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

The intake system pulls a vacuum on the crankcase when the PCV system is connected properly. So any leaks in the PCV or through the valve cover gasket or the big hose from the valve cover (actually part of the PCV system) are leaks in to the intake manifold, bypassing the AFM vane, causing a lean condition. All air must pass through the AFM for the EFI system to work correctly, no exceptions.

Are you sure that your PCV is missing? There's not much to it and looking from outside (how did you get your eyeball under there?) it looks like a flat disc sitting in a metal fitting. They do get gummed up (maybe that's the carbon), but can be cleaned with some carb cleaner.

I had the contact switch in my newly rebuilt AFM stop working right after I got it. I think that a small piece of debris got on to the tiny contact switch and kept it open. I never found whatever was holding it open, but after I mucked around with it and put it back together it's worked fine ever since.

Well, my patented yogurt cup test will tell you if you have a leak in the PCV circuit. However, you're not going to get much meaningful info with a humungous leak in the boot. Maybe you can hold your hand firmly over the mouth of the throttle body to seal the air?

A missing PCV valve would certainly introduce a huge vacuum leak (and lean running), but a malfunctioning PCV (but not leaking) would just result in a dirty engine. All of the PCV air is metered and simply makes a circuit through the crank case and valve cover.

Zed Head: Well, I popped off the hose coming from the intake to the block, and I understand the PCV is supposed to be plugged in at the block. What I felt was a plastic-feeling pipe coming off the side of the block, I didn't feel anything like a PCV valve in it. Now, if I was supposed to remove the pipe-fitting from the block to find the PCV, I didn't do that, but it really felt pretty damn stuck. I checked the hose, I pressed around on it, nothing. So I presumed the PO took it off for some reason. :stupid:

FastWoman: They're not huge leaks, just one small rip that I found. I'll hope that the RTV sealed it, and I'll try the test again when I get new boots. And that cigarette smoke test, I'm hoping to try that soon. That should yield some good results, right? :paranoid:

Hey guys, just got a PCV valve from autozone today, but the fitment doesn't make sense. I initially thought I could just stick it in the hose and that would be it, but I see there are threads on the valve, so that can't be right. But there are no threads on the blue plastic fitting sticking out of the block. I really don't know what's going on. How can the valve possibly seal up if it can't thread to the block? If I just stick it in there, the vacuum is still going to leak past the hex pattern on the valve, the fitting is circular. I'm stumped.

And I hope it's ok that I just keep posting in this thread and not make new threads for every question I have. I think that's better, less clutter yeah?

Edited September 15, 201113 yr by ll77

The PCV valve screws into the underside of the intake manifold, about in the middle, and closest to you, as you view the engine from the driver's side. Obviously the hose then clamps to the barb on the PCV valve. The other end of the hose leads forward and downward, connecting to a pipe that comes out of the lower front driver-side of the crank case.

Oh :stupid: I was convinced it was supposed to screw into the block for some reason. Thanks. I might not be missing it after all then. :embarrass:

Yeah definitely not. I can see how it really would be a massive vacuum leak if I were missing the valve. But I see it haha. I'm so embarrassed.

Edited September 15, 201113 yr by ll77

No worries. It's pretty hard to see.

Hello once again,

I have been ill lately, turned out to be a case of acid reflux. It is also finally that time for me to fill college applications again, so it's going to be a busy month.

So last week, I prepared for the rain by putting my cowl back on, throwing the new wipers on, giving her the whole Rain-x treatment. I took off my PCV, it was very schticky. I sprayed it off w/ CRC electrical contact cleaner for fear of there being plastic in there. It worked beautifully. No noticeable difference though. Then it was time for dinner.

I've been turning the big issue over in my head lately, which is that she won't pass smog due to an incredible excess of CO emissions, HC and NOx are very well within limits.

With that being said, I don't understand how I could be running lean, but making such amounts of CO. CO is produced in combustion situations deprived of oxygen. If I am running lean, that means my air>fuel, which should provide plenty O2 for for combustion.

I have a theory that involves my VERY advanced valve timing:

When the piston is at the end of the exhaust stroke, the exhaust valve closes, the intake valve opens and allows spent exhaust into the manifold (?), and the oxygen-poor exhaust gases recirculate into the cylinders at the intake stroke, resulting in a low-oxygen situation in compression and power strokes, resulting in excess CO. This could also cause my low-vacuum situation.

A neighbor suggested I advance my ignition timing to compensate, but ignition timing is irrelevant to valve timing in this regard, because no matter how much I crank up my ignition advance, I will only be further from timing both according to "crank timing," because that is really the central timing event, valve and ignition timing should both be accommodating the piston cycles.

I remember waaay back, I used to think it was because of my exhaust leak, but now knowing that I have no O2 sensor, no.

But I really don't know. Gotta give me credit for trying. Still don't know why it's lean though. I'd appreciate some thoughts, thank you.

You're going to have to get a Californian to help you with that. We don't know what CO is here in Virginia!

I've got bad news again, I've been noticing some hiccups, like as if the engine shuts off for a split second then comes back to life, kind of like how my heart skips a beat when it happens. Then last week it's started doing the "runs like crap for a few minutes on 2nd start-up" thing, then returns back to normal. Both symptoms lead me to think that the AFM is taking a dump on me. Couldn't be happening at a worse time, midterms are this week!

My question is, what kind of problems could running a 78 AFM + ECU on a 76 cause, if any? The only explanation for why the 76 AFM I bought doesn't work with my car, is if the PO swapped the AFM and ECU for a 78 setup, which has the same ECU # of A11-600-000, but different AFM models. So now I'm thinking about getting a 76 ECU, considering they come pretty cheaply sometimes on hybridz. Good idea, you think?

I could be wrong, but momentary lapses in running are most likely due to a bad connection somewhere -- maybe your ignition. It's unfortunate that these intermittent problems are so hard to track down. I fear you're going to have to put up with the hiccups until the car dies and stays dead. Then you might have a chance of diagnosing it.

Until that happens, I'd carry an emergency diagnostic kit with you for testing on the side of the road (or hopefully in a parking lot) somewhere. Carry some starter fluid to spray into the intake. If the engine will fire and then die on a good shot of starter fluid in the intake, then the problem is fuel related. If you can't get it to fire and die, then it's probably ignition related. Alternatively your entire system might be dead. Check for power to the (+) terminal of the ignition coil with a multimeter. Also go through your fuse box to see which circuits have power and which don't. So I guess that's your emergency diagnostic kit -- a multimeter and a can of starter fluid. Good luck!