So, while replacing the master brake cylinder in my 80 720, I found a handful of vacuum hoses that need to be replaced instead of removed and plugged. At least, that is what I THINK I found. I was thinking of replacing all of the hoses, as I ahve seen that mentioned a number of times in my reading around here, but doing that, and leaving these bare seems silly to me.

So, without further ado, here are some pics of the culprits:



This one shows three of the missing connections. One on the vacuum dealy-o (what is it?) next to the distributer. The second is the bent metal tube just below with a rubber stopper on it. The third is the black hose comming off of the same vacuum dealy-o. There is a better pic of it next.



This is the top of that black hose comming off my mystery vacuum device.



This is a closer pic of the tube with the rubber stopper.



This is another oddball. It seems to want a hose to connect with the bottom of the air breather, but, it is obviously missing, and I haven't found any pics anywhere yet, to tell me where ti is supposed to go.

There is also a hose over on the right side of the engine compartment (as you are looking into it) that is plugged with, of all things, a golf tee. I am thinking this might also belong with all those other loose ends.

Does anyone have pics of their correctly hooked up hoses, or a place to start looking in the Haynes manual?

Also, are all of the hoses supposed to be relatively the same size? Many of mine look very hodge podge and odd. I think this task is long over due.

Any help?

Thanks in advance, and yes, I have searched the tech forums. To no avail.....if you know of a thread, please send me to it.
Modified by Supererogator at 9:36 PM 3/1/2009

Can't help with the hoses but I can tell you that the device you mention is a vacuum delay valve. It's an emission system device that delays the vacuum signal to the distributor for roughly 2 seconds which supposedly has some effect on emission readings. Those are on both my Z and my 810 and they've both passed the smog test with and without them. I can't really tell if the cars run any different performance wise with or without them.

the top pic

the round gold thingy on the left attaches to the round gold thingy on right... just one hose from open end to the open end on the other

More smog stuff. Round gold thingy on left = B.P.T (backpressure transducer) valve, round gold thingy on right = E.G.R. (exhaust gas recirculation) control valve. Exhaust manifold pressure through the metal tube that joins them operates the BPT valve which regulates the vacuum to and the opening of the EGR valve. The less exhaust manifold pressure, the more the BPT valve opens and the more the EGR valve opens. The more exhaust manifold pressure, the less the BPT valve opens and the less the EGR valve opens. Carbon can block the metal tube that joins them which causes the BPT to operate improperly, if at all, which causes the EGR valve to operate uncontrollably.

Sounds as if this symptom may be why the devices are not connected to begin with. Is that kinda what you see and know?

Thanks for the help.

Supererogator wrote:Sounds as if this symptom may be why the devices are not connected to begin with. Is that kinda what you see and know?

Thanks for the help.

What symptom? That the EGR system isn't working? You'd have to hook it all up to find out or if you have a vacuum gun you could check the operation of the EGR and BPT and vacuum delay valves and well as the distributor advance. If they all work, the system will work. My experience is with 280Z/810 emission systems but they have essentially the same components as a 720.

IMH wrote:What symptom?

The plugging of the vacuum tube. Sorry, I may have not phrased correctly.

Basically, it sounds as if these components are not a necessary part of the running system. Maybe, I would be better off just surpassing them as they are , or even removing them?

Back to the hoses. Are they all (obvious exceptions) supposed to be roughly the same size? I kinda want to go to the store and buy a bunch of hose, do the system by taking one piece of, replacing it, and moving to the next. I do not want to have to go back to the store. What extras should I buy? Do I really need two or three sizes of vacuum hose?

I am impressed with the knowledge that has come so far. Nice show. Thanks.

you will need more than one size... but around 90% of them are the same

PEZi303 wrote: 90% of them are the same

Not in my truck, but that is one of the things I am looking to fix. Thanks for the advice. Next weekend is the oil pan gasket, then the vacuum hoses me thinks..... OH, and timing...not right that stuff. Any hints y'all? Or is it pretty straight forward. Attach light and mark spot with chalk, then run motor and adjust distributer. One manual I have says something about plugging a vacuum hose for this adjustment. Do I worry about that?

You'll need to plug the hose so the vacuum advance doesn't work while you're setting the timing otherwise you'd get a false reading or, more accurately, an advanced reading which wouldn't be indicative of the so-called static timing which is what you're trying to set. On the subject of the emission control system, there are many other components. I don't pretend to know the setup on a 720 as I've never owned one but Nissan put a laundry list of stuff into those systems on vehicles that have them. You should read up on the system in the factory service manual to see how it functions and what effect eliminating some or all of the components would have on overall driveability.

there is a high heat hose that goes from the pipe to the bottom of the "bpt" valve, but the rest you could use regular vacumm hose