Mark,
I believe that the breather connection on the valve cover is straight
through with no valve. The valves are in the ECV on the intake manifold (on
the 68 & 69 engines at least).
It is my guess that the lower flap valve opens upon accel. as the vacuum
increases in the manifold. It looks as though the upper valve begins to
close this same opening under extremely high vacuum. I don't know why that
would be the case, but that's what it looks like.
Peter
'68 TR250
> From: Mark Hooper <mhooper@pixelsystems.com>
> Date: Mon, 25 Feb 2002 15:41:40 -0500
> To: 'Peter Macholdt' <vze2846b@verizon.net>, 6pack list <6pack@autox.team.net>
> Subject: RE: Emission Control
>
> Great note!
>
> Question. Does this mean that there is some sort of flap valve or whatever
> hidden behind that metal cover over the outpipe in the TR6 valve cover? If
> so, how is it changed?
>
> The idle in my TR6 is a little high and rough, but drives beautifully under
> any throttle above idle. Now I am going over the system looking for carb
> leaks etc... Perhaps this valve you speak of is a source of some of the
> problems...
>
> Mark Hooper 72 TR6
>
>
> -----Original Message-----
> From: Peter Macholdt [mailto:vze2846b@verizon.net]
> Sent: Monday, February 25, 2002 12:01 PM
> To: 6pack list
> Subject: Re: Emission Control
>
>
> Thanks Larry. I'm posting this to the list because I thought it might be of
> interest to others.
>
> The answer below is a great explanation of the EVC system. It addresses my
> question about the valve in the base of the EVC unit. However, I still
> don't know what the upper spring, plunger, diaphragm and plate do. Based on
> the explanation, why is the upper part even needed? I would think that the
> lower valve would handle all the functions of the emissions system as
> described.
>
> BTW, this is an academic exercise only. I'm not going to change anything, I
> only want to understand it.
>
> Thanks,
> Peter
> '68 TR250
>
>
> From: LaJoMor@aol.com
> Date: Sun, 24 Feb 2002 23:24:17 EST
> To: vze2846b@verizon.net
> Subject: Re: Emission Control
>
>
> Peter...
> The ECV (better known as a PCV valve-positive crankcase ventilation valve)
> captures what is commonly called 'blowby'. That is the fumes from combustion
> that blows by rings or valves and ends up in the crankcase/valvecover.
>
> These emmisions are piped either to the ECV valve or directly into the air
> fillter box theoretically to be reburned through the intake manifold. This
> and the timing and carburetion settings on the car are about all the
> emission control there was on the 250. The 6s got more complicated with air
> injection and fuel vapor canisters etc. See the below paragraphs for a
> little more detailed info about PCV valves in general.
>
> Question:What is the PCV valve and what does it do? Answer:The blowby vapors
> that end up in an engine's crankcase contain moisture as well as combustion
> byproducts and unburned fuel vapors. The crankcase is sealed to prevent the
> escape of these gases into the atmosphere, but the vapors must be removed to
> prevent oil contamination that leads to sludge formation. The positive
> crankcase ventilation (PCV) system siphons these vapors from the crankcase
> and routes them into the intake manifold so they can be reburned in the
> engine. The main component in the PCV system is the PCV valve, which is
> usually located in the valve cover. A hose connects the PCV valve to the
> intake manifold. A second hose between the air cleaner and crankcase or
> other valve cover (V6 or V8 applications) provides fresh air to help flush
> the vapors out of the crankcase. Some engines have a separate air filter for
> the PCV breather hose located inside the air cleaner. The PCV valve is a
> spring-loaded valve with a specific orifice size designed to restrict the
> amount of air that's siphoned from the crankcase into the intake manifold.
> This is necessary because air drawn through the valve from the crankcase has
> a leaning effect on the fuel mixture much the same as a vacuum leak. So air
> flow through the valve must be controlled within certain limits. At idle,
> air flow is reduced because little blowby is produced. When the engine is
> cruising and vacuum is high, airflow through the PCV valve is at a maximum
> to purge the blowby vapors from the crankcase. It's important to note that
> PCV valves are sized for specific engine applications. The wrong PCV valve
> for an application can flow too much or too little air causing driveability
> problems. Varnish deposits can clog the valve, so replacement for
> preventative maintenance is recommended (every 50,000 miles usually).
>
> Hopes this answers some questions...
>
> Larry Morrison
> TR250 CD5182L
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