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

[Jennys280Z]

OK, Jenny... So despite my best efforts to talk you out of it, you've decided to ditch your old AFM... Grrrrr... We'll keep our fingers crossed that this solves your remaining issues.

:bulb: So since you've gone and ordered the thing, it would really be great to glean some calibration points off of it. If you could take some basic measurements on the thing (with the cover left intact over the potentiometer assembly, thus not voiding your warranty), I think I could develop those measurements into a complete and more refined diagnostic and calibration procedure, using my '82 AFM as a reference.

I'm thinking you could power the thing off of a 9V battery with alligator clips (a very safe method -- the way I suggested before) and take voltage measurements at reproduceable flap openings. You could also measure the spring tension per Atlantic Z's beer can method. (Even better, you could use a centigram or milligram scale if you have one.)

Could I talk you into doing this? Please, please? :classic:

With regard to the CTS, it is out of spec, isn't it? It's on the high side, which could be running your engine a bit richer than you would want. These CTSs are hugely important for establishing the right mix -- second only to the AFM. Anyway, yes, you can lower the resistance of the assembly with a simple fixed resistor in parallel, rather than a second CTS. A fixed resistor would be fine for a little tweak, but you could lose temp compensation sensitivity if you have to make bigger changes. In that case (bigger changes), a second CTS in parallel would retain the sensitivity. (Or so goes my theory.)

But let's hope the new AFM solves your issues.

I was out of the resistance range at 50degrees, yes. Until yesterday I was going to test the CTS at the ECU at 176degrees which would show me that it's botching the mix when the engine is hot too, but perhaps being out of spec at a single temperature is good enough, good enough to replace a $13 part. x

Well to do the mechanical tests with the spring tension like I did with my AFMs here, I'll need inside that cover. Of course I'll do the electrical tests with the ohmmeter. If I don't get a 180/100 combo plan obviously I'm going to be distraught and will need morale support here from y'all

Another thing that's been bothering me too is the thought of replacing the CTS without the AFM and leaving my AFM wheel where it is. I'm tempting a frontfire I just know it...women's intuition...something tells me to wait on the CTS until the AFM is here and install them both at the same time. All just a newbie going on nothing but theory and a hunch, as always. :classic:

[FastWoman]

I had a different spring tension test in mind. I'm interested in the force required to just start opening the flap. I'm also interested in the voltage output at different flap opening distances, which you could determine by pulling the flap open with a string in perhaps 1 cm increments (e.g. marked on the string). No need to open the cover for any of that.

Can I mail you the stuff you'd need for powering the thing up with a 9V battery and testing voltages?

*9V battery

*9V battery clip with alligator clips on the leads

*a couple of test leads with alligator clips on their ends

Just to be clear, the 9V battery isn't going to put out anywhere near enough current to hurt anything, even if you accidentally short your leads.

I know you think the resistances are more important than the voltages, but if you could humor me on this test, I think we could put together some really good test/calibration procedures for use by the Z community. Among other things, you and I could use it to test/calibrate our spare AFMs.

re your intuition about replacing the CTS before the AFM: Go with your gut!

[Jennys280Z]

I'm too scared to do that, FastWoman. I barely trust myself just to install the thing and cross my fingers it works (or even that my car runs better than it does now and not worse). If you were here I would let you do it. But for posterity sake, I will consider taking it off and testing it properly (12V should probably be used for a benchmark) AFTER using it for over a year.

But no, I don't want to install my CTS first which I could have done tonight. I got the CTS in my hand but I won't dare install it without the AFM at the same time.

[FastWoman]

OK, I understand, and that's fine. You shouldn't do things that are past your comfort zone.

Well, a year or so down the line, if you happen to have the thing off your car, and IF you're comfortable with it then, please shoot me a PM, and we'll work on a calibration procedure.

The offer/request also stands for anyone else who has a "virgin" (or nearly "virgin") AFM. (Zed????)

[Zed Head]

I'll see if I can come up with at least a one or two point calibration number using a 9 volt battery. Maybe a fishing weight or similar hanging on the vane. My beer comes in bottles. The hard part in these situations is coming up with something reproducible. Using common coins as weights might work.

[FastWoman]

Zed, thanks! My thought is that the following could be used to calibrate and verify an AFM:

Spring tension: Force needed to open the flap just far enough to close the fuel pump cutoff switch (or to just open the flap if there's no fuel pump shutoff switch.

Voltages: Full closed, full open, and perhaps some reproducible increments inbetween. Perhaps this could be done by measuring distances the flap is deflected. There are certainly some landmarks on the potentiometer board that could be used if one is to open up the AFM cover. However, I'm wondering whether it could be done accurately without even opening the cover -- maybe by marking increments on a monofilament line with a sharpie. Or maybe the increments could correspond to the landmarks on the potentiometer board.

Your idea of using coins is good, except for our friends in other countries! Even aluminum cans differ between countries.

Anyway it would be great to make this work. There are so many people questioning their AFMs, and it would be great to have a better method for making certain everything is up to snuff.

[Zed Head]

A flow bench would be the best way, considering the application. I wonder how the rebuild guys do it. There is leakage past the vane, plus the offset from the air idle circuit.

I found that my rebuilt AFM had enough air going through without moving the vane that, after advancing my timing, I had to adjust the fuel pump cutoff switch to only work when the vane was just barely open. The engine almost had enough air through the idle circuit and leakage to run without any vane contribution. The idle air circuit will change the liftoff point of the vane, I used it to keep my fuel pump switch from cutting off for a little while. I had to lean the idle air back out for Oregon emissions though (eventually I just bent the fuel cutoff switch arm to make it work).

I already tried a few things with a roll of quarters on top of the vane but the only way to be reproducible, in my opinion, is to hang a thread from the edge of the vane, so that the lever arm length is consistent. Basically, I ended up where atlanticz did. But I think that one measurement, with the vane perpendicular or midway, is all you would need since you can't change the spring constant (edit - actually, maybe you can, with the other screws inside the AFM, I haven't been that deep) and you can only change the preload by rotating the wheel.

I would say that using atlanticz's method of attaching the weight, but using a known reproducible weight (rather than pop cans and water), hanging that weight and measuring the voltage ratio, volts in at 6 and 9 vs. volts across 7 and 8, would give you the best calibration number to try and match. (second edit - the main purpose of this exercise is to compare AFMs, voltages to the ECU, I think, known good ones vs. others).

I'll go hang a known number of quarters from the vane and measure the voltages. That's really the best it will get without a flow bench, I think.

Edited February 18, 2011 by Zed Head

[Zed Head]

Here is a single mid-vane data point if anyone ever has the urge to see where their AFM falls in comparison.

1978 AFM

9.62 volts across pins 9 and 6

Output measured at pins 7 and 8

AFM bore pointed down and leveled

Mid-vane measurement taken with a taped roll of 28 quarters hanging by a thread from the edge of the vane.

Vane Closed 4.74 volts (49 % of input)

Vane Open 0.12 volts (1.2 % of input)

28 quarters 0.488 volts (5.1 % of input)

The first two measurements tell about the potentiometer and the last one tells about the spring tension. The vane was only partially open with 28 quarters hanging from it. I tried 20 quarters but the thread rubbed on the housing and I could not get a consistent number.

I have attached a picture so that you can see how far open the vane is with only 5.1 % of the input voltage going to the ECU.

This might seem like some nonsense but it's pretty interesting. If you consider that the ECU is also using small resistance readings fromthe various temperature sensors also, it's easy to see how things can go wrong.

Note that this AFM ran well on a parked car, and had normal (100 and 180) resistance readings but I have not actually used it under load. Except for starting the car in gear on jack stands and applying the parking brake while the wheels were turning, to test it. It sounded good.

Fun, fun, fun...

[FastWoman]

Zed, I really like your idea of volts against quarters! Here's my thought: Use pennies instead. They're ligher, and people generally have more of them sitting around. But otherwise, yes, great idea!

It makes sense to me that the AFM is designed to be just leaky enough to pass idle air without (much) movement of the vane. It makes no sense to have the AFM sensitive to sub-idle air flow. That would explain (to me) why the vane would be designed to be under tension even when fully closed.

I think the spring constant CAN change. The metallic properties of the spring might change over the years, and I suppose the thing could even rust. What would change the spring constant would be the length of free spring between the two attachment points. In fact this is how mechanical clocks/watches are regulated. So I suppose the first thing is to get the just-opening and full-open tensions right. Then the voltage/pennies curve could be measured from there.

I'm going to go grab my '82 AFM and have a look...

[FastWoman]

So here's my setup for spring tension:

1 sheet of 20 lb copy paper, folded up into a cup, with 3 staples securing it.

1 short length of string taped to the flap

AFM with air outlet facing down, sitting on level table

22 pennies will just open the flap (on my seemingly unmolested '82 N/A ZX AFM

28 pennies will open the flap approx parallel to the table

238 pennies will open the flap fully

I'd try quarters, but I don't have many.

Notes: My pennies are 2.56 g each, and my paper/3-staple/string rig is 4.93 g (approx. a 2 penny equivalent).

I'll try voltages next.

[FastWoman]

BTW, there is no way on this '82 AFM to adjust the spring constant. The ends of the clock spring seem to be molded into the plastic parts.

[Jennys280Z]

Isn't it possible that we could "bump into" the right people working for some of these remanufacturers and steal the secret formula?

At the very least, to have the baseline from which to Dx the car.

I just drove my car again...first time since last time I wrote about it. My idle was no more than 900RPM even with the AR looking the way it is. However, the car held that higher idle speed for a lot longer than the 20-25 seconds that it was. So it seems plausible that my AR is fully functioning now and something else is still affecting my idle (900RPM when I should be 1400+?!).

I swear this damn car is like a different car every time I drive it.

On the road the car backfired a dozen times out the tailpipe when letting off the throttle during the course of the 20 minute drive. I smelled exhaust sometimes and sometimes not. Most noticeable about this drive was how herky jerky the motor felt this time. The motor looked like it was shaking while still warming up, like it was shivering. I thought I heard some kind of breathing sound and I'm worried that my main problem might be a blown intake gasket. I sniffed the heck out of it and couldn't find any vacuum leaks on the top of the gasket.

But what about the bottom of the gasket??? Would a hole in the bottom of the gasket be the kind of thing to put my vacuum at 14-15, cause wacko problems with my mixture, maybe even cause different mixtures in different cylinders?

FastWoman I know you had this issue before and I've tried to put it out of my mind. Anyway I will probably go to a mechanic if it's an intake manifold issue. Maybe I'll get him to slap on a new exhaust gasket too if he tells me he has to take the exhaust off first.

Now that everyone is bored from reading my rant, and wishing they had their two minutes back, here is the question: How do I test for a vacuum leak under this bedamned intake shield? Is it safe for me to get loose and funky with the carb cleaner down there? Has anyone tried seeing underneath it with mirrors/lights (periscope) or camera? I figure if the mist is fine enough just getting the carb cleaner in the air in the vicinity of the gasket's bottom is enough, right?

I don't own a good fire extinguisher yet. And my floorjack is like...old. Does anyone have a low-cost recommendation for fire extinguishers and/or a new jack for my car?

Edited February 19, 2011 by Jennys280Z