, and the exaust realy smells of gasoline when the O2 is disconnected?