'76 280Z Question on dist/manifold vacuum, dist timing, fuel pressure, brake booster

[Zed Head]

Yes, 68.7 ohms is continuity. That is about right for the heating element in the Air Regulator. I bought a new one for my car, because I accidentally pulled the heating element/bimetallic strip right out of the housing when trying to remove the connector, then I got a parts car, so now I have two extra.

I found that all three had around 60+ ohms of resistance and that they all worked after I cleaned up the valve inside (glued the first one back together). It get's gummed up like everything else in the intake system from backflow from the PCV system. You can move the valve back and forth with a small screwdriver, and spray it down with carb cleaner or WD40 or similar. You can also connect 12 volts directly to the two small terminals to confirm that the heater works, and the valve opens and closes correctly. But be very careful that you don't touch your clips at the connector contacts, it's tight.

As cozye said though, if it's closing when the engine warms up (there is actually a small heater block under it with engine water running through it) then it is a secondary problem.

[Jennys280Z]

Hey guys!

Cozye: On the ECU it's pin 6 to pin 8, 8 to 9, 7 to 8, and 6 to 7. But especially 6-8 and 8-9. I noticed that as I adjusted the wheel CCW, the numbers of the last two readouts increased ~2.5 ohms per "tooth" of adjustment while the first two stayed exactly the same (226 and 126).

I'll hold off on everything till the weekend and yup, I was thinking of checking the temp sensor after my car is fully warmed up since it's really a range reading and I can't tell as much with only one shoddy data point.

Zed: I was thinking the same thing earlier. I really don't want to pay $100 for this dumb thing and I was thinking earlier of just pulling it off and trying to clean it. I think there might be a decent chance I can fix it doing this, or at least get its performance better than what it is. I didn't know what the valve would look like or how much access to clean it I'd really have (I even thought of submerging it in WD40 for a few days if anything else).

I suspect my idle issue is separate from the way the car runs on the road however with this AFM the way it is, I don't know. I start the motor cold and it idles at around 800 for about 20-25 seconds and then it bogs down to 550RPM. Not slowly in stages but all at once. And warming up takes a lot longer at 550 than at 1300...although I can remember the bad thermostat days *shudders*

Yes it's closing when the engine warms up but it's only opening for 20-25 seconds and probably not as much as it should, if I can lay blame on this thing for at least my idle issues.

[Pomorza]

Hey guys!

I suspect my idle issue is separate from the way the car runs on the road however with this AFM the way it is, I don't know. I start the motor cold and it idles at around 800 for about 20-25 seconds and then it bogs down to 550RPM. Not slowly in stages but all at once. And warming up takes a lot longer at 550 than at 1300...although I can remember the bad thermostat days *shudders*

Yes it's closing when the engine warms up but it's only opening for 20-25 seconds and probably not as much as it should, if I can lay blame on this thing for at least my idle issues.

This describes my Z's idle the for the first couple of months I owned it. When it was chilly outside (or cold like it is today) I would start it and it would do pretty much the same the thing. I replaced the air regulator and it fixed right away. Personally I avoided fixing it as I thought it really didn't affect the cars driving (and I was not in the mood to spend $120). If you can live without it, it should be fine. I replaced my as it began bothering me on colds days when it would idle at ~500 for a rather lengthy period of time.

Hope that helps

Jan

Edited February 4, 2011 by Pomorza

[cozye]

If you really want to know about the air regulator, I suspect it's not opening fully which is why you get low idle.

Mine was doing this as well. I pulled the air regulator off and looked through the opening. It was open only very slightly, and not 1/3 of the way like the manual shows. I tried using carb cleaner to clean it, the shutter would move freely with a screw driver. It did close when the car warmed up and my idle would eventually climb to 800.

I didn't mind spending $100 on a new one and once I got the rest of the car running good I went on and purchased the new one. I noticed right away that the shutter was open much further on the new one.

Now my car idles at 1300 rpm cold and goes down when warm like it's supposed to. I suspect the spring on the inside weakens with age and doesn't open the shutter all the way. I figured it wasn't getting enough air because when the car was cold, I could pull a vacuum line off to introduce more unmetered air and the idle speed would increase which told me it wasn't getting enough air for the fuel that was being metered.

[Jennys280Z]

If you really want to know about the air regulator, I suspect it's not opening fully which is why you get low idle.

Mine was doing this as well. I pulled the air regulator off and looked through the opening. It was open only very slightly, and not 1/3 of the way like the manual shows. I tried using carb cleaner to clean it, the shutter would move freely with a screw driver. It did close when the car warmed up and my idle would eventually climb to 800.

I didn't mind spending $100 on a new one and once I got the rest of the car running good I went on and purchased the new one. I noticed right away that the shutter was open much further on the new one.

Now my car idles at 1300 rpm cold and goes down when warm like it's supposed to. I suspect the spring on the inside weakens with age and doesn't open the shutter all the way. I figured it wasn't getting enough air because when the car was cold, I could pull a vacuum line off to introduce more unmetered air and the idle speed would increase which told me it wasn't getting enough air for the fuel that was being metered.

Well I have my air regulator off at the moment and have been cleaning it and testing it, and you're telling MY story...everything I just noticed is how you said it. The plate isn't opening up enough when cold. It's not 1/3 of the way open like the FSM shows. More like 1/5 of the way open, if that. I've tried to clean it with carb cleaner and WD40. Mine closes fully when hot, which I tested just by running hot water over the case outside the heater. It sounds like based on your results, replacing mine doesn't sound like a bad idea.

I guess I could clean it, heat it and let it cool one more time to see if I see anything opening up any better, but if not, then maybe I should replace it. Having a good AR could make warmup problems a thing of the past. I took a look at the curves for the AR in the FSM. It's no longer functioning at all after 8 minutes or 180deg whichever comes first and it's a linear curve all the way down either way.

But then I wonder what your car was idling at cold before you replaced yours. Probably not the 550RPM that mine drops to.

I get about 800RPM for about 25 seconds and then a big drop to 550RPM. If the AR is not responsible for this sudden drop, then presuming I'll get 1300RPM from a new AR, I'd only drop to about 1050RPM due to whatever is causing my idle bog, which is still very healthy compared to what I've had.

But since it's not opening up all the way, I supppose this is the actual reason why I'm only getting 800. Why it only lasts for 30 seconds or less, I don't know. Maybe this would also be a symptom of the same weak spring.

It looks like I can take this thing apart btw. A glue blob keeping me away from a screw that keeps both halves of the casing together from the looks of it. Of course it's probably pressed or sealed with a lip or whatever but still, I've been tempted

As for the AFM if you test a 126/226 that's the only way at this point I won't send it in for replacement. So if you can still test yours this weekend let me know! I want to replace it since this is almost surely a case of Garbage-In Garbage-Out (ohmage to the ECU). I'll be driving a car with what I have to assume is a less-than ideal-shaped mixture curve and while I've "compensated for it", maybe I'll never be running 100% better until I do this. I'm trying to reconcile how my car runs with Zed's who said he had part-throttle issues when his AFM read like this. I suppose that could now be the case with my car as well, thinking back at how it drove on the road. I wondered theoretically if it's possible my car could run better at WOT now than with a new AFM...but I have to trust the folks at Nissan would have known how to set this thing ideally already.

Edited February 5, 2011 by Jennys280Z

[cozye]

mine was idling about 500-600rpm cold. It would barely idle without staling. I'm sure a new one will take care of your fast idle. But again, I can't stress enough that if it is closing it has absolutely no affect on how your car is running once warm.

You won't be able to get it to open further. Just plan on getting a new one. I ended up getting a nissan oem unit from MSA. Rock auto said there's was on back order.

[FastWoman]

Jenny, your big drop in RPM might have something to do with the cold start valve shutting off. I don't know how long it stays on, but it's an on/off sort of thing (and not gradual). You might try unplugging the heater on your air regulator and see if you still get that big drop at approximately the same time. If I'm right about your cold start valve being the doodad that's changing your idle, that would be another check mark in the "lean running" column.

Jenny, I've had a look at my 1978 FSM. There may be differences between our models, but the AFM and ECU should work approximately the same. Our FSMs also might be a bit different in the explanation given for how the AFM constructs the signal for the ECU. Mine says, "...the angle of rotation of the flap is monitored by a potentiometer provided inside as a potential difference U. A circuit diagram of the potentiometer is shown in Figure EF-13. When the flap deflects along with a change in the intake air flow rate, the terminal 7 mounted ot the flap shaft slides on the variable resistor R from R1 to R9, causing the voltage across terminals 7 and 8 to change. A constant voltage Ub (battery voltage) is applied across terminals 6 and 9. Then the air flow rate is converted into the voltage ratio signal U/Ub, which in turn is sent to the control unit for computation."

Anyway, given this explanation, it's indeed voltage ratios that are important to the ECU, not resistances.

Then I had a look at the mini-schematic of the AFM and your resistance measurements. You measure 74 Ohms resistance from 6-7, 200 Ohms from 7-8, and 226 Ohms from 6-8. The good news is that you're WRONG! Your measurements don't add up right. Your resistance from 6-8 should be the sum of your resistances from 6-7 and 7-8. And in fact you're reading on the high side.

Soo how would your measurements have come out this way? My guess is that you didn't get clean contact between your meter's probes and the terminals on your AFM, so you would have gotten added resistance at the junction between your probes and the terminals they were touching. This is a common problem for lower resistance readings. When you touch those terminals, you have to touch them very firmly. In fact most probes have pointed tips, and you should try to poke the point firmly into the metal, usually with the same pressure that you could apply to a #2 pencil point without breaking the lead. (That's not always possible.)

The other possibilities are that your meter is inaccurate or your probes are bad. When you touch the probe tips together, you should read zero Ohms. If you read some resistance above that, you can subtract that resistance off of any of your readings.

Anyway, I'm going to bet that you'll find something very different if you re-take your measurements with more pressure on the probes and/or cleaner contact points.

As for what you would NEED for your AFM to work properly.... Hmmmm....

The FSM only cites two measurements -- from 6-8 (180 Ohms) and from 8-9 (100 Ohms).

If I were laying out Nissan's diagnostic procedures, I think I would have used different measurement points. I'd have used the resistance values corresponding to U and Ub, namely 7-8 and 6-9, respectively. One can infer 6-9 as being 280 Ohms (an easy number to remember!). Then normal values could be established for 7-8 with the flap fully closed and fully open -- and even for points inbetween, marked on the potentiometer board itself. That would have been great. But that's not how they did it.

ANYWAY, what you need to compare to others is the ratio of your resistance from 7-8 and the resistance from 6-9 (which would correspond to the ratio of voltages U/Ub, which the ECU uses). Taking your measurements at face value, you've got 200 Ohms from 7-8 and 626 Ohms from 6-9. The resistance from 6-9 is (or should be) the sum of 6-8 and 8-9, which would be 352 Ohms. Your measured ratio is therefore 200/352 = 0.57.

Taking your 7-8 of 200, against the ideal total resistance of 280 Ohms, this ratio would be 200/280 = 0.71. However, again, your resistances don't add up correctly.

Anyway, the up-shot is that you might want to compare 7-8 with 6-9 on a known, correctly running AFM. I'd help you if I could, but my AFM might not be correct. (I've realigned the wiper position just a bit.) You need measurements off of a completely unmolested AFM on an engine known to run correctly -- probably from one of our friends in California or another emissions state (since those cars actually get sniffers shoved up their tailpipes).

And again, you need to re-take your measurements! They should all add up, give or take. So if you add up 6-7, 7-8, and 8-9, that should be the same as 6-9. If your margin of error is 5%, I'd say you're probably good.

Well, I HOPE that's good news. ;-)

Edited February 5, 2011 by FastWoman

[Zed Head]

I had a few more thoughts on how the AFM does its thing. They're just broad "can this thing work like it's supposed to" kind of thoughts.

126 is 26% higher than than 100. 226 is 26% higher than 180. So in percentage terms, the AFM being discussed is pretty far off. (In retrospect, this is why I bit the bullet and bought a reman).

180 - 100 =- 80 ohms (the ohm range for the factory settings on the AFM)

226 - 126 = 100 ohms (the range for the AFM being discussed)

The working range of the AFM is 25% wider, which would give a shallower enrichment curve (more vane movement required for the same relative change in resistance). So adjusting the vane spring would only get you back to "perfect" spec. if it also changed the slope of the enrichment curve.

The test that might be the most telling is the last one on page EF-51. Connect 12 volts to 9 and 6 and measure output at 7 and 8. Unfortunately, they don't tell what the values of the output should be, they just ask for smooth operation. It would be interesting to know what the upper and lower limits are though using a 12.6 volt battery. I might try it on my spare 1978 AFM.

IF you had the upper and lower output values expected for a certain voltage in, AFM closed vs. AFM wide open, then I think that you could be confident that your ECU is seeing what it's supposed to for a certain volume of air entering the engine.

Otherwise, it's still a guessing game. Just throwing some stuff out there while it felt clear in my head, plus for the mental exercise. It would be great if we could come up with an inexpensive fix or tuning procedure for this expensive part. If I get time, I'll put the results from that final test out here, just for reference.

[Jennys280Z]

mine was idling about 500-600rpm cold. It would barely idle without staling. I'm sure a new one will take care of your fast idle. But again, I can't stress enough that if it is closing it has absolutely no affect on how your car is running once warm.

You won't be able to get it to open further. Just plan on getting a new one. I ended up getting a nissan oem unit from MSA. Rock auto said there's was on back order.

Yup I thought they could order one in 4 days but when I tried to order it, it was a dead link.

Yup I know the AR won't help my car's running issues. If it was warm all year here I would put the old one back on and forget it. The way it is I dunno if I want to buy a new one or not. I took a picture of the valve fully open though. I hope this looks familiar. It looks like less than 1/3 to me but I will post a pic to see what you think.

On 2nd look, it is definitely open more than 25% of the way...probably 29-30% if I had to guesstimate.

Edited February 6, 2011 by Jennys280Z

[Jennys280Z]

Jenny, your big drop in RPM might have something to do with the cold start valve shutting off. I don't know how long it stays on, but it's an on/off sort of thing (and not gradual). You might try unplugging the heater on your air regulator and see if you still get that big drop at approximately the same time. If I'm right about your cold start valve being the doodad that's changing your idle, that would be another check mark in the "lean running" column.

Jenny, I've had a look at my 1978 FSM. There may be differences between our models, but the AFM and ECU should work approximately the same. Our FSMs also might be a bit different in the explanation given for how the AFM constructs the signal for the ECU. Mine says, "...the angle of rotation of the flap is monitored by a potentiometer provided inside as a potential difference U. A circuit diagram of the potentiometer is shown in Figure EF-13. When the flap deflects along with a change in the intake air flow rate, the terminal 7 mounted ot the flap shaft slides on the variable resistor R from R1 to R9, causing the voltage across terminals 7 and 8 to change. A constant voltage Ub (battery voltage) is applied across terminals 6 and 9. Then the air flow rate is converted into the voltage ratio signal U/Ub, which in turn is sent to the control unit for computation."

Anyway, given this explanation, it's indeed voltage ratios that are important to the ECU, not resistances.

Then I had a look at the mini-schematic of the AFM and your resistance measurements. You measure 74 Ohms resistance from 6-7, 200 Ohms from 7-8, and 226 Ohms from 6-8. The good news is that you're WRONG! Your measurements don't add up right. Your resistance from 6-8 should be the sum of your resistances from 6-7 and 7-8. And in fact you're reading on the high side.

Soo how would your measurements have come out this way? My guess is that you didn't get clean contact between your meter's probes and the terminals on your AFM, so you would have gotten added resistance at the junction between your probes and the terminals they were touching. This is a common problem for lower resistance readings. When you touch those terminals, you have to touch them very firmly. In fact most probes have pointed tips, and you should try to poke the point firmly into the metal, usually with the same pressure that you could apply to a #2 pencil point without breaking the lead. (That's not always possible.)

The other possibilities are that your meter is inaccurate or your probes are bad. When you touch the probe tips together, you should read zero Ohms. If you read some resistance above that, you can subtract that resistance off of any of your readings.

Anyway, I'm going to bet that you'll find something very different if you re-take your measurements with more pressure on the probes and/or cleaner contact points.

As for what you would NEED for your AFM to work properly.... Hmmmm....

The FSM only cites two measurements -- from 6-8 (180 Ohms) and from 8-9 (100 Ohms).

If I were laying out Nissan's diagnostic procedures, I think I would have used different measurement points. I'd have used the resistance values corresponding to U and Ub, namely 7-8 and 6-9, respectively. One can infer 6-9 as being 280 Ohms (an easy number to remember!). Then normal values could be established for 7-8 with the flap fully closed and fully open -- and even for points inbetween, marked on the potentiometer board itself. That would have been great. But that's not how they did it.

ANYWAY, what you need to compare to others is the ratio of your resistance from 7-8 and the resistance from 6-9 (which would correspond to the ratio of voltages U/Ub, which the ECU uses). Taking your measurements at face value, you've got 200 Ohms from 7-8 and 626 Ohms from 6-9. The resistance from 6-9 is (or should be) the sum of 6-8 and 8-9, which would be 352 Ohms. Your measured ratio is therefore 200/352 = 0.57.

Taking your 7-8 of 200, against the ideal total resistance of 280 Ohms, this ratio would be 200/280 = 0.71. However, again, your resistances don't add up correctly.

Anyway, the up-shot is that you might want to compare 7-8 with 6-9 on a known, correctly running AFM. I'd help you if I could, but my AFM might not be correct. (I've realigned the wiper position just a bit.) You need measurements off of a completely unmolested AFM on an engine known to run correctly -- probably from one of our friends in California or another emissions state (since those cars actually get sniffers shoved up their tailpipes).

And again, you need to re-take your measurements! They should all add up, give or take. So if you add up 6-7, 7-8, and 8-9, that should be the same as 6-9. If your margin of error is 5%, I'd say you're probably good.

Well, I HOPE that's good news. ;-)

AnthonyG's numbers don't add up either (see post #201) and I'll just say I'm positive I didn't measure it wrong. In fact I measured all of these values three times at three different times and got the same results every time. Using the probes works the same for every test so it would seem unlikely that I messed up the same one three times in a row. Resistance across the probes was zero or very nearly so. My multimeter was almost brand new at the time.

The 200 and the 75 figures change with the adjustment of the wheel. The 126 and 226 figures do not. I moved my wheel two teeth (~2.5) richer after cleaning and testing the AFM, and that 199 jumped to 206. The 73 increased 7 ohms to 80.

[Jennys280Z]

I had a few more thoughts on how the AFM does its thing. They're just broad "can this thing work like it's supposed to" kind of thoughts.

126 is 26% higher than than 100. 226 is 26% higher than 180. So in percentage terms, the AFM being discussed is pretty far off. (In retrospect, this is why I bit the bullet and bought a reman).

180 - 100 =- 80 ohms (the ohm range for the factory settings on the AFM)

226 - 126 = 100 ohms (the range for the AFM being discussed)

The working range of the AFM is 25% wider, which would give a shallower enrichment curve (more vane movement required for the same relative change in resistance). So adjusting the vane spring would only get you back to "perfect" spec. if it also changed the slope of the enrichment curve.

The test that might be the most telling is the last one on page EF-51. Connect 12 volts to 9 and 6 and measure output at 7 and 8. Unfortunately, they don't tell what the values of the output should be, they just ask for smooth operation. It would be interesting to know what the upper and lower limits are though using a 12.6 volt battery. I might try it on my spare 1978 AFM.

IF you had the upper and lower output values expected for a certain voltage in, AFM closed vs. AFM wide open, then I think that you could be confident that your ECU is seeing what it's supposed to for a certain volume of air entering the engine.

Otherwise, it's still a guessing game. Just throwing some stuff out there while it felt clear in my head, plus for the mental exercise. It would be great if we could come up with an inexpensive fix or tuning procedure for this expensive part. If I get time, I'll put the results from that final test out here, just for reference.

Looking at the lower value and the upper value as two static points the shift does seem to be the same. I punched that through a calculator myself when I tested at the ECU (old thread) and saw that equivalency.

I think the question is whether the entire curve is skewed exactly the same (25% increase across all points on the curve). I think this is unlikely because you noticed a difference at part-throttle but not at idle or WOT, and I would probably describe this to be the case with my car right now as well. Though leaning out the mixture even more than I already was has certainly made a difference for the better, I still notice something amiss at part throttle. Of course my idle is a disaster too but like cozye said, I think that's a separate issue however I won't rule out the AFM as possibly causing it.

I wanted to ask you if you remember anything that might have told you that you were running too rich before you replaced your AFM. I know about the part-throttle symptoms, but did you have any rich symptoms that you can remember?

Edited February 6, 2011 by Jennys280Z

[FastWoman]

AnthonyG's numbers don't add up either (see post #201) and I'll just say I'm positive I didn't measure it wrong. In fact I measured all of these values three times at three different times and got the same results every time. Using the probes works the same for every test so it would seem unlikely that I messed up the same one three times in a row. Resistance across the probes was zero or very nearly so. My multimeter was almost brand new at the time.

The 200 and the 75 figures change with the adjustment of the wheel. The 126 and 226 figures do not. I moved my wheel two teeth (~2.5) richer after cleaning and testing the AFM, and that 199 jumped to 206. The 73 increased 7 ohms to 80.

Jenny, all I can tell you is that the resistance of two resistances in series is the sum of those resistances. This is the gospel according to Ohm. Praise be to Ohm.

Seriously, I am dead certain on this. I couldn't be more certain. It's as basic as the question of how many money you would have if I gave you $3 and Eric gave you $2. You wouldn't have $6. Although I'm a neurobiologist by training, electronics has been a lifelong hobby. Furthermore, I went to a very prestigious college (in the company of thousands of other nerds like myself), and I sailed through freshman physics (where this was covered) easily within the top half a percent of the class. Electricity and magnitism was one of my favorite subjects. So I'm really, really quite certain! I promise!

Ah, but people on the internet can blow hot air. Lemme find something more authoritative for you...

Here you go.... From Wikipedia...

http://en.wikipedia.org/wiki/Series_resistance#Resistors

So if you believe me (and you really should), there's an error somewhere in your measurements. It might have to do with the measurement point. It could be, for instance, that there is extra resistance from corrosion in some internal connection in the AFM, perhaps from the potentiometer board to the backside of the connector (if that's where you're taking your measurements). Wherever it is, there's an error. That might be the source of your metering problems too, ya' know!

I'm just trying to save you some serious money.

Edited February 6, 2011 by FastWoman