1985 720 z24 exhaust emission tubes

[620Bob]

I have a 1985 Nissan 720 that recently blew a head gasket.  I'm replacing the exhaust manifold, but the two metal pipes that connect the front side of the manifold with the air cleaner are damaged and need to be replaced.  The end of each tube threads into the front side of the exhaust manifold at what may be a 24mm by 1.5mm flare fitting and the other end is clamped into a short rubber pipe near the intake horn on the air cleaner.  It's the flare fitting that has extensive damage to the threads.  I'm having trouble finding the part in useable condition in wrecking yards, and the dealer hasn't been particularly helpful.  Does anyone on Ratsun know the part number, know of a web site that carries it, or have the tubes in reasonable (i.e., useable) condition?  The part number would be great.  Thanks for your help.

 

[Draker]

I'm sure someone in Oregon might have these laying in a parts pile... if they haven't already been tossed in the trash. 

[erichwaslike]

can you take a pic of what you are looking for, i have a 84 im parting and an extra manifold for a z24 also that may have it.....

[xsdg]

OP: the magic search terms you're looking for are "air injection tube" or "air injection pipe".  That said, my understanding was that 1984 was the last model year that used the air injection pipes to the exhaust side.  My 03/1985 720 (CA) uses an AB (Anti-Backfire) valve that lets air into the _intake_ side under high vacuum.

 

This may or may not actually fit your truck, but it should at least get you going down the right path:

http://www.rockauto.com/catalog/raframecatalog.php?carcode=1210385&parttype=4904

[datzenmike]

Can't help much but you could cut them down to 8" or so of the exhaust manifold and use neoprene hose with clamps up to the reed valves on the air filter. Air travels towards the exhaust so they shouldn't get hot. The system uses a one way reed valve to allow exhaust vacuum pulses to draw in air for the cat to work on. .

[Edward Stills]

What purpose do "air injection tube" serve?  Can they be removed altogether?  I do not have an egr valve if that matters at all. 

[Thomas Perkins]

Why did you remove the egr valve.https://knowhow.napaonline.com/what-does-an-egr-valve-do/

 

Edited June 28, 2022 by Thomas Perkins

[Edward Stills]

Hey Thomas!  I hope you are doing well.  It was removed when I purchased the truck.  They also brazed the ports both on the intake and exhaust manifolds.  So no going back without much effort.  So with the EGR valve gone . . . I'm just wondering if I need the air injection tubes.

 

[Stinky]

If you remove em....your truck won't pass smog.

 

Make some outa conduit?

[datzenmike]

The exhaust gasses are rather poor in oxygen due to combustion. For the catalytic converter to burn any left over hydrocarbons mor air needs to be added.

 

The AIS (air injection system) uses the small negative pulse following every positive exhaust pulse to pull a small amount of air from the air cleaner. At the air cleaner are one way reed valves that only open for the vacuum pulses. So the injection tubes convey filtered air in a series of small gulps. The air and the oxygen allow the converter to 'burn' the emissions in the exhaust.

 

This system has absolutely no effect on running. Uses no energy other than that of the exhaust pulses to work. Simple and effective.

 

 

 

[datzenmike]

4 minutes ago, Stinky said:

If you remove em....your truck won't pass smog.

 

Make some outa conduit?

 

The EGR is already been deleted so there is no 'passing emissions'.

[Edward Stills]

Thanks so much for the replies!!  So I live in NC so there is only an "safety inspection" performed each year . . . no emissions inspection.  And this is a good thing for me . ..  I forgot to add to my post . . . the catalytic convertor is gone as well. 

 

So with that being said . . . does it make sense to keep the air injection system intact?  I'm thinking about putting a weber carb on this truck as well . . .. no reed valves in a weber air breather.  🙂

[datzenmike]

No sense at all. Best to make a new bottom for the air cleaner that fits over the Weber. The 720 air cleaner is larger and cheaper than the the Weber and you get to keep the ATC (auto temp control) and the valve cover vent hose functionality. This totally benign system mixes cool/cold ambient air from in front of the radiator with air warmed by the hot exhaust manifold are regulated to about 100F. The engine runs more predictably when it thinks it's summer out all year. By design, at full throttle the ATC deactivates and runs on cooler air from in front of the radiator for max performance. There is no down side to having the ATC functional. 

[Thomas Perkins]

If you want it to run super,Do it like I did...I also had my cat deleted.

 

[Edward Stills]

Nice!  Looks nice and clean. Is there any power/performance/mpg gains with the Weber that you have notice Thomas?

[powderfinger]

Since you live in NC you will not have to inspect this truck at all. Not even the simple safety inspection. Vehicles older than 35 years old require no inspection. 

[Thomas Perkins]

On 6/30/2022 at 12:04 AM, Edward Stills said:

Nice!  Looks nice and clean. Is there any power/performance/mpg gains with the Weber that you have notice Thomas?

Yes,it runs faster,Starts better,Idles perfect.Top end is better.MPG is about the same.The original carbs were a very poor design.And don't have to buy paper air filters any more,Weber filters can be cleaned over and over.I took my 720 to 3 different carburetor rebuild shops,and all charged 200 bucks,and got it back the same ways as when I took it.So I took it to the Nissan Dealer here.All of them people working on them had 30 years experience working on them and told me that they could not rebuild it cause they are a very poor design and told me to get a Weber.I spent a fortune on trying to get the old carburetor right,also replaced all the valves that went to it,they were available from the Nissan dealer back then.This was before the internet was around.So I put a Weber on it and it has been a God blessing.I just recently put a new EGR valve on it.I put a new pioneer throttle cable on when I put the Weber on it,the end piece of the old cable tore up.Auto Zone has the best price for them.I have a new spare one.I use a idle cut off solenoid to make it idle perfect,and keeps it from dieseling.I would bet my 720 against any other 720 that mine runs better and faster.Also I use NGK Iridum spark plugs,they are better than the copper NGK spark plugs.I have lifetime warranty coils from Auto Zone,so every year I take them off and take them back for free new ones,plus my rotor and distributor cap is from Auto Zone,I take them back every year and get free one's too.Water pump,Radiator is from Auto Zone too,so when one goes bad,I take both back and get free ones,Starter and alternator are from there too,never have to buy them ever.Also my oil pressure sending unit is from Oreilly's,have a lifetime warranty,so I never buy that either.Yes,get rid of that carburetor or you will be fighting it forever,also get rid of the cat.Keep your vacuum lines like I have it and you will think your engine is new.When putting a new valve cover gasket on it,torq it by the book to keep from leaking and put silicone in the screw holes and half moon end pieces.

 

Edited July 4, 2022 by Thomas Perkins

[bigleagueteague]

So, I have my eyes on a rebuilt hitachi to hook up to try and get my ‘84 to pass smog here in Boise. Crossing fingers emissions testing is dead here in 6 months, but it’s not certain and I am also tired of shitty Weber winter performance (maybe the thing isn’t tuned right, but I go from 17 to 12 mpg when it gets cold; I know the original filter housing would help).

 

Anyway. I’m rebuilding the emissions system from scratch. I picked up an exhaust manifold with intact egr tube, but it doesn’t have air injection tubes (Cali manifold?). Is there any way I’ll pass without the air injection tubes, or are they absolutely critical to the emission system’s performance?

[datzenmike]

 You mean the tube from the air filter to the exhaust manifold. All '81 and up had them, I think 4x4s used two and it's called the AIS. (air injection system) . Each exhaust pulse is followed by a small vacuum wave. The air filter end has a one way reed valve that only allow the vacuum pulse to pass, drawing filtered air into the exhaust. This air is used by the catalytic converter to burn off much of the emissions. If you have a working catalytic converter you may as well take advantage of this 'free air injection'.

[bigleagueteague]

Yes I’m talking about the two tubes for the air injection system.

 

The manifold I picked up has no ports for those tubes, only the egr tube. It also has an o2 sensor. I’m pretty sure the truck was an ‘84 (it had a pre-‘85 bed), but maybe it had a z24i swapped into it at some point?

 

Anyway, I understand not having the AIS in place won’t affect carb performance, but it will affect cat performance. I’m just wondering whether the lack of AIS will lead to an emissions fail.