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pcv port and breather port have vacuum on them

Discussion in 'Engine & Performance' started by Handy Andy, Jun 5, 2020.

  1. Handy Andy

    Handy Andy Full Access Member

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    Ok guys, this one has me looking for some answers and ideas. To start off, I'll just say the motor is a carbed 350, dart heads, edelbrock intake manifold and new edelbrock 1906 carb. Nothing real crazy, just something thats fun to drive and it gets used for work around the property as well. We rebuilt it after the 400 that I built for the truck went kaput... I went fairly cheap on the rebuild. The cylinders were fine, so I decided to pass on machine work and just hit them with a berry bar as I wasn't about to bury a bunch of extra money into another motor. I was looking to just get the truck driving again.

    I've been having an INSANE amount of oil fouling on the plugs. Mainly the 1,2,3,4 plugs with 3 and 4 being fricken horrendous... we are talking have to take the plugs out and clean/replace them every hundred miles or so because the cylinder won't fire. I think most of this is because the SUMMIT tall valve covers have a poorly designed baffle in them and with a high volume oil pump in the motor they are actually allowing oil to be sprayed up on the pcv valve and be sucked back into the fuel system. when I pull the pcv valve, it is functioning properly, but the bottom of it is covered in oil, as is the bottom of the breather filter on the passengers side of the motor.

    So, today I decide to go out and do a simple test to see if maybe I have an issue with some piston rings or something allowing a lot of blow by thinking maybe there's something really wrong which is causing a high volume of air through the pcv valve carrying oil out... I went out, pulled the breather filter from the passengers side valve cover, plugged it with a rag, and then pulled the pcv valve out of the drivers side cover. I then held a paper towel over the grommet for the pcv valve and low and behold there is vacuum... and I mean a fair amount of vacuum... immediately my mind goes to a bad intake manifold gasket, or a broken intake manifold all together... I'm going to go out and double check all the intake manifold bolts to ensure they are all tight before I get to tearing things apart.

    My question is, other than a leaking intake manifold gasket, what else could I look for that would cause vacuum in the crank case?

    I've done some looking on my pcv valve issue. Moroso makes a grommet that is enclosed with a slit in the bottm. I'm going to order one of them and give it a try. If that doesn't seem to fix things, I may have to resort to building or buying an oil catch can. I guess we will see. I read that there was at one time some motors using a bit of a riser for the pcv valve to get it up and away from the rockers so as to eliminate the chances of pulling oil through the PCV Valve. Anyone ever seen anything like this?
     
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  2. Rusty Nail

    Rusty Nail Whatever!

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    Yes.

    Not THAT bad, but traced a similar issue to Edelbrock Elite series p.o.s. valve covers.
    AND I too, ended up permanently using an "elevated" PCV valve in that motor. Custom grommet.

    I'll barely even handle baffle-less valve covers long enough to throw them away.

    Buuuuuuttttt....... what spark plugs are you using?

    1,2,3, AND 4?
    Aluminum heads?
     
  3. Handy Andy

    Handy Andy Full Access Member

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    Yup aluminum heads. The front 2 cylinders on each side seem to foul up the fastest, but today I changed all the plugs and they were all very bad. I'd say the front 4 foul 2x as fast as the back 4. I've unhooked the pcv hose from the carb and blocked the vac port on the carb. Gonna drive it like this for a bit to see if it stops fouling plugs. When I have some time I'll pull the intake off and inspect for cracks and replace the gaskets just to be sure
     
    Last edited: Jun 5, 2020
  4. Rusty Nail

    Rusty Nail Whatever!

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    The valve cover in the passenger side pulls vacuum..
    From the breather hole.
    Im at incorrect intake gasket I guess..how the hell could that happen?
     
  5. Bextreme04

    Bextreme04 Full Access Member

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    The valve cover on the passenger side only pulls vacuum if you have the PCV connected on the drivers side and it is at idle. Because the intake is pulling vacuum through the PCV valve and the only other opening should be the opposite valve cover. If there is a big intake manifold leak, then vacuum could be getting pulled through both valve covers and into the intake(through the lifter valley), hence the oil all over everything. If the intake leak is towards the front of the engine, that would explain oil in just the front of the motor.

    Have you hooked a vacuum gauge up yet? How much vacuum is it pulling at idle?
     
  6. Handy Andy

    Handy Andy Full Access Member

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    I haven't hooked up a vacuum gauge yet. Even with the pcv valve unhooked from the carb, there is still a great deal of vacuum at the breather port on the passengers side valve cover. I didn't get a chance to check the torque on the intake bolts to see if any were loose. I did however grab a can of carb and choke cleaner and sprayed around the entire perimeter of the intake checking for leaks. No leaks from the outside. After Sunday night I have like 15 days off from my day job... probably gonna yank the intake off and have a good look at it to see if there are any cracks and inspect the gaskets to look for the leak area.

    Sorry i didn't answer it before, but I'm running Autolite 65 plugs.

    Part of me thinks the plugs fouling is a two pronged problem... I definitely think that theres a decent internal intake manifold leak happening, but I also am fairly certain that there is oil being pulled in through the PCV. I'm gonna put a couple hundred miles on it to see if the plugs foul up as bad now that I've unhooked the PCV. If they don't foul as fast then I know that's part of my problem.

    I'm almost to the point of saying screw it... I've seen quite a few LS swap setups for sale in my area on the facebook. Motor, trans, harness, ecu, and around 100k miles for roughly $1000. If I had the time, it would already be done...
     
  7. SquareRoot

    SquareRoot Full Access Member

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    I recently had a similar issue on a 350 build. The culprit? Shitty Edelbrock fiber intake gaskets. They delaminated and shifted allowing oil into the intake runners.

    The fel-pro I rings gasgets are the cats ass. Problem solved. IMG_20200213_170909484_resized.jpg
     

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