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Thread: Vacuum problem driving me NUTS!!!!!!!!

  1. #1
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    Vacuum problem driving me NUTS!!!!!!!!

    Ok 87 dodge daytona pacifica. Log t1 car about unmolested as unmolested gets outside of a replacement engine by the dealer about 5 to 6 year ago. It is a jasper engine as well. So not a junkyard non known motor. Everything is stock. So I got the car about a week ago and the stock gauge(which I know is usually off) was reading about 12 to 14. So I decided for sh*ts and grins to hook up my vacuum pump just to find out. Well stock gauge is accurate. So I do my modified vacuum harness that I do to all of these cars considering that it still had the factory harness. Didn't help. Think I gained and inch. So I was like ok came timing is off. So lined everything up and it is spot on. Moved it a tooth advanced didn't seem to help. Maybe gained a little. Catalyctic was rattling so removed that and still no gain.

    So moral of this story is
    Cam timing dead nuts on
    Vacuum lines replaced and good
    Cat out with test pipe in now
    No blowby or burning of oil. Maybe 10,000 on engine

    I'm at a loss
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  2. #2
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    And it is also acting like cam timing is off cause it doesn't kick kick until around 3500 or so.
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  3. #3
    Supporting Member II Turbo Mopar Contributor zin's Avatar
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    Re: Vacuum problem driving me NUTS!!!!!!!!

    Ignition timing is going to have the biggest effect on idle vacuum, is it "right"? Maybe try moving it around a little to see what happens there.

    Is the cal stock/correct for the car?

    I expect you tapped the actual intake to take your readings, so restrictions shouldn't be an issue...

    BTW, what does the FSM call out for "normal" vacuum? Seems like I recall having readings like this on most of my cars, so it may not be an issue... or my cars have the same problem!

    Mike
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  4. #4
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    I did screw around with ignition timing with the distributor. But not with a light just seeing if I could get vacuum higher. And I did unplug the coolant temp sensor. It did help a little but nothing drastic. I know when I drop it into drive it drop down to 8 to 10. On a hard decel I get 22. Car runs fine though. Logic module AFAIK is original. No codes btw.

    What I was curious about and I would have to confirm is what cam is in it. Isn't there a difference in degrees as far as slider vs roller? That is the only thing I could possibly come up with. And it is a 782 head on it as well so the head is correct for the cal.

    Paul
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  5. #5
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    And yes I tapped direct manifold.

    Oh and one other thing is is that I sprayed carb and choke cleaner all around intake lines, fuel injectors with no change in RPM. So no leaks AFAIK.
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  6. #6
    Supporting Member II Turbo Mopar Contributor shackwrrr's Avatar
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    Slider cam, roller followers. Mine had bad vacuum when I did that.
    Ian Adams

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  7. #7
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    Like how bad. As I am describing?
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  8. #8
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    Nope just checked with a mirror. Slider cam with flat followers.
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  9. #9
    Supporting Member II Turbo Mopar Contributor shackwrrr's Avatar
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    Re: Vacuum problem driving me NUTS!!!!!!!!

    Yeah, around 14-15 in of vacuum (different altitudes). Mine would break up at high rpms (valve float) but that could have just been crappy valve springs or something. Otherwise it ran fine.

    Have you done a leakdown/compression test?
    Brake booster hold vacuum?
    you said it was a slider cam, but were the lobes or followers worn?
    Ian Adams

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    1990 shadow
    scrapped, too rusty

    1991 Spirit R/T
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  10. #10
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    No no leak down or compression test. Lobes looked excellent. Looked brand new inside. Haven't gone as far as a leak down or compression due to it not showing obvious signs. But that was going to be my next step.

    Good question about the brake booster. Oddly I noticed a couple days ago that it had what felt like manual brakes but it went away after the first few stops. But I am not hearing any hissing but I know that doesn't mean its not. Will check that right now.
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  11. #11
    Supporting Member II Turbo Mopar Contributor GLHS60's Avatar
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    Re: Vacuum problem driving me NUTS!!!!!!!!

    My experience with running rollers on a slider cam is the cam timing was very advanced. I retarted the cam 1 tooth and it ran fine.

    Thanks
    Randy


    Quote Originally Posted by shackwrrr View Post
    Slider cam, roller followers. Mine had bad vacuum when I did that.


    Randy Hicks
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  12. #12
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Vacuum problem driving me NUTS!!!!!!!!

    Quote Originally Posted by 85boostbox View Post
    I did screw around with ignition timing with the distributor. But not with a light just seeing if I could get vacuum higher. And I did unplug the coolant temp sensor. It did help a little but nothing drastic. I know when I drop it into drive it drop down to 8 to 10. On a hard decel I get 22. Car runs fine though. Logic module AFAIK is original. No codes btw.

    What I was curious about and I would have to confirm is what cam is in it. Isn't there a difference in degrees as far as slider vs roller? That is the only thing I could possibly come up with. And it is a 782 head on it as well so the head is correct for the cal.

    Paul
    I would get an actual timing light on there before making any further changes. A stab in the dark with timing is no way to start off hunting a problem with low vac at idle IMO.

  13. #13
    The moderately moderate moderator Turbo Mopar Staff black86glhs's Avatar
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    Re: Vacuum problem driving me NUTS!!!!!!!!

    At least you don't have a rudder in your pants, that would really be drivin your nuts!!!
    Definitely compression check to make sure they aren't all low. Pinch off each vacuum line and see if the readings come up. Could be something you can't hear or missed during spraying for leaks. Could be leaking under the dash and might not be able to hear it.
    Bryan
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  14. #14
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    Ok update time. Got a light on it and timed it to 12 degrees. Distributor is not way out of wack which leads me to believe that my cam timing is on. I did gain a couple degrees. Sits at about 12 to 13 at neutral idle and about 10 in drive.

    Now if I rev and hold it a5 about 2500 it will hold 16 to 17 inches of vac and does not drop. So this definitely tells me that it is a idle only vacuum problem. This has me even more confused now.

    Paul
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    Re: Vacuum problem driving me NUTS!!!!!!!!

    Rip that slider out and install a 88 T1 or 88 TBI cam and roller's. Will be a whole diffrent car trust me. Shouldnt be that hard to track down. Just remember that you cant use 89+ cams because it will throw the cam timing out of wack. When I swapped a 88 T1 cam into my 86 NY it became a whole different car.

  16. #16
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    I will look into that
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  17. #17
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    Well did a compression test... 90 to 100 across the board and it dropped quickly??? So squirted some oil down the cylinders and shot up to 125. Still dropped quickly though.

    So sounds like rings or could it be my valve seats. Dunno.
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    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Vacuum problem driving me NUTS!!!!!!!!

    Quote Originally Posted by 85boostbox View Post
    Well did a compression test... 90 to 100 across the board and it dropped quickly??? So squirted some oil down the cylinders and shot up to 125. Still dropped quickly though.

    So sounds like rings or could it be my valve seats. Dunno.
    Yeah, that's not good at all. Have you triple checked the cam timing recently?

  19. #19
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    Yes double triple quadruple checked
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  20. #20
    The moderately moderate moderator Turbo Mopar Staff black86glhs's Avatar
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    Time for new rings. That is the issue right there.
    Bryan
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