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V6 Vacuum Leak Finally Discovered ( Pcv )

Discussion in 'Early CJ5 and CJ6 Tech' started by maurywhurt, Feb 10, 2021.

  1. Feb 10, 2021
    maurywhurt

    maurywhurt Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Western North...
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    I've long suspected I had a slight vacuum leak on my '67's Dauntless, but until a few days ago I'd never located it. I thought I'd post this just in case any other Dauntless owners out there may have the same issue, but are unaware of it.

    I'd noticed for awhile that the PCV valve had a slight but noticeable "lean" to it. I'd been thinking this was just the result of the 3/8" vacuum hose pulling on the top connector of the valve a bit, causing it to tilt.

    [​IMG]


    However, after some research I finally figured out that the PCV grommet installed in the valve cover, though it appeared to be the correct one....wasn't. The I.D. of that grommet was about the same as the diameter of the barb on the PCV valve's lower connector, so the grommet couldn't create a sufficiently tight seal. This factor, in combination with the valve's lean due to the pull from the hose, caused a vacuum leak. In hindsight I'm asking myself why I didn't figure this out sooner....

    The old PCV grommet installed by the prior owner was a Dorman 42065. The correct Dorman version of this grommet for the Dauntless is a 42056. The 42065 (marked "65") is on the left below, and the new 42056 (marked "56") is on the right.

    [​IMG]


    The main difference between them is that, according to Dorman's website, the I.D. of the 42065 is 0.566 in., and the I.D. of the 42056 is 0.418 in. - so the 42056 provides a much tighter fit on the PCV valve.

    After changing out the grommet, the engine now runs a good bit more smoothly when using the choke on cold starts (i.e. on fast idle) than it has in the past. For good measure, I also replaced the the PCV valve, and changed out the hose to a new formed one that won’t tug on the top connector of the valve:

    [​IMG]

    Along with the above tweaks, in an effort to increase the airflow through the PCV system, I also cleaned out the air cleaner breather / filter that plugs into the grommet on the driver's side valve cover. It looked pretty gunked up inside, so I soaked it overnight in carburetor cleaning solvent, which did the trick (though I had to repaint it afterwards, as the carb cleaner stripped it down to bare metal).

    In case anyone else needs one, the least expensive source I've found the Dorman 42056 available from is Amazon: Amazon.com: Dorman HELP! 42056 PCV Valve Grommet: Automotive
     
    Last edited: Apr 2, 2021
  2. Feb 10, 2021
    BJHitson60

    BJHitson60 Member

    San Rafael, CA
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    Good to know - thanks!
     
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  3. Feb 11, 2021
    Beach66Bum

    Beach66Bum 1966 Tuxedo Park Mark IV 2024 Sponsor

    Big Island on...
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    Thank you Maury for this great information!! Going to check mine. I do remember when I replaced the PVC it did fit snug, but that was 5+ years ago now.
     
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  4. Feb 11, 2021
    Duff

    Duff Member

    Trump Country
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    I'll be checking mine also. Thanks!
     
  5. Feb 11, 2021
    jeep2003

    jeep2003 Well-Known Member

    Upstate NY
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    I didnt know it had to seal that well. The block isnt going to hold any sort of vacuum
     
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  6. Feb 11, 2021
    givemethewillys

    givemethewillys Been here since sparky ran it. 2022 Sponsor

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    Good catch! Do you have a part # for the pcv hose that you used?
     
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  7. Feb 11, 2021
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Agreed, I think it's the new PCV valve or hose that solved the problem. The block is vented through the other valve cover to the air cleaner to the atmosphere, so it can't hold a vacuum.
     
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  8. Feb 11, 2021
    maurywhurt

    maurywhurt Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    That thought hadn't occurred to me, but you both may very well be correct.

    I wonder if the fact that the PCV valve was at somewhat of a tilt, due in part to the I.D. of the grommet being too large, could have caused the valve not to operate as efficiently?

    My understanding is that PCV valves have a weighted pin which closes when the vacuum is higher, as it is at a normal idle, but opens when the vacuum is lower at higher engine RPMs.

    If this is correct, would the valve work still work the same way if it was out of plumb? I think maybe the PCV valves have a spring in them as well, though, so maybe they don't have to be vertical to work correctly.
     
    Last edited: Feb 20, 2021
  9. Feb 11, 2021
    maurywhurt

    maurywhurt Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    I just found these diagrams showing how PCV valves and systems work on normally aspirated engines. Since the valves have a spring around the weighted pin, it looks like they don't need to be at or near plumb in order to work properly.

    [​IMG]

    [​IMG]
     
    Last edited: Feb 14, 2021
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  10. Feb 11, 2021
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Generally I don't think they need to be vertical since the vacuum is counteracted by a spring.

    They can however, get gunked up and stuck. If it gets stuck at the "Normal Operation" or "Accelerating and High Load" positions there will effectively be a vacuum leak at idle.
     
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  11. Feb 11, 2021
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    ...that said, It's awesome you found a grommet that fits correctly!
     
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  12. Feb 12, 2021
    maurywhurt

    maurywhurt Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    I actually assembled that hose from some parts available on Amazon (and/or eBay) that I'll post links to below.

    The idea for this came from looking through photos I've saved of Dauntless engine bays. The majority of these show a piece of straight hose looped from the PCV valve back behind the air cleaner down to the base of the carb, like mine had previously - but a few had molded PCV hoses.

    The molded type I found photos of were mostly on Jeepster V6's. When I checked with one of the Jeepster parts suppliers, they were familiar with the part, but said no one makes a reproduction of it.

    Here are a couple of examples of original molded Dauntless PCV hoses on Jeepsters:

    [​IMG]

    [​IMG]


    Update 2-25-21: I just found what appears to be a very similar molded PCV hose in a photo of a stock 1971 Renegade - so in addition to Jeepsters, it may have also been used on some V6 CJ's:

    [​IMG]


    Here's an image of a '68 CJ-5 Dauntless with what appears to be the same PCV hose:

    [​IMG]


    This 1970 Ren 1 also has the same PCV hose:

    [​IMG]


    Another example showing a good shot of the original PCV hose - not sure of the model year (thanks, Rubicloak!):

    [​IMG]


    Links to the parts I used to make mine:

    3/8" molded fuel line: https://www.amazon.com/dp/B07C8YTNPF/ref=cm_sw_r_em_apip_buKnUGehEcXdQ

    3/8" elbow: https://www.amazon.com/dp/B000C5I4BK?ref=ppx_pop_mob_ap_share (note: I trimmed off part of the rectangular reinforcement so the clamp would have room to fit)

    3/8" double-barbed hose fitting: Anderson Metals 57014-08 Brass Hose Fitting, Union, 1/2" x 1/2" Barb: Amazon.com: Industrial & Scientific

    I already had the spring clamps, but they're similar to these (I think some were 1/2" and some were 5/8"): 5/8 O.D. Inch Spring Action Hose Clamps Gray 20 Pack - - Amazon.com


    Here's the assembled hose:

    [​IMG]

    [​IMG]
     
    Last edited: Jan 19, 2022
  13. Feb 12, 2021
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Clever to piece it together. That setup really looks great.
     
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  14. Feb 12, 2021
    givemethewillys

    givemethewillys Been here since sparky ran it. 2022 Sponsor

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    X2, great job. Likes much better than the forced curve of the straight hose that's on mine.
     
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  15. Feb 12, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    That "swan shaped" hose is an interesting product. I'll have to remember that.
     
  16. Feb 12, 2021
    maurywhurt

    maurywhurt Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Tim, you may have noticed that in addition to 3/8", it's also made in 1/4", 5/16", and 1/2".
     
  17. Feb 12, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Actually, I did! :coffee:

    I looked for 1/2" because my J20 has a PCV breather that's 1/2" ID ... which I made from some PEX plumbing elbows and straight hose.
     
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  18. Feb 13, 2021
    Bob

    Bob Member

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    That’s great info, Maury! I’m going to use that grommet and molded hose setup. I know my grommet doesn’t provide a snug fit for the PCV valve.
     
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  19. Feb 15, 2021
    71CJ54WD

    71CJ54WD Sponsor

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    I can say for certain a leak around the PCV will cause the vacuum leak you describe. The block does not hold vacuum but there is plenty of restriction when youre pulling up through the passenger side valve cover and the intake for that air is on the driver side valve cover. I had the exact same issue and a new grommet fixed my leak that prevented a stable idle (due to the vacuum leak).
     
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  20. Feb 15, 2021
    maurywhurt

    maurywhurt Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    That was my experience too. The new grommet - possibly in conjunction with the new PCV valve and hose, in my case - fixed the previously very rough idle my engine always had just after a cold start.
     
    Last edited: Feb 23, 2021
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