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

[Jennys280Z]

Happy New Year Sarah! xx

I just measured across the air temp sensor itself by putting the leads on the white nub. :stupid: I didn't see any black wires coming out the back...errr what has to be under the front cover somewhere? I'll look again and see what I am missing.

Here is a photo of that notched tooth that I'm referring to. Notice there is a bowl shaped cut into the space between the teeth which is a sharp edged angle on every other tooth. The tooth in the pink circle I drew, sitting right at 12 o'clock high has a round bite cut out of it. I tried to angle the camera so the light was reflecting off of this round surface so you can see it easier. Sorry for the blurriness otherwise.

[cozye]

notched tooth looks like someone marked it for reference. I used a gold sharpie on mine to mark a reference point.

As far as the fuel pressure goes, I'd say you are right in spec. I know that Sarah mentions that 38 might a little high, but that's what mine gets with the vacuum line off, and I've got two FPR's I've tried. I'd say your fuel pressure is good and you can move on. It does look like you might have a little fuel pressure leaking down on the rail after turned off, might cause a hot start issue later, but I wouldn't worry about this now as it's not your immediate issue.

[FastWoman]

I think the "bite" might be where the screw was tightened down on it at one time. It's sort of hard to tell.

I forgot to mention, BTW, that the only consequence of the pressure leak-down is hard starting. If you're able to start your engine easily enough, then there's no problem.

If you do have a starting problem, you can do like I did and install a switch to run your fuel pump momentarily before starting. That will pre-pressurize your fuel rail, and your engine will fire right up the second you turn the key.

Jenny, now that you have the AFM off of your car, have you tried the yogurt cup test yet?

Also, have a very good look at your rubber boots. If they're cracked (even if the cracks don't run all the way through), you might consider buying replacement boots for approx $100 for the pair (MSA, I think).

Edited January 2, 2011 by FastWoman

[Jennys280Z]

notched tooth looks like someone marked it for reference. I used a gold sharpie on mine to mark a reference point.

As far as the fuel pressure goes, I'd say you are right in spec. I know that Sarah mentions that 38 might a little high, but that's what mine gets with the vacuum line off, and I've got two FPR's I've tried. I'd say your fuel pressure is good and you can move on. It does look like you might have a little fuel pressure leaking down on the rail after turned off, might cause a hot start issue later, but I wouldn't worry about this now as it's not your immediate issue.

The exact same notch is on two AFMs, so this is a factory marking, not by a person's.

While it's possible that the '77-78 AFMs don't have this notch, I would look for it closely the next time you have your front cover open. Use a flashlight and look carefully. With the AFM in the photo above the notch is at top center 12'oclock with a pristine glue blob on the locking wheel. The exact same bowl shaped marker was 2 teeth CW from this position. I took additional photos of the notch on the AFM I took off my car both before and after I adjusted it tonight. It was about 2 teeth lean, now it's going back on my car about 1 tooth rich. Resistance measures between pins 6-8 and 8-9 increased (from 199 to 206, 73 to 80 respectively) after adjusting the wheel, though I'm not sure if adjusting the wheel is the cause of these increases.

My car always fires right up in less than a second, hot or cold, so there's no problem with getting the fuel to the cylinders while cranking at least.

[Jennys280Z]

I think the "bite" might be where the screw was tightened down on it at one time. It's sort of hard to tell.

I forgot to mention, BTW, that the only consequence of the pressure leak-down is hard starting. If you're able to start your engine easily enough, then there's no problem.

If you do have a starting problem, you can do like I did and install a switch to run your fuel pump momentarily before starting. That will pre-pressurize your fuel rail, and your engine will fire right up the second you turn the key.

Jenny, now that you have the AFM off of your car, have you tried the yogurt cup test yet?

Also, have a very good look at your rubber boots. If they're cracked (even if the cracks don't run all the way through), you might consider buying replacement boots for approx $100 for the pair (MSA, I think).

I'll post some pictures of my original AFM I took off to show you the notch when it was a few teeth to the right and now one left of top center. It's a circular notch molded onto the plastic from the factory. No person could make a notch this clean, smooth, circular (perfect) with a hand tool. Let alone do it twice on two independently owned meters.

Also, my earlier suspicions were correct. My AFM was tampered with. The locking nut loosened easily and wasn't held in place by the glue.

I'll take a good look at the rubber boots tomorrow especially the one going to the throttle body which I'll remove and inspect thoroughly, and read up on your yogurt cup test before reinstalling the AFM. I hadn't reinstalled it yet because I was deciding whether to install the AFM I bought (not as pristine looking, didn't clean up nearly as nice as mine, but also unmolested potentiometer) or the one I already had on the car (a lot prettier but molested). Since I adjusted te wheel back to original settings, or close enough, I've decided to install the same one back on.

Nope, starting the motor is definitely not a problem. Fires up without hesitation every time.

And I'm just about certain at this point that I don't have any vacuum leaks at least at all the places near the top where places that can leak vacuum exist. I had a leak at the air regulator after installing all new vac lines and it was so obvious because I could hear it whistling. A bit of sniffing with the carb cleaner and I found the leak immediately.

I think that the low vacuum is just telling me I'm not running efficiently. I've gone from 13in to a smooth 15in with the work I've done so far and no small part thanks to you guys! Tom Monroe (author of "How to Rebuild Your Nissan/Datsun L Engine") said to expect between 16-18 inHg when these cars are running right. He might have also been presuming a brand new engine on saying this, or a brand new rebuild at that, he wasn't clear about that though. So if you're at 17 now with your car, I'd be satisfied with that!

I suspect I'm going to see 16in on my next startup just from the thorough cleaning (and adjusting, testing) of my AFM connectors and innards, along with my new air filter (I thought replacing that was going to be a cinch - NOT! )

Old brake booster is off yaay! Nissan used enough rubber cement gluing the bloody thing to the firewall. It was no match for the mass quantities of WD40 I threw at it, however.

My motor has 140,000 gentle miles on it. 60,000 of which were from yours truly. The first 80,000 were the original owner who was a mild-mannered teacher at a private school.

From here, I still need to adjust my valves, and replace my distributor (cap and rotor too, why not).

The first picture the rounded notch is two teeth lean, the 2nd picture it's 1 tooth rich. Air filter, old and new. Yuck, change your air filter guys! xxx

Edited January 3, 2011 by Jennys280Z

[Jennys280Z]

Edited January 3, 2011 by Jennys280Z

[Zed Head]

That thing I tried to draw an arrow to is a rubber plug. Underneath it is the idle air adjustment screw. You'll probably need a small screwdriver or an awl to pry the plug out. It is about 1/2" tall.

I'm just pointing it out. I don't know if you'll want to mess with it or not. If you're trying to get things back to stock performance, you probably want to leave it alone for now.

Edited January 3, 2011 by Zed Head

[Jennys280Z]

That thing I tried to draw an arrow to is a rubber plug. Underneath it is the idle air adjustment screw. You'll probably need a small screwdriver or an awl to pry the plug out. It is about 1/2" tall.

I'm just pointing it out. I don't know if you'll want to mess with it or not. If you're trying to get things back to stock performance, you probably want to leave it alone for now.

Looks like a screw in there alright...well whaddya know?

Now on inspection I see a square shaped hole in the floor of the AFM body opposite the air temp sensor, and a thin rectangular hole coming out the back...can't believe I missed noticing these before. Time to get the carb cleaner out again.

[cozye]

Interesting about the notch. I'll have to take a closer look on mine.

The orange RTV sealing your cover is definitely not stock. The cover has been off. Nissan used clear silicon to seal the cover.

Also, I wouldn't put carb cleaner in the idle mixture screw area. It's got a rubber seal on the idle screw that is used like a lock nut to keep it from moving. the rubber is hard and probably brittle with age. I would think carb cleaner will just weaken the rubber. The idle air screw is just a big valve that allows air through that sqaure passage to bypass the flap, it's a fine tune on idle air mixture. Carb cleaner wont do any good in this area. No moving parts and the hole is big enough that it won't be clogged I wouldn't think.

[FastWoman]

Yeah, I agree with Eric.

If your motor fires up easily, then forget the fuel pressure leakdown when it's sitting. It's not a problem.

If I were you, I wouldn't mess with the screw underneath the plug. It didn't do anything particularly obvious on my engine. It's probably better to keep it however it came from the factory.

You might still have a vacuum leak. You're forgetting about the junction of the intake manifold and the cylinder head. Your intake gasket could be leaking. Mine was. Moreover I couldn't easily find the leaks because they were on the underside of the intake manifold. (My '78 manifold has heat shield webbing between the intake ports. The yogurt cup test is pretty quick and easy, and it rules out any question as to whether you have a vacuum leak. If you do it, you will probably be the second person in recorded history to do so!

[Jennys280Z]

hi Sarah, well a couple times already I've shot carb cleaner all over the top of the intake manifold gasket. The bottom side of that gasket is a different story. Learning that you were leaking vacuum down there too has me concerned now.

I did the Yogurt cup test but remember I don't have an EGR. So my own version of it at least. I pressurized the manifold with my breath, then plugged the line with my thumb. 15 seconds later I could release my thumb from the end of the line and still hear the air blowing out of the line. 25-30 seconds later I could not hear the air escaping. I was impressed by this that everything is okay, and this is just valves and rings (and a slight leak where I was accessing the manifold's vac (at the brake booster to intake pipe).

I really need to do a compression test which is coming soon, unless I'm lucky enough to have my car running really good and am happy enough that I don't hurry in doing it. Not sure if I'll do this before or after adjusting my valves. Maybe it'd be good to have that as a reference point so I don't go too far out of my way bandaiding a mechanically-troubled engine.

Yes my '76 intake has that heat shield webbing also. GRRRR

No progress reports on my car at this time because Parts Geek are being geeks about giving me an RMA number to return my core, but more time-important than that is whether or not they will void my warranty if I paint/prime my brake booster. It seems to be covered with a dark silver protective coating already so maybe I can just install it as-is. It'd be installed already if I knew what to do. But they don't answer their phones. I am going to send an email tonight. They don't answer their phones.

Sarah you were right... At this point I'm going to get my distributor at Autozone. The extra $15-20 it costs to have the convenience of a place that's open 24 hours a day and with helpful people behind a desk to return my core to, answer my questions, and honor their warranty - looks worth it.

xox

Edited January 5, 2011 by Jennys280Z

[cozye]

another way to test for intake leaks is to use a propane torch. Put a 2 foot rubber hose on the end of it. Then turn it on, but don't light it. The hose will allow you to stuff it in hard to reach places, like under your intake and above the exhaust manifold. Propane actually works better than carb spray in my opinion. Pop a small vacuum line off and hold the propane over it, you should easily hear the motor rev a little. You can also hold the propane nozzle anywhere near the air intake for a test too, and it will pick the idle up. If for some reason you have to hold the propane torch upside down, just remember that the cold liquid propane will start to clog the nozzle after a few seconds and stop your gas flow.