87 OCTANE SPARK TIMING

Discussion in 'Big Block Cadillacs' started by MIHELA, Jul 25, 2018.

  1. Darius

    Darius Well-Known Member

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  2. MIHELA

    MIHELA Active Member

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    I ripped the trans out and confirmed my suspicion.
     
  3. MIHELA

    MIHELA Active Member

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    Got my trans all put back together and in. Trucks shifts really well! The engine still shakes at idle though, and I still have persistently low MAP readings. I plan on doing a compression check, but I suspect a vacuum leak more. How common is it to have problems sealing the bottom side of the intake manifold? I cant find anything up top so far.
     
  4. kzhurley

    kzhurley Active Member

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    I had issues with my adapter plate sealing correctly when I put my holley tbi on. It ended up being I had the wrong tbi gasket leaking where the iac valve passage is in base plate.
     
  5. kzhurley

    kzhurley Active Member

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    Also I've left plugs out of the stock intake manifold that looked like plain bolt holes but were open
     
  6. MIHELA

    MIHELA Active Member

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    The TBI base gasket is correct, my TBI and adapter came off the same truck. I am going to check the adapter to the manifold again though.
     
  7. Darius

    Darius Well-Known Member

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    Just to add another voice, my first thought was a vacuum leak. Hope it’s an easy one to identify.

    Best,

    Bro. d
     
  8. kzhurley

    kzhurley Active Member

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    Do you have stock intake?
     
  9. kzhurley

    kzhurley Active Member

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    Do you have stock intake? If so I bet that's a where the issue is. Cad intakes have a very thin gasket dealing surface that follows the throttle bores pretty closely. The 454 tbi adapter is more oval shaped and doesn't dip in between the primary and secondaries.
    Found this out the hard way lol.
     
  10. MIHELA

    MIHELA Active Member

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    I found out as well. I ended up with an earlier quadrajet style 454 gasket, and some rtv at front and back. The 454 TBI adapter is similarly minimalist and doesn't match there.
     
  11. MIHELA

    MIHELA Active Member

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  12. MIHELA

    MIHELA Active Member

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    Got my new gaskets, same problem. Ran a compression check, 0 PSI on cylinder 2. All the others were in the 150-170 range. Well that explains the shake! I suppose I must have a problem valve.
     
  13. Darius

    Darius Well-Known Member

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    EEK! Sorry.

    bro. d
     
  14. MIHELA

    MIHELA Active Member

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    I pulled the LH valve cover and discovered the exhaust valve was open and the rocker cocked to the side. When I was assembling the engine I must have bumped the pushrod out of the lifter and it had jammed on the edge of the lifter bore, just enough to contain the lifter. I put everything back in place and cranked the motor and had 165 in that cylinder. Everything moves as it should but the darkness and the mosquitoes came before I could button everything up, so I'll fire it back up tomorrow and see how it goes.
     
  15. Darius

    Darius Well-Known Member

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    So, nothing was gouged or bent??

    d
     
  16. MIHELA

    MIHELA Active Member

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    There was a little ding on the edge of the pushrod ball and on the side of the pushrod, both minor. It was just enough to hang the valve but not enough to bend anything.
     
  17. MIHELA

    MIHELA Active Member

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    Buttoned everything up and went for a drive, MAP values look normal, idles at about 35-40 kPa, set min air and got 20 IAC counts dialed in, shake is gone. Runs like it was meant to. I had to turn the fuel back to where I started to get it to run, I can't believe it worked before at all!
     
    El Diablo and kzhurley like this.
  18. MIHELA

    MIHELA Active Member

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    [​IMG]

    Here's my latest VE table. It's been running very well.
     
  19. MIHELA

    MIHELA Active Member

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    [​IMG]
    And here's my SA table. Kind of what I started this thread for.
     
  20. kzhurley

    kzhurley Active Member

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    Your spark table is very close to what I've come up with in tunerstudio for my megasquirt. I'm still tuning cruise yet though.
    I tried to copy the factory curve as a starting point. The I just tweaked it where I thought it would like it. Like my motor cranks with only 8° initial but once it starts it idles about 16° or so.
    Also just below my idle rpm I advanced it 2 or 3° so if it drops into those cells the timing would bring the idle back up to where it's supposed to be. Much quicker reaction than trying to do it with iac. Works well when put in gear or when the electric fan kicks in
     
    Last edited: Aug 11, 2018

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