258 vacuum line routing & a round of "what is this?"

I'm on hacker patrol under the hood of my newish-to-me 1975 CJ5 4.2l. See my build thread for the ongoing saga of my buildup.

I thought it best to ask in this area about vacuum lines. When I got the Jeep, the PCV line was plumbed into the carburetor fuel bowl vent. I'm chasing down the various missing and mis-routed vacuum lines. Got the evaporator canister buttoned down now.

It looks like vacuum advance is coming directly off of ported vacuum on the Carter YFA 1bbl. Seems like they routed around the CTO (?) switch on the block:


Here's a shot of a short circuit vacuum line routing on two vacuum (I assume) ports on the YFA. Is this bad (looking from passenger side underneath stock air cleaner)?


And lastly, what is this metal tube? I can feel it going down and into underneath either the intake or exhaust manifold. I haven't measured it for vacuum yet:


Thanks for any insight. I've seen the online diagrams here (http://www.jedi.com/obiwan/jeep/misc/vacuumhoses.html), but still can't figure it out.

 

the metal tube is for the automatic choke...its a heater for the spring located in the factory choke housing. id plug the other two if you aren't going for a resto...provided it runs ok...

 

I suggest you buyt the 1975 TSM - it covers your Jeep and all of these systems. There is a is a '74 and a '76 TSM at www.oljeep.com but there are some differences between the years. The '75 electrical is more like the '76, and almost everything else is more like a '74. Emissions stuff changes every year, so you really need the '75 book.

All the Jeep retailers sell this manual - http://www.bjsoffroad.com/prod-670.htm - you can get a modest discount if you buy it from BJ's and are a member of IFSJA or FSJN.

The CTO on the side of the block switches from manifold vacuum to ported vacuum as the engine warms up. This is the "spark CTO." You can bypass it, but if the rest of the emissions systems are connected, the Jeep will have better drivability when cold if it's hooked up.

The circled pipe



is the connection to the choke heater. There is a pocket in the exhaust manifold (open to the air, not exhaust gas) that provides hot air for the thermal choke.

I would guess that the tube in the foreground is intended to route the vacuum from the spark CTO to the distributor, providing some heat protection. Usually these engines have steel tubing with short lengths of rubber hose, to connect the vacuum that goes past the exhaust manifold. Rubber hose would melt and burn in that area.

 

I'm a guess the lefthand pipe in the pic is actually from the EGR system. Do you still have a CTO switch in the forward hole in the block? The rear CTO switch should be for the Vacuum Advance Modulation system

 

Could be. But it would have to be for a vacuum signal. Exhaust gases only go through a pipe on the later manifolds.

TSM says the 49-states 258 CJ has no EGR. But it also says that all '75 258 CJs have no Air Guard (air injection) which I know from personal experience is wrong for CA. And the OP has plugs, as if the Jeep came with Air Guard.

The intake is not machined for EGR, if the Jeep has no EGR. There should also be an EGR CTO in the side of the block, which the OP has not asked about.

 

This stuff is for a 74...may be same?

 

Thanks for the responses.

There is not a CTO in the front of the block (that is, no EGR CTO). It's plugged off as if it's been that way its entire life. Nor is there an EGR on the manifold. It also has a block off plate that seems original to me. Although I live in CA, the story that came with this Jeep is that it only recently entered the state - so I'd surmise it's a 49 state car if I were a betting man.

Back to the questionable foreground tube in the picture - I don't believe it was for the spark CTO. It doesn't match up with the diagrams above and moreover I can feel the other end somehow connected to either the exhaust or possibly the intake manifold. In other words, at the other end of the pipe in question (the end not pictured), there's no way you could connect a vacuum rubber line to it.

Oh and thanks for the link to the manual. I'll put that on my must-buy list.

 

Although I've never seen an "Air Guard" system, I think that's the best guess so far. My intake manifold does indeed have plugs screwed in on each cylinder. Here's some more photos to help solve the mystery:

You can see the top (open) portion of the Tube to Nowhere just above the valve cover on the right sight of a vacuum line that runs to the distributor advance:



...and now the moment I've all been waiting for... actual photographic evidence of where the Tube to Nowhere goes. Thank goodness for iPhones; my nice Canon couldn't focus on this area to save its life. The bottom of the Tube to Nowhere connects to the exhaust manifold:


(yet I still don't know what it is)

 

You can remove the "tube to nowhere" completely. The tube in the bottom of the manifold that it is currently shoved into is to be left open as it's the intake of the "choke stove".
You could leave the tube there as its not doing anything harmful (or useful).

Try to get a further back pic from above to show where those other carb port hoses go.