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Questions About A 72 With A 304

Discussion in 'Intermediate CJ-5 and CJ-6 Tech' started by joltes, Aug 13, 2019.

  1. Aug 13, 2019
    joltes

    joltes Member 2019 Sponsor

    Wheeling, WV
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    I know the basics of what an engine does and how it works, but everything, it seems, has its own supplemental systems that help everything run. Vacuum is one of those systems that I have little knowledge on. That being said, I have a few parts here that I don't know exactly what they do, or if they are crucial to proper operation.
    I believe that this is a coolant temperature override "switch". It is obviously broken. What does it do? Any source for a replacement? I've looked on the net and only found one thing similar to it... It seems to go to a contraption mounted by the coil. Any idea what that does? Picture below with a red line showing the route.
    Next is the limit fill valve, as named in the TSM. It is for the vapor recovery system. Any source for it? Is it just a check valve?
     
    Last edited: Aug 13, 2019
  2. Aug 13, 2019
    Lockman

    Lockman ..... He who dies with the most Tools... Wins ! Sponsor 2019 Sponsor

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    Vacuum is built in the intake manifold by the engine running. Engine MFG's use vacuum to operate switch's and other ported fittings. It's a form of calibration & orchestration for tuning.Hoses dry out , wear out & disenagrate. The good news is that replacing vacuum hose is Cheap ! An engine with vacuum leaks will run poorly & Bum one out........

    1st : Rock Auto
    JEEP 1972 CJ5 5.0L 304cid V8 Electrical-Switch & Relay Ported Vacuum Switch

    2nd : Yes : Rock Auto
    Hoses/Lines & Clamps Vacuum Hose Vacuum Hose Check Valve
     
  3. Aug 13, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    You are quoting the TSM - the TSM describes the function of the CTO/TCS, page 4A-4.
     
  4. Aug 13, 2019
    tomasinator

    tomasinator Member

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    Is that a Ford 2100 carb? I didn't know they put those in jeeps, but I admit I don't know a lot.
     
  5. Aug 13, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    It's a Motorcraft 2100. Not exactly the same as the Ford version, but close.
     
  6. Aug 13, 2019
    joltes

    joltes Member 2019 Sponsor

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    Thanks! It's a lot easier to find things on Rock Auto when you know what they call it.
     
  7. Aug 13, 2019
    joltes

    joltes Member 2019 Sponsor

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    Thank you. I wish the TSM had an index. These kind of things would be easier to find.
     
  8. Aug 13, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    Could you post a better picture of the second item? I'm skeptical that it's a valve like Lockman points to. The TSM describes the limit fill valve, and the drawing suggests it's located at the firewall, not on top of the engine. From the TSM description it seems more like the purge valve in the top of a manifold-vacuum controlled style of vapor canister (charcoal canister). The next few years of Jeep used a similar canister, but purge came from the draft at the inlet of the air cleaner - no manifold vacuum controlled purge, like suggested here for 1972.

    So you don't have anything connected to the vapor canister that looks like the drawing of the limit fill valve? Unfortunately I did not look closely at that part in 1972, so I have no memory of what it should be. The purge valve controlled by manifold vacuum is available separately from the canister in some Chevys - that may be a better substitute for the limit fill valve. I can look through the listings more later.

    Just FYI, somebody has repainted your engine with the later turquoise engine enamel. Lots of the parts have been oversprayed that should not have been, like the fuel tubing and brackets. If you are concerned with accuracy, the engine should be the metallic deep blue-green that we saw in this thread, post 35 Cj5 Is It My Water Pump? - unless it was delivered in California, then the engine would be red (1972 only!)
     
    Last edited: Aug 13, 2019
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  9. Aug 13, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    Looking in the books a little more, the limit fill valve appears to be a Jeep PN 5350854, a one-year only (1972) part that the book calls a "Valve, Fuel Vapor Vent." I'm predicting it will be purest unobtainium, and you must figure out a work-alike, if you need one.

    Unless I wanted to be period correct, I would put together a system from available parts that functions somewhat differently. Holler if you need help with that.
     
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  10. Aug 13, 2019
    joltes

    joltes Member 2019 Sponsor

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    I didn't realize that the third picture didn't post. Here it is.

    That little valve has a line from the vapor canister in the rear and a line to the valve cover. I don't know if it pulls a vacuum from the valve cover somehow, or if the vapors from the canister get pushed in from changes in pressure in the gas tank.
     
  11. Aug 13, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    Yeah, that's definitely the limit fill valve. As I mentioned, NLA. Somebody may have one in a cache of NOS parts somewhere in the nation, but I predict it will be like hen's teeth to find. Looks like the top is broken off and you can see the diaphragm. I suspect there would be a third line going to manifold vacuum that makes the purge signal.

    The TSM shows a charcoal canister. Do you have one under the hood? TSM picture shows no connection to the valve cover, unless it goes through the valve cover to the PCV valve. The canister under the rear quarter is just an expansion tank, AFAIK.
     
    Last edited: Aug 13, 2019
  12. Aug 13, 2019
    joltes

    joltes Member 2019 Sponsor

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    I think the charcoal canister is only on automatics in 72
     
    Last edited: Aug 13, 2019
  13. Aug 13, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    Huh. Yes, the TSM confirms that.

    Not sure how you will duplicate the function of the limit fill valve if you can't replace it. Maybe you can repair the one you have.
     
  14. Aug 14, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    Just to check my thinking, this is how I think the limit fill valve works. It's an orifice with a seal under a spring that allows vapors or air to pass in either direction at a low pressure difference. A few inches of water is a small fraction of a PSI. Normally any vapor pressure from the gasoline would be contained in the expansion tank. If there's a change in pressure due to the temperature, the spring is weak and allows pressure mostly to equalize. There also has to be a way for air to enter the tank, to make up for the volume of fuel removed when driving. Too much vacuum above the tank will stall out the fuel pump. This arrangement seems quite primitive to me, since the only vent is through the crankcase, and there's not much to stop any released vapors from entering the atmosphere.

    This valve has an unusual capability in my experience, and I suspect you won't find a work-alike part.
     
    Last edited: Aug 14, 2019
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  15. Aug 15, 2019
    joltes

    joltes Member 2019 Sponsor

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    I was thinking it was a one way valve that let fuel vapors out of the tank to be combusted, allowing for expansion of the tank gas due to temperature, but only when the engine was running at higher than idle speed, so it wouldn't cause stalling or sputtering.

    I didn't really give any thought to the need for a vacuum release. Isn't that a feature of the gas cap though, to let air in when needed, but otherwise contain vapors from escaping?
     
  16. Aug 15, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    A vented cap passes air or vapor, but I believe your cap is sealed. Caps for systems with vapor recovery are sealed.
     
  17. Aug 15, 2019
    joltes

    joltes Member 2019 Sponsor

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    So, this is all academic here, since the part is not repairable, nor can I find a replacement. However, we can try to figure out what the heck this thing actually did.


    The top still, somehow, has the diaphragm and plastic disc sitting on it, though there is nothing holding it on there. I can't believe it hasn't fallen off or blown away. I am guessing that the bottom had a similar diaphragm on it.

    One connection comes out of the top port in the middle. The other side connection enters into the throat. The bottom port goes out through the side hole that doesn't have a port connection.

    Maybe the diaphragms had different spring strengths holding them closed, allowing one to open under less pressure than the other?
     
  18. Aug 16, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    Since you have good pictures of the part now, you might try to find one using the WTB (want to buy) forums on the various Jeep forums. Assuming you want to put it back like original ...

    No time to go further with this right now. I have a couple of ideas about how you can restore this, depending on what you want from your Jeep.
     
    Last edited: Aug 16, 2019
  19. Aug 16, 2019
    joltes

    joltes Member 2019 Sponsor

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    My overall plan is to get it on the road and then bring it back to as close to original as I can, so workarounds will be inevitable. I’m sure it will run just fine without this part, but I also don’t want to smell gas all the time from it venting to atmosphere. I would be interested in whatever ideas you have to share. I have already replaced my gas tank with a newer year tank, so my vents went from 4 to 3. I capped one of the inputs into my vapor canister to make up for this. I still need to find out how the canister was originally mounted under the rear fender, as the PO had rigged it to a piece of sheet metal that has rusted away.
     
  20. Aug 17, 2019
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    Hi Candace -
    This plumbing is entirely about emissions, and if Jeep designed it right and the rest of your tuning is to spec, you should notice no difference. Do you understand the difference between ported and manifold vacuum? Ported vacuum comes from a port on the carburetor that is blocked and goes to zero at idle. Otherwise, ported vacuum is the same as manifold vacuum. You can run manifold vacuum to the distributor all the time, but emissions at idle will be higher (more advance, hotter combustion, more oxides of nitrogen aka NOx). More advance means more power generally, so Jeep runs manifold vacuum to the distributor when the engine is cold to make stalling less likely, improving "drivability." Once warm, at idle you don't need any power so all that's required is enough advance to keep the engine running, with lower emissions.

    You might notice a difference if you connect ported vacuum to the the distributor all the time, with the engine more sluggish when cold. This is all covered in the TSM, if you read the accompanying text. Note that the '74 TSM is not a reliable reference for emissions systems, because these systems were evolving rapidly due to changing legislative requirements and technology in this era, and you need to refer to the TSM for your year. In '72 the CTO is connected in parallel with the TCS, so your plumbing will be different.

    Also, it's fine - strongly preferred - to start another thread with a question not directly related to the original topic. It's considered impolite to "hijack" a thread like this for your question. If you hijack, the mods will likely intervene and split off your post into a separate thread. Also, if you pick a descriptive title for your new thread, in the future owners searching for info on this question are more likely to find the answer. The forum is supposed to be a technical reference in this way. No problem for me - I'm just sittin' here after breakfast - just FYI.
     

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