I have a 1989 XJS Convertible V12. In the engine bay on drivers side close to firewall there is a rubber tube about three feet long, On the end of it is a nylon cylinder with some type of filter in it, It goes nowhere. It has a fitting in the end which looks like it would attach to another rubber hose, looked all around and could not find anything it could attach it to, Any ideas?

 

Vent line for distributor cap. Nothing attaches at filter end. Other end attaches to distributor cap.

 

Thank you so much for clearing that up for me, Makes sense now,

 

there should be another tube from the distributor to the intake manifold,
air is drawn through the distributor through the filter on the end of the pipe you have, this is to prevent the build up of Ozone in the distributor, this is created by the sparking effect of the system , effectively mini lightening , ozone is corrosive and effects the efficiency of the spark, hence the need for ventilation, nothing to do with oil or fuel fumes as some believe.....

BB

 

Thank you, good to know

 

There should be two tubes on the dizzy...

If that is a line coming from the distributor (more on the LH back of dizzy) and you are finding it's end on the LH side, the LH line should connect to a little spigot on the back side of the TUBE/HOSE (if it's OE) running between the back of the LH air filter inlet housing/breather to the AAV... The suction/vac provided draws air (small amounts) and moisture thru and out of the distributor.

I believe,,, the end that has the filter should be in place on the ENTRY tube thru the distributor on the RH side of the engine bay or at least entering the distributor on the back RH side. Where the hose originates from I guess is only dependant on where one places it.

It could be that the PO used a vac spigot off the intake manifold (somewhere) to draw that air thru the dizzy and reversed things for some reason BUT, in my mind, routing it directly into an intake that way would allow too much extra air into the intake, aka a vac leak. The OE design on the breather case to AAV doesn't allow a vac leak extra air situation.

 

Thought I'd post some pics and thoughts on this topic as I'm building this out, also...

I replaced the lawn mower filter with a breather and am either going to route straight to the intake or through the oil catch can I'm adding, not sure yet. Doesn't matter which fitting used on the distributor as long as one side sucks and one side breathes, preferably with some sort of filter on the air being sucked in. It's really that simple.

As to connecting directly to the intake... So, I've gotten rid of the intake boxes and trumpets and AAV, but the sucking line is through the AAV hose connected to the back of the B-bank air intake box. It's not impacted at all by the AAV function, it's just using that hose as the part that provides the sucking to pull air from the distributor. That AAV tube is connected to the air box and the air gets sucked through the throttle body. I don't think it gets too much "filtering" as it's coming in through the back of the box and not through the trumpets. Not sure the amount of vacuum it's seeing through that connection, but it's probably not too different than a direct connection to one of the intake fittings.

Now some pics...


Breather - air pulling into distributor

Yellow hose attached to intake to pull air form distributor

Fittings covered in blue tape - nothing special, just open holes into the distributor housing...

 

Damn, Man... I like your style!!!
Nice looking engine bay.
The colors are dynamite!

 

If those hoses are connecting to the spigots on the center top of the intakes, where the big ol goofy Y pipe used to be,,, that's a LOT of air going thru the distributor, no?

When I have that intake spigots that draw thru the Y pipe open,,, used to go to the PVC valve connected to the trumpet and the engine breather in a 3 way spot on the LH side,,, a lot of air is moving thru them... A good strong vac. I have a silicone hose that goes from the engine breather cap/pipe to the Y pipe to create a negative pressure in the engine and the amount of vac COLLAPSES the hose at idle. It opens slowly as the throttle is opened... Anyways,

How is your idle with this configuration? Is it effected and did you have to do something to regulate the vac pressure?

 

The main problem with routing the dizzy vent tube direct to the intake, or even via a catch can, is that it will be subject to very strong suction. This, in turn, means that at low revs particuarly, and tickover the moreso, a huge vac is being applied to the dizzy internals.
This can and does often mean that oil is sucked up into the dizzy, thus doing it and the ignition spark pathway no good at all. Now if the entry tube to the dizzy vac is unrestricted, all may be well, but if not, definite chance of a problem.
The OEM tube goes to the AAV (ie tickover air) inlet, and thus is restricted from full vac, as in this photo:

The AAV vent intake is the small protrusion from the AAV inlet tube pointing upwards

This special tube is NLA; but you can use a normal 90 degree hose and install a spigot that is specially made for such things:

 

This is all in the "design" phase, so haven't run the car with this or any of my other mods. I haven't run the car since March when I started this big maintenance project. Long story short - car ran great, but has/had a hot start issue, so I started the project initially testing heat shielding on the fuel rail and lines to potentially prevent vapor lock. That didn't seem to help, so the big overhaul began with new fuel hoses, removed A-FPR, new B-FPR, and that kinda snowballed into a whole bunch of fun stuff like removing all the emissions stuff that I could (live in TX and offset with a Prius), AAV, air intake cleanup, sump tank refurb/filter removal, fuel cutoff, pre-sumo filtering, and the list goes on...

In any case, this is one of the last things to figure out how to best do. The post shows my first thought, easiest install, and probably the coolest looking option, but also probably the least functional - way too much suction I'm installing an oil can right in the little space above the coolant expansion tank which is a perfect fit after being vacated by all the hoses going to the canister. So that was my next thought, but am not sure how much vacuum is going to be produced until I get things running - there are two options here, pre- and post- catch can which might have different vacuums.

Ideally, as mentioned, I'll want a constant vacuum source that is not too strong, just enough to pull all the electrified air outta the distributor (I don't anticipate any oil or other fluid contaminants into the distributor cap as I've hopefully sealed it nicely and the breather filter does its job - disaster could happen, but then I'd have bigger problems that this).

 

Pirk
Concerning hot starting: assuming all the system is as new, rotor, cap, HT leads, amplifiers well heat-sinked/in a cold place, etc etc and that cold starting is bang on:
I read somewhere on here, and I have been thinking about what I read, that during a hot start a couple of goes on the pump, without trying to start, should clear any vapour out of the fuel rail. BUT, the post went on to say, vapour may still be in the tubes leading down to the injectors, as it might not be purged even though the fuel rail is full of fuel.
Now this to an extent chimes with my experience; I do the two goes on the pump before a hot start, then as I turn the starter I floor the throttle, and after a turn or two the engine roars into life. If I do not floor the starter it takes much longer.
Therefore, when I redo my injector tubes at some point, I am going to ensure the flexibles are as short as possible, ie the rail and injector ferrules are close without actually touching (say 1/4 inch apart) thus reducing the volume of any vapour in the tubes.
I chatted with the WOZ, Grant, about this and he said that he had done so and had eliminated hot start churning.

 

I have lots of info and pics and stuff on my hot start experience that evolved into fuel rail and injector cleaning, injector wiring connector replacement, and on, buy didn't want to totally hijack this thread on distributor vacuum hose identification, purpose, etc.

If interested I can start another thread on this or can just continue here if that's the protocol.

 

Cool stuff!! I dont own one that has such s system but I agree direct vacuum to the distributor will come back to haunt you. It would have to be metered in some way either by some kind of restriction or valve or something. Youd basically gave a vacuum leak with just a small filter on the end.