I have a 76 280z that runs rough, lacks power, and is quite gas-inefficient. I checked my air temp sensor and water temp sensor w/ a multimeter, and they read acceptably. I hooked up a vacuum gauge with a T at the FPR vac line, and these were the results:

~10.5 in Hg @ 800 rpm (not jumpy, but twitchy)

(I don't have a tachometer yet, sorry)

drops to ~4.5 in as throttle is applied

raises back to ~10 in to WOT

up to ~20 in @ throttle release

Fuel pressure (gauge is not very accurate)

39 psi (idle)- 42/43 psi (throttle applied)

I tried messing with the AFM (PO put wrong one on the car)- gave it more fuel while also decreasing idle back to 800 rpm (my dad was screaming the tach reading to me over the exhaust hahaha) and my vacuum started drifting steadily between 15-17 inches, which would be more acceptable.

I don't have any big irregularities except for the fact that the vacuum is SO LOW, and I understand that is causing my very high fuel pressure.

I checked my valve timing, I cranked the crank pulley till the timing mark was at 0 deg BTDC, so TDC.

Weird side note: my intake/exhaust cam lobes were making 11:15, if the intake were the hour hand and exhaust was the minute hand (relative to timing chain). Also the dizzy was pointing underneath the upper radiator hose, looked as if it were already touching the #1 plug wire contact. That don't seem right.

So anyways, I looked to the marks on the cam sprocket, and the triangle was waaaay to the EDIT**right of the mark. So I'm too advanced, I wonder how that happened.

Then I decided to look at my PCV valve, so I popped off the hose under the BCDD going to the intake manifold, nothing there! Just a bunch of carbon. Whaatt? I need a PCV valve.

SOO, I've gathered I need to adjust my valve timing, and the right model AFM would help too, yeah? What do you guys gather from this? Thanks a bunch for any input!

Edited August 17, 201113 yr by ll77

My gauge finally came in today, and I bought the proper fittings for it (although it will be a bit awkward). I'm really swamped with homework right now, school started last week. But I'll probably have time to put it on over the weekend. Or I might wait until the AFM comes in, which should be really soon. We'll see. I'll definitely keep posting! I am still very determined!

Fuel prssure reading is here! I put on a stock ignition coil today (replaced an MSD that came on the car, I heard it could cause misfires). I put on the gauge with an elbow fitting, and it leaked gas from the fitting. I did get a reading (maybe it was lowered because of the leak?), 30 psi at idle, ~36 revving. That's normal right? I then took the gauge off and tried to tighten it onto the fitting more, and the white gauge face on the inside bent. I've tightened to the point where I can't possibly tighten anymore without a vice. I even rounded the fitting a bit. But now it won't twist on because the gauge is in the way of me twisting it onto the T on the feed line, but I think this reading will suffice, right? I think I'll just take my time on the gauge for now, unless you guys need another reading.

I've replaced the vacuum lines, and I soldered my injector pigtails on, but I haven't been very productive on my car lately. I'm still waiting on the AFM, which should arrive any day now. More updates soon.

Edited September 5, 201113 yr by ll77

Your pressure sounds normal. The differential between your revving and idling psi is sort of low, suggesting that your engine vacuum is low. Of course it's a bit hard to tell from a fuel pressure gauge.

When screwing NPT-type fittings together, it's good to wrap the thread with teflon tape to lubricate and make a good seal. You might be able to take the gauge apart to fix the bent face.

I think getting the right AFM on your car will be a good step forward!

Yes, I am really looking forward to its arrival! And I got it at a great price off a HybridZ fellow. I have heard something of teflon tape, but since the old gauge didn't have any, I didn't think it was necessary. I thought perhaps it was mostly for water plumbing situations. Now that fitting is on so freaking tight, I'm probably going to have a hell of a time taking it off and putting some on. Sucks!

And yeah I thought of taking it apart too, but it seems I'll have to figure out some way to pry the front plastic covering off. It's got a metal shroud around it and it seems to be pressed on. I'm afraid if I take it off, it'll never fit like it does now. This gauge stuff is getting on my nerves! Oh well, it'll be fun to find out how it works. Keep you posted!

Hello once again. The "correct" AFM came in today, but I fit it on, and now she won't run. Starts up fine, then sputters and dies in a few seconds. I've seen a thread that describes this exact problem after changing AFMs, but I've spent the past 4 hours looking, and I swear I couldn't find it if my life depended on it.

I was thinking that other things had been used to compensate, so I messed around with the ignition timing, the idle speed screw and even manually pushed the AFM counterweight around, none of these helped. The guy I bought it off of said it ran real swell on his car (another 76 280z), and he seems like a legit kind of guy. What else should I try?

Oh yes, and my car ran the same way it did this morning, it only acted this way after the switch. I didn't mess with anything else today other than the AFM. Please help, if there has ever been a time I've needed help, it is now! Thank you!

Well, you might want to start simply by comparing the two AFMs. Does the flap open much more easily on one than the other? Are the resistances remarkably different?

I'm going to make a guess here: Maybe your fuel pump shutoff switch isn't quite right, so your fuel pump is running when you turn the key to "start," but not running thereafter. I think the '76 models use a fuel pump shutoff switch found on the vane-closed end of the potentiometer assembly. This switch is preserved in later models, but not connected, and then the switch is missing altogether in still later models. If '76 is one of those shutoff switch years (pretty certain it is), make sure that (1) your new AFM actually has the switch, and (2) it's adjusted so that the switch contact actually closes when you fire up the engine.

FastWoman is right, the AFM's for 1976 came with the fuel switch in them and your symptoms sound like yours is not working. The switch is bypassed during Starting, but comes in to play when the key is at On. So if the switch doesn't work, the pump will turn off when you let go of the key. The engine then runs until fuel pressure drops.

It's odd though, that the engine ran with the other AFM, since it probably would not have had the switch if it was the wrong one. There were only a few years that used it, and I think that they all were the same AFM model. What are the AFM numbers?

There are pictures on the atlanticz site of the switch. It's under the black cover. You can bend the rod that moves the switch to make it work correctly, if that's the problem. http://atlanticz.ca/zclub/techtips/afm/index.html

Oh, yes the first thing I did was push the flap in, it opened an closed real smooth, but I'll run through the multimeter tests today. One difference I noted (probably not a big deal) is that the new, "correct" one has what I believe is a circular valve of some sort on the flap, to open up for frontfire perhaps.

I'm sorry, I'm afraid I've never been too great at electricity. When you say the contact is closed, does that mean the contacts are not touching? I have cracked open the cover, and the switch is intact, and compared to the other AFM, nothing looks off about it. Also, Zed Head, are you saying that upon start up, the contacts touch but the switch is bypassed, then when the key is in "on" the contacts don't touch? If so, I have manually kept the contacts from touching because my reasoning was that once they touch, the fuel pump stops, but same deal.

Oh yes, something possibly worth mentioning, there's all this turquoise-green crap under the cover where the connector is. Looks a bit like old battery acid, but turquoise. It's even on the cover, looks like it's splashed on, only in the general area of the connector. Strange.

I'll update you guys w/ multimeter test results when I can, thanks.

Edited September 11, 201113 yr by ll77

Ok, all the multimeter tests as described in the FSM check out. As far as I can tell, the results are identical to my mismatched one. Hmmm..

Edit: Ahhh, I see what you're talking about now. The switch has 2 contacts located at the base of the connector. They are the 2 left most contacts, yes? So at the "on" position, these 2 contacts are closed, when there is no air passing through, the arm disconnects these 2 contacts; they are "open." Ok, I get it now. And yes, the contacts do close when the arm doesn't touch the contact.

Also I checked resistance between all kinds of contacts under the cover, resistance is identical to my other one. Seems to be a good functioning air flow meter.

Oh yes, another thing worth mentioning, the glue blobs are intact.

So in the end, the only thing that don't sit right with the new AFM is the turquoise stuff. I can tell it was liquid at one point, it looks to have pooled up at the bottom of the cover. Now how the hell did liquid get in there?

Edited September 11, 201113 yr by ll77

Another update, I slapped on the AFM once again, and it worked. It stayed running. Maybe the connection was loose yesterday, despite the fact that I had unplugged and replugged numerous times. But now a new problem arises. She ran horribly with it on! Inconsistent power, bucking, missing real badly. I messed with the timing to no avail. Vacuum did not improve one bit. This is supposedly the correct AFM (#A31-000-050), matched up to ECU# A11-600-000. I put the mismatched one back on, she liked it a lot more. How freaking strange. What in the world is going on?

In both cases, I am in fact lean, as you called it FastWoman.

Oh yes, and on Tuesday my friend will bring a yogurt cup for me to class, so I'll be able to try the yogurt cup test (although it will be with the ripped-ish boots). And as far as I can tell with my timing light, my advance is working. I've gotta be honest with you guys, I'm getting really tired of my EFI.

Yes, you've got the terminology right -- closed vs. open.

The turquois stuff is strange -- definitely not OEM. Is it oily? Perhaps its some sort of contact grease. More likely the turquois color is copper corrosion. Anyway I'd clean it all out. Be certain that all your internal electrical contacts are good (and not corroded) -- especially the fuel pump shutoff switch, which might have been giving you some grief.

It's great that you're running again, sort of. You'll definitely need to address the ripped boot issue. Do you have a new boot on order? The yogurt cup should help you track down any vacuum leaks, so that you'll run richer. If all else fails, we can mess with the coolant temp sensor resistance, but first it's good to check all the simple stuff.

Progress!

Edited September 12, 201113 yr by FastWoman

No, it isn't oily. It's crusty, definitely splashed onto the backside of the cover a one point. Very strange. I'll clean it, probably spray it with some contact cleaner. Ehh, I'm hesitant on ordering the boot by itself. I'm a bit neurotic about saving money on shipping see, and I have a lot of things I want to order. I am neurotically frugal , my parents taught me well. I'm running a bit low on funds right now, but I'm waiting on news from my local Goodyear tire shop, my neighbor is in with the manager there, and he's waiting on some official business to happen before he hires me, then I'm officially a tire man!

Oh yes, news worth mentioning: a HybridZ man told me my lack of a PCV valve could be causing my lean condition, as the intake would be constantly drawing in unmetered air from the crankcase via the vacuum it produces. Less fuel would be injected than required, leading in a lean condition. Makes sense to me. This could also be causing my low vacuum, yes? I'm off to Autozone to pick up a cheapy PCV soon then, hopefully that'll make a difference. Ok off to bed now, very tired. :sleepy: I wouldn't be getting anywhere without my forum peeps, thanks!