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

[cozye]

That pic looks like it is opening more. Give it a shot.

Zed, read my previous post to her. Mine was closing consistently, however it was not opening far enough to get proper air on warm up, would idle very low until ECU dropped the cold start enrichment. I could pull a vacuum line off and the idle would kick up 300 rpms. New AR fixed it and now idles perfectly on warm up. I did try cleaning mine but it didn't work.

[FastWoman]

Jenny, I'll have to give my own air regulator the same "shake, rattle and roll" treatment. Maybe I'll get a higher cold idle.

It might be worth trying something on your AFM. I suspect you could substitute new fixed resistors for R0 and R10. You can cut foil traces on the potentiometer board with a razor knife, and you can solder to them (very carefully) by scraping the lacquer off of the top of the remaining foil trace. You can surface-solder by laying the tip of a new resistor atop the scraped foil trace and applying solder sparingly. Then you can solder the other end of the resistor to the AFM's connector. I suppose this would be major open-AFM surgery! Resistors are cheap, and you can buy them at your local Radio Shack. And if you can't, I'd be happy to mail you whatever you need.

You can both check and clean a CSV with an air compressor. Do you have one? Just connect up a hose, and pressurize the thing with 30 or 40 psi of air. It will drip or hiss for you if it's leaking. Then pass 12V through the connector to open it. Mine makes a nice click when I do this. To clean it, fill the hose with some Chemtool B12 solvent, and pressurize a bit into the valve. Let it soak for a while, and then shoot it out under air pressure. You should see a nice, wide spray pattern, and again the valve should hold pressure when you de-energize it. FAIW, the CSV on my engine was sluggish and would occasionall stick partially open. This cleaning method did remedy the problem. Just to be safe, though, I kept it as a spare and transplanted my spare, cleaned-up CSV from a ZX intake.

[Jennys280Z]

Jenny, I'll have to give my own air regulator the same "shake, rattle and roll" treatment. Maybe I'll get a higher cold idle.

It might be worth trying something on your AFM. I suspect you could substitute new fixed resistors for R0 and R10. You can cut foil traces on the potentiometer board with a razor knife, and you can solder to them (very carefully) by scraping the lacquer off of the top of the remaining foil trace. You can surface-solder by laying the tip of a new resistor atop the scraped foil trace and applying solder sparingly. Then you can solder the other end of the resistor to the AFM's connector. I suppose this would be major open-AFM surgery! Resistors are cheap, and you can buy them at your local Radio Shack. And if you can't, I'd be happy to mail you whatever you need.

You can both check and clean a CSV with an air compressor. Do you have one? Just connect up a hose, and pressurize the thing with 30 or 40 psi of air. It will drip or hiss for you if it's leaking. Then pass 12V through the connector to open it. Mine makes a nice click when I do this. To clean it, fill the hose with some Chemtool B12 solvent, and pressurize a bit into the valve. Let it soak for a while, and then shoot it out under air pressure. You should see a nice, wide spray pattern, and again the valve should hold pressure when you de-energize it. FAIW, the CSV on my engine was sluggish and would occasionall stick partially open. This cleaning method did remedy the problem. Just to be safe, though, I kept it as a spare and transplanted my spare, cleaned-up CSV from a ZX intake.

Can you come over and help me solder the resistors? I can scribble on a schematic. I would need your help to actually DO anything!

R10 looks easy enough to do (in theory) but what about the desired resistance value of R0?

I just wonder about the point that Zed made, if this shift of 25% (which Zed noted a range is also increased about 25%) reshaped my mixture curve at all? If it didn't and my curve is parallel to the original curve, then the adjustment at the wheel should move me over to the point I should be and result in a 100% fix.

Good advice on the CSV! Thank you so much!

Despite the promising look to the pictures...I have a feeling this isn't going to be much of a fix. It seems like my valve closes too quickly/easily. Just from the heat of my hand holding the part while cleaning it? I knew I was hot but not that hot

Just based on tinkering with the AR, it seems like I can get it to open like that after manipulating it with a screwdriver, but when it starts to close from handling/cleaning it didn't seem to reopen all the way till the screwdriver...anyway it was worth a shot. I did shake particles of grime out of it, FWIW. I wonder if I'll see above 1000RPM at least the first time I start the car...will know hopefully tomorrow. LY guys

Edited February 12, 2011 by Jennys280Z

[Jennys280Z]

I live in the south which is one of the reasons why I'm not going to replace my AR. If I lived in New York or Ohio I would have swapped it out for a new one I'm just not going to drive my car in the cold anymore! That ought to take care of more than half of my AR problems right there.

Yes it's winter right now, but it's going to be over 60degF here tomorrow and sunny. Perfect drivin' weather! xx

[FastWoman]

Jenny, it's easy to surface-solder. See if you can find some junk piece of electronic equipment around that is destined for the trash. Pull out a PC board and practice on that. You'll find it's pretty easy. You can get a soldering iron (probably 30 or 40 watt) and some rosin core solder at Radio Shack. General soldering instructions can be found on youtube.

If you want, I can measure R0, R of the potentiometer, and R10 off of my spare AFM, which is off of an '82 ZX. I'd hate to open up the AFM on my car, though, as it'd make a huge mess. Besides that, the AFM *might* have very minor issues.

Before you get into that song and dance, though, you might want to check your voltages with the AFM full-closed and full-open, so that you can compare them to Zed's. You don't need to power the AFM off of your car battery, if that makes you nervous. (I admit it'd make me a bit nervous too. I bench tested my AFM with a regulated power supply that was current-limited to 1A.) You might pick up a battery clip of some sort at Radio Shack. It doesn't matter what type. The cheapest would probably be a 9V battery clip. Solder a couple of alligator clips onto the wires. When powering the thing off of a little 9V battery, you won't have to worry about blowing anything up. Then just consider all your voltages in proportion to the supply voltage (roughly 9V, which you should measure while the battery is under load). All of your voltages should be proportional to Zed's.

Finally, even if your AFM is slightly askew, you can probably still use it. All you need is the proper mechanical properties (spring tension) and a smoothly working potentiometer that won't send "jumpy" readings to the ECU. You can compensate for any errors in the AFM by altering the coolant temp circuit's resistance. I don't know if it's in your '76 FSM, but my '78 FSM states that this resistance determines the multiplier used on the duration of the injector pulse across all operating conditions (or words to that effect). Your mix might not be perfect across all conditions with this tweak, but it will be pretty close -- certainly as close as anything else on this primitive EFI system.

[Zed Head]

While I remember, and in case you come across one - I have found that my spare 1978 AFM is mechanically identical to my 1976. It even has the working fuel pump contact switch, even though, according the FSM, the pins connecting to it are "useless."

Having worked in manufacturing, it may be that the company gave the same part a new number, during a transition. Later products might not have the switch. Something to consider if you came across a 1978 AFM for cheap. Check for the fuel pump contacts and it might work on your car. My spare 1978 AFM has the Datsun factory label on it, so does not appear to be a reman.

But, and I hate to muddy up a muddy situation, there is also the outside possibility that the 1978 has a different spring tension than the 1976. I would be surprised if this was the case but since there is little information on the factory spring tensions, it is a possibility.

If we get a few rainy days here I might connect my shop vac to both AFMs and see if the voltages are the same, at the same air flow volume.

1976 is A31-060-001

1978 is A31-604-000

We will be building new parts from scratch by the time we're done here....

[Jennys280Z]

Jenny, it's easy to surface-solder. See if you can find some junk piece of electronic equipment around that is destined for the trash. Pull out a PC board and practice on that. You'll find it's pretty easy. You can get a soldering iron (probably 30 or 40 watt) and some rosin core solder at Radio Shack. General soldering instructions can be found on youtube.

If you want, I can measure R0, R of the potentiometer, and R10 off of my spare AFM, which is off of an '82 ZX. I'd hate to open up the AFM on my car, though, as it'd make a huge mess. Besides that, the AFM *might* have very minor issues.

Before you get into that song and dance, though, you might want to check your voltages with the AFM full-closed and full-open, so that you can compare them to Zed's. You don't need to power the AFM off of your car battery, if that makes you nervous. (I admit it'd make me a bit nervous too. I bench tested my AFM with a regulated power supply that was current-limited to 1A.) You might pick up a battery clip of some sort at Radio Shack. It doesn't matter what type. The cheapest would probably be a 9V battery clip. Solder a couple of alligator clips onto the wires. When powering the thing off of a little 9V battery, you won't have to worry about blowing anything up. Then just consider all your voltages in proportion to the supply voltage (roughly 9V, which you should measure while the battery is under load). All of your voltages should be proportional to Zed's.

Finally, even if your AFM is slightly askew, you can probably still use it. All you need is the proper mechanical properties (spring tension) and a smoothly working potentiometer that won't send "jumpy" readings to the ECU. You can compensate for any errors in the AFM by altering the coolant temp circuit's resistance. I don't know if it's in your '76 FSM, but my '78 FSM states that this resistance determines the multiplier used on the duration of the injector pulse across all operating conditions (or words to that effect). Your mix might not be perfect across all conditions with this tweak, but it will be pretty close -- certainly as close as anything else on this primitive EFI system.

I'm skeered. I do have old boards of all kinds so that wouldn't be a problem.

For adding resistance to my coolant temp sensing circuit, that is enriching the mixture I would think. My resistance at 50degF air temperature was a bit high (4500 ohms vs. 3250-4150). I hope that my reading at 180degF will be in line but it might be too high as well. Will such high results mean that I should replace my CTS and that is the likely culprit in funking up my mixture?

[Jennys280Z]

While I remember, and in case you come across one - I have found that my spare 1978 AFM is mechanically identical to my 1976. It even has the working fuel pump contact switch, even though, according the FSM, the pins connecting to it are "useless."

Having worked in manufacturing, it may be that the company gave the same part a new number, during a transition. Later products might not have the switch. Something to consider if you came across a 1978 AFM for cheap. Check for the fuel pump contacts and it might work on your car. My spare 1978 AFM has the Datsun factory label on it, so does not appear to be a reman.

But, and I hate to muddy up a muddy situation, there is also the outside possibility that the 1978 has a different spring tension than the 1976. I would be surprised if this was the case but since there is little information on the factory spring tensions, it is a possibility.

If we get a few rainy days here I might connect my shop vac to both AFMs and see if the voltages are the same, at the same air flow volume.

1976 is A31-060-001

1978 is A31-604-000

We will be building new parts from scratch by the time we're done here....

Hehe I will send the blueprints to the machine shop tomorrow morning.

That'd be the big daddy of all AFM tests if you could do that with a shop vac.

Yup I definitely have two 1976 AFMs that are physically identical and have the exact same readings. GRRR

[FastWoman]

Jenny, if your CTS is out of spec, I'd replace it anyway. It's not a very expensive item. Unfortunately it's a bit hard to get a wrench around, but mine wasn't very hard to remove (not corroded in place). I did end up removing the thermo housing from the side of the head to give me access for removing an exhaust manifold stud, so it was much easier for me to access the CTS. In hindsight, it's probably a good idea to remove the thermo housing every now and then anyway, to keep the bolt threads clean and workable. The gasket is quite cheap.

If you do need to alter the CTS circuit resistance, remember that you can either increase the total resistance by adding resistance in series (richening the mix) or decrease the total resistance by adding resistance in parallel (leaning the mix). In fact if you needed to cut the resistance in half, you could probably use that un-used threaded hole in the thermo housing for a second CTS, to be wired in parallel. There are options available. We just haven't figured out what you need to do yet.

Zed, that's a cool idea about using a shop vac. I wonder whether there would be some way to standardize that.

It would be great if we could develop more accurate calibration methods for our AFMs. It might be a worthwhile project for us, collectively.

FAIW, the Atlantic Z beer can article talked about two different years of AFMs that supposedly had the same spring tension (testing unmolested units). I think one of them was even from a ZX.

[Jennys280Z]

Jenny, if your CTS is out of spec, I'd replace it anyway. It's not a very expensive item. Unfortunately it's a bit hard to get a wrench around, but mine wasn't very hard to remove (not corroded in place). I did end up removing the thermo housing from the side of the head to give me access for removing an exhaust manifold stud, so it was much easier for me to access the CTS. In hindsight, it's probably a good idea to remove the thermo housing every now and then anyway, to keep the bolt threads clean and workable. The gasket is quite cheap.

If you do need to alter the CTS circuit resistance, remember that you can either increase the total resistance by adding resistance in series (richening the mix) or decrease the total resistance by adding resistance in parallel (leaning the mix). In fact if you needed to cut the resistance in half, you could probably use that un-used threaded hole in the thermo housing for a second CTS, to be wired in parallel. There are options available. We just haven't figured out what you need to do yet.

Interesting idea!

Is there an easier way to run parallel than with a 2nd CTS?

Yes I don't know what my car's problem is yet with running rich. I'm considering walking the AFM wheel another half-tooth to full tooth richer than where I am now because I don't want to wind up too lean from fixing something and then risk backfiring out my intake, and I have a feeling that would make a better mixture compared to where I am now.

Did you mean in your first paragraph that I should replace my CTS even if it's not out of spec? If that's what you meant then I'll just buy one and replace it. I looked at it and noticed how hard it is to get a wrench in there. Rut ro! It's all green too like an old copper statue in E.Europe.

Edited February 14, 2011 by Jennys280Z

[Jennys280Z]

Okay I just splurged on a new AFM and CTS.

What kind of wrench is best to take off the CTS? I sprayed some Kroil on it a week ago anticipating taking it off to test it. It's been replaced once on my car in 35 years. I figure since it's only $16 including shipping I might as well slap it on at the same time as my new AFM.

[FastWoman]

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.

Edited February 14, 2011 by FastWoman