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

What reason would you have for doing a CO adjustment with the air filter housing off the engine anyway? I mean, other than not having the right tools to reach down into the mixture adjustment hole that is. Because not having the right tools isn't a good reason in and of itself. Nice discussion on what impact any open to air spots might have on the engine air fuel mixture, but kind of pointless, no?

I think it's part of the overall approach. It's a bit like putting the air filter on, installing the hatch covers, etc, etc, before you even start the engine. It's just not going to start if you do that. You have to sneak up on it.

Sounds like a work around approach to me. It don't take a DeLorean Guru to give the advice that you need to sort out everything else on the engine and get things working BEFORE adjusting the air fuel mixture. But we aren't exactly in a patient era, so doing things by the book kinda goes out the window. Little bits at a time though thankfully as those toll booth windows won't let you put much through all at once ;)

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Originally Posted by DMC1890

I think it's part of the overall approach. It's a bit like putting the air filter on, installing the hatch covers, etc, etc, before you even start the engine. It's just not going to start if you do that. You have to sneak up on it.

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I have to ask...
Why was the air filter off in the first place?? :deviltail:

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Originally Posted by Jonathan

Nice discussion on what impact any open to air spots might have on the engine air fuel mixture, but kind of pointless, no?

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Pointing out service manual inaccuracies is never pointless! The forum has already figured out everywhere you can stick LEDs so we might as well talk about mechanics now and then ;)

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Originally Posted by Ron

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...

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I'll have to test that on another car. Currently have a massively overbuilt PCV system, including ventilation ports on both valve covers and one on the lower crankcase. 4x air/oil separators connected to the intake and an adjustable PCV system. I take crankcase evac seriously :D

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Originally Posted by Ron

I have to ask...
Why was the air filter off in the first place?? :deviltail:

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Lots of other steps up to this point - unstuck fuel distributor piston, cleaned fuel injectors, etc. I proceeded to set the air-fuel mixture (with the air filter still removed), and observed that it made some difference if the big pipe on the oil filler was plugged or not.

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Originally Posted by FABombjoy

To add - the vacuum side should be able to breathe freely through the oil fill cap from both the side and bottom ports.

If the air/oil separator matrix were clogged that could would reduce flow to the vacuum side and cause a mixture shift. That part is sometimes called a "flame arrestor" but it spends most of it's life trying to condense oil vapors so they aren't pulled in to the intake manifold. You should able to quickly bench test the oil fill cap and verify if it can breathe or not.

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To add to this, if that oil cap gets blocked (ie excessive sludge from a blown head gasket) it will causes a situation where there is too much positive pressure in the crankcase. Which results in the PRV literally spraying engine oil out of either it's front, or rear main seals on the crank shaft. Whichever is weaker. If it's the front, the crank pulley ends up slinging it everywhere to make for a nasty mess to clean up with burning oil all over the muffler and rear bumper. If it's the rear, it'll have the bonus of prematurely ruining your clutch.