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Thread: Air-Fuel Mixture - plug up Oil Filler hose connection or not?

  1. #11
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    OK, I think I'm understanding. In this case I had tuned DC to 50% with the breather plugged, and when I unplugged it I estimate DC went up past 80%. So, in your chart, yours is more properly tuned to start with, but when you plug the breather your DC drops quite low.

    Back to an earlier question - with air cleaner and everything connected properly, isn't that still a significant source of unmetered air that you're having to tune for?
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

  2. #12
    '82 T3 Turbo FABombjoy's Avatar
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    Quote Originally Posted by DMC1890 View Post
    Back to an earlier question - with air cleaner and everything connected properly, isn't that still a significant source of unmetered air that you're having to tune for?
    There is about a 1mm (IIRC) restriction orifice at the connection to the cold start tube. Pop the vacuum line off and you can see it's pulling through a little tiny port. It's a decent amount of unmetered air but it's predictable. The flow will decrease as throttle increases. Crankcase pressure then pushes out of the larger tube and is metered.

    The vapor line has one as well. It behaves somewhat like PCV except it only flows once vacuum is present at the throttle edge tap.

    I've not tried but I suspect an actual PCV valve would be much harder to tune for, which is why they chose a fixed-orifice style PCV. The motor is already prone to oscillation and adding yet another source of air connected to a valve on a spring would probably make it quite entertaining at times.

    Megasquirt + speed density tune means I now run a genuine PCV valve with lower flow at idle and higher flow under load. The effects of the variable flow rates are accommodated for in software.
    Luke S :: 10270 :: 1982 Grey 5-Speed :: Single T3 .60/.48 Watercooled :: Borla Exhaust :: MSD Ignition :: MS3X EFI :: DevilsOwn Methanol Injection

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  3. #13
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    OK, I think I'm really understanding it now. Both vacuum ports on the CSV have the restriction, and the ports are interchangeable.

    As I said earlier, it would be good if the How To: Set CO Dwell would make it clear that the fitting should NOT be plugged (as several responders note).

    By the way, I had to start from even further back than that (I had really screwed up my AF setting due to massive vacuum leaks). I found this (http://www.cisflowtech.com/frequentl...xture-setting/), without which I could not get the engine to run at all beyond the initial starting shot.
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

  4. #14
    '82 T3 Turbo FABombjoy's Avatar
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    One way to find vacuum leaks is $20 and a spray bottle of soapy water:

    http://dmctalk.org/showthread.php?14...r-for-about-20

    Looks like DMCMW Dave chimed in on the CO howto at the end about not plugging hoses. There's no reference in the service manual about plugging it, and the data I've posted shows what can happen if you do!
    Luke S :: 10270 :: 1982 Grey 5-Speed :: Single T3 .60/.48 Watercooled :: Borla Exhaust :: MSD Ignition :: MS3X EFI :: DevilsOwn Methanol Injection

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  5. #15
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    Actually, the FSM does say in the second paragraph of D:04:01 "The engine must be run in with air filter in position. The ignition system must be serviceable and correctly set. No air leaks must be present (Brake Vacuum Hose, Ignition Advance Capsule Pipe, Fuel Lines, Oil Vapour Rebreathing Pipes etc)." But that's just one of those warnings that we tend to ignore, and perhaps in this case makes you think that you need to plug up what appears to be an air leak, when it is not.
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

  6. #16
    Admins Never Retire Ron's Avatar
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    Sorry for the confusion Robert...
    In the How To, I included removing the breather because a lot of people have complained about reaching the adjusting screw with standard tools, some had non-stock breathers, etc... Removing the breather leaves the hose from the filler cap open, which leaves the closed system open (the hose is normally under vacuum too) -- not what is expected when setting the CO dwell. Blocking it off should make it closer to (but not exactly the same as) a stock set up.... Leaving double checking it with everything hooked up as it said covering all cases.
    But it turned out to be confusing. So I edited it to make it clearer. (As said above, connected as it will run is the best.)
    Any input/suggestions/etc as to the way it is now (from anyone) would be appreciated!

  7. #17
    '82 T3 Turbo FABombjoy's Avatar
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    Well... sorta The big hose won't be under any meaningful vacuum unless the air/oil sep matrix is plugged or the engine is under heavy load. Inside the air filter housing, the breather tube gets its own dedicated section of the air filter element which is why one corner of the air filter is always oily. Here's a pic of that tube removed from the air filter housing.
    Breather Tube.jpg

    If the breather connection were simply a fitting on the side of the airbox and didn't have the little tube, it would definitely be under partial vacuum at all times. If the crankcase was always under vacuum these motors wouldn't have as many oil leaks Without significant improvement to the air/oil separator system you'll also have a very blue exhaust.

    Under heavy load, airflow to the engine increases and engine vacuum goes away (increased MAP), crankcase pressure increases and will flow from the breather tube into the intake. The low pressure airflow adjacent to the intake breather tube will encourage blowby gasses into the engine which is the only time the big hose might see lower than atmospheric pressure, assuming your rings/valve seals/etc are in good shape. If you're running a breather filter on the oil cap instead of the stock config this can exacerbate oil leaks as all blowby gasses must be pushed out into atmospheric pressure instead of the lower-than-atmospheric intake air stream. Sorry, a fluid dynamics person could probably make that sound less awkward.

    Thesis: Adjust CO with intake configuration as close to stock as possible. Do not block any vacuum/breather hoses. Blocking the big hose will slowly reduce flow through PCV vacuum hose (as demonstrated in previous data) and CO will shift lean once the intake is returned to stock form.
    Luke S :: 10270 :: 1982 Grey 5-Speed :: Single T3 .60/.48 Watercooled :: Borla Exhaust :: MSD Ignition :: MS3X EFI :: DevilsOwn Methanol Injection

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  8. #18
    Admins Never Retire Ron's Avatar
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    Quote Originally Posted by FABombjoy View Post
    ...
    If the crankcase was always under vacuum these motors wouldn't have as many oil leaks Without significant improvement to the air/oil separator system you'll also have a very blue exhaust.
    ...
    Under heavy load, airflow to the engine increases and engine vacuum goes away (increased MAP)...
    ...

    Thesis: Adjust CO with intake configuration as close to stock as possible. Do not block any vacuum/breather hoses. Blocking the big hose will slowly reduce flow through PCV vacuum hose (as demonstrated in previous data) and CO will shift lean once the intake is returned to stock form.
    hehe..this has been hashed over before.. In short;
    The manual states, "The closed crankcase system does not have an air inlet for air circulation within the crankcase.This system applies manifold vacuum to the crankcase which is completely sealed to outside air.
    ...
    An air leak in the engine crankcase will cause a lean running condition." D:06:02, 03
    (Remove the filler cap and place you palm on the bottom of it and you will believe ;-)
    Load or not there is some vacuum, but what matters here, when setting the CO, is at idle anyway...

    No argument on the "big hose..."

    (fwiw, I agree with the thesis - I've always said to set CO with everything else correct first, and, that it is best to do with everything connected, or at least double check it that way afterwards ;-)

    =======

    I can see saying there is an unmeasured "leak", as previously mentioned. But it is metered (ie known and allowed for...)

  9. #19
    '82 T3 Turbo FABombjoy's Avatar
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    I think that section of the manual is based on theory and not practice Seems you'd have to have 6 helluva perfectly sealed combustion chambers for a CC air leak to cause significant shift in mixture. The vacuum felt on the bottom of the oil fill is quickly offset by blowby gasses. Put your hand over the oil fill opening and it doesn't take long to build up! Without any notable pressure differential (as measured in real life!) between CC and atmo, air has no reason to enter the CC.

    After all these blowby gas discussions, if we meet at a DCS I'm buying you Taco Bell.
    Luke S :: 10270 :: 1982 Grey 5-Speed :: Single T3 .60/.48 Watercooled :: Borla Exhaust :: MSD Ignition :: MS3X EFI :: DevilsOwn Methanol Injection

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  10. #20
    Admins Never Retire Ron's Avatar
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    Quote Originally Posted by FABombjoy View Post
    I think that section of the manual is based on theory and not practice Seems you'd have to have 6 helluva perfectly sealed combustion chambers for a CC air leak to cause significant shift in mixture. The vacuum felt on the bottom of the oil fill is quickly offset by blowby gasses. Put your hand over the oil fill opening and it doesn't take long to build up! Without any notable pressure differential (as measured in real life!) between CC and atmo, air has no reason to enter the CC.

    After all these blowby gas discussions, if we meet at a DCS I'm buying you Taco Bell.
    Agreed, it is just there to handle what does blow by... If you haven't, actually try putting your palm on the bottom of the filler...it is very strong. If the blowby was anything close to keeping up with it, it'd be rebuild time...

    I guess it would have been clearer (in the how to) if I said something like, "there are 3 ports to consider when removing the breather, the main one for incoming air, one for it to enter the engine after filtering, and the small one going to the filler, which should be blocked off to avoid a lean condition warned about in the manual if the crankcase is not sealed." How much it matters I don't know...maybe about as much as not having to draw air through the filter and plumbing?? ...I wouldn't think it's anything like a performance engine, but when setting anything up, I like to stick to the specs.

    Tocco Bell sounds good! It'd be more likely to meet up at a Woodward Dream Cruise...that was my old stomping grounds years ago. (There or Gratiot Ave was the place to make a little change with muscle cars, until the other guys/or cops got to know your car ;-) Planning on the next one. In any case, TB makes me thirsty, 1st one is on me.

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